diff options
| author | Ulrich Drepper <drepper@redhat.com> | 1998-07-13 12:29:13 +0000 |
|---|---|---|
| committer | Ulrich Drepper <drepper@redhat.com> | 1998-07-13 12:29:13 +0000 |
| commit | 7a68c94a5b8fb848590857f7d8c4a271bf4e8ea9 (patch) | |
| tree | f91b98eed7220f1cb3b29337ca432d323c7b7408 /manual/math.texi | |
| parent | ceb27555a1f637c048c7ec65a01f8122c3e79bf3 (diff) | |
| download | glibc-7a68c94a5b8fb848590857f7d8c4a271bf4e8ea9.tar glibc-7a68c94a5b8fb848590857f7d8c4a271bf4e8ea9.tar.gz glibc-7a68c94a5b8fb848590857f7d8c4a271bf4e8ea9.tar.bz2 glibc-7a68c94a5b8fb848590857f7d8c4a271bf4e8ea9.zip | |
Update.
1998-07-10 18:14 -0400 Zack Weinberg <zack@rabi.phys.columbia.edu>
* manual/Makefile: Overhauled. Generate libc.texinfo from the
chapter files. Exorcise the chapters, chapters-incl mess.
Support inserting doc chapters from add-on modules.
(chapters): New variable.
(add-chapters): New variable.
(appendices): New variable.
(libc.texinfo): New target.
(clean): Fix bugs.
(realclean): Fix bugs.
* manual/texis.awk: New file.
* manual/libc-texinfo.sh: New file.
* manual/libc-texinfo.in: New file.
* manual/conf.texi (top @node): Remove next pointer.
* manual/lang.texi (top @node): Remove prev pointer.
* manual/job.texi (top @node): Add explicit pointers.
* manual/message.texi (top @node): Add explicit pointers.
* manual/nss.texi (top @node): Add explicit pointers.
* manual/process.texi (top @node): Add explicit pointers.
* manual/startup.texi (top @node): Add explicit pointers.
* manual/terminal.texi (top @node): Add explicit pointers.
* manual/users.texi (top @node): Add explicit pointers.
* manual/arith.texi: Add %MENU% tag.
* manual/conf.texi: Add %MENU% tag.
* manual/contrib.texi: Add %MENU% tag.
* manual/ctype.texi: Add %MENU% tag.
* manual/errno.texi: Add %MENU% tag.
* manual/filesys.texi: Add %MENU% tag.
* manual/header.texi: Add %MENU% tag.
* manual/install.texi: Add %MENU% tag.
* manual/intro.texi: Add %MENU% tag.
* manual/io.texi: Add %MENU% tag.
* manual/job.texi: Add %MENU% tag.
* manual/lang.texi: Add %MENU% tag.
* manual/llio.texi: Add %MENU% tag.
* manual/locale.texi: Add %MENU% tag.
* manual/maint.texi: Add %MENU% tag.
* manual/math.texi: Add %MENU% tag.
* manual/mbyte.texi: Add %MENU% tag.
* manual/memory.texi: Add %MENU% tag.
* manual/message.texi: Add %MENU% tag.
* manual/nss.texi: Add %MENU% tag.
* manual/pattern.texi: Add %MENU% tag.
* manual/pipe.texi: Add %MENU% tag.
* manual/process.texi: Add %MENU% tag.
* manual/search.texi: Add %MENU% tag.
* manual/setjmp.texi: Add %MENU% tag.
* manual/signal.texi: Add %MENU% tag.
* manual/socket.texi: Add %MENU% tag.
* manual/startup.texi: Add %MENU% tag.
* manual/stdio.texi: Add %MENU% tag.
* manual/string.texi: Add %MENU% tag.
* manual/sysinfo.texi: Add %MENU% tag.
* manual/terminal.texi: Add %MENU% tag.
* manual/time.texi: Add %MENU% tag.
* manual/users.texi: Add %MENU% tag.
1998-07-13 Ulrich Drepper <drepper@cygnus.com>
* sysdeps/unix/sysv/linux/i386/dl-procinfo.h (x86_cap_flags):
Update.
1998-07-11 Andreas Jaeger <aj@arthur.rhein-neckar.de>
* sysdeps/unix/sysv/linux/recvmsg.c (__libc_recvmsg): Use ANSI
style declaration to avoid warning.
* sysdeps/unix/sysv/linux/sendmsg.c (__libc_sendmsg): Likewise.
1998-07-04 Mark Kettenis <kettenis@phys.uva.nl>
* elf/rtld.c (process_dl_debug): Add missing continue.
1998-07-12 Mark Kettenis <kettenis@phys.uva.nl>
* elf/rtld.c (_dl_skip_args): Make global because the Hurd startup
code needs it.
1998-07-10 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de>
* Makeconfig ($(common-objpfx)sysd-dirs): Write out definition of
sysd-dirs-done.
* Makerules: Don't generate version maps too early.
($(common-objpfx)sysd-versions): Force regeneration if the list of
subdirs has changed.
1998-07-10 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de>
* elf/dlfcn.h (DL_CALL_FCT): Use portable comma expression.
1998-07-11 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de>
* iconv/gconv_db.c (gen_steps): Always set *handle and *nsteps.
* iconv/gconv_dl.c (__gconv_find_shlib): Correct use of tfind
return value.
1998-07-12 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de>
* elf/dl-open.c (dl_open_worker): New function.
(_dl_open): Call it to do the actual work while catching errors.
* elf/dl-close.c (_dl_close): Only call termination function if
the initialisation function was called.
1998-07-13 Ulrich Drepper <drepper@cygnus.com>
* libio/libioP.h (_IO_cleanup_registration_needed): Use __PMT.
Reported by Felix von Leitner <leitner@amdiv.de>.
1998-07-13 10:28 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de>
* elf/rtld.c (process_dl_debug): Add missing continue.
1998-06-23 Mark Kettenis <kettenis@phys.uva.nl>
Diffstat (limited to 'manual/math.texi')
| -rw-r--r-- | manual/math.texi | 1395 |
1 files changed, 454 insertions, 941 deletions
diff --git a/manual/math.texi b/manual/math.texi index 1991bfbdb8..10b326287e 100644 --- a/manual/math.texi +++ b/manual/math.texi @@ -1,739 +1,129 @@ @c We need some definitions here. +@ifclear mult @ifhtml -@set mult · +@set mult · +@set infty ∞ +@set pie π @end ifhtml @iftex @set mult @cdot +@set infty @infty @end iftex @ifclear mult -@set mult x +@set mult * +@set infty oo +@set pie pi @end ifclear @macro mul @value{mult} @end macro -@iftex -@set infty @infty -@end iftex -@ifclear infty -@set infty oo -@end ifclear @macro infinity @value{infty} @end macro +@ifnottex +@macro pi +@value{pie} +@end macro +@end ifnottex +@end ifclear @node Mathematics, Arithmetic, Low-Level Terminal Interface, Top +@c %MENU% Math functions, useful constants, random numbers @chapter Mathematics This chapter contains information about functions for performing mathematical computations, such as trigonometric functions. Most of these functions have prototypes declared in the header file -@file{math.h}. +@file{math.h}. The complex-valued functions are defined in +@file{complex.h}. @pindex math.h - -For all functions which take a single floating-point argument and for -several other functions as well there are three different functions -available for the type @code{double}, @code{float}, and @code{long -double}. The @code{double} versions of the functions are mostly defined -even in the @w{ISO C 89} standard. The @code{float} and @code{long -double} variants are introduced in the numeric extensions for the C -language which are part of the @w{ISO C 9X} standard. - -Which of the three versions of the function should be used depends on -the situation. For most functions and implementation it is true that -speed and precision do not go together. I.e., the @code{float} versions -are normally faster than the @code{double} and @code{long double} -versions. On the other hand the @code{long double} version has the -highest precision. One should always think about the actual needs and -in case of double using @code{double} is a good compromise. - +@pindex complex.h + +All mathematical functions which take a floating-point argument +have three variants, one each for @code{double}, @code{float}, and +@code{long double} arguments. The @code{double} versions are mostly +defined in @w{ISO C 89}. The @code{float} and @code{long double} +versions are from the numeric extensions to C included in @w{ISO C 9X}. + +Which of the three versions of a function should be used depends on the +situation. For most calculations, the @code{float} functions are the +fastest. On the other hand, the @code{long double} functions have the +highest precision. @code{double} is somewhere in between. It is +usually wise to pick the narrowest type that can accomodate your data. +Not all machines have a distinct @code{long double} type; it may be the +same as @code{double}. @menu -* Domain and Range Errors:: Detecting overflow conditions and the like. -* Exceptions in Math Functions:: Signalling exception in math functions. -* Mathematical Constants:: Precise numeric values for often used - constant. -* FP Comparison Functions:: Special functions to compare floating-point - numbers. -* FP Function Optimizations:: Fast code or small code. -* Trig Functions:: Sine, cosine, and tangent. -* Inverse Trig Functions:: Arc sine, arc cosine, and arc tangent. -* Exponents and Logarithms:: Also includes square root. -* Hyperbolic Functions:: Hyperbolic sine and friends. -* Pseudo-Random Numbers:: Functions for generating pseudo-random - numbers. +* Mathematical Constants:: Precise numeric values for often-used + constants. +* Trig Functions:: Sine, cosine, tangent, and friends. +* Inverse Trig Functions:: Arcsine, arccosine, etc. +* Exponents and Logarithms:: Also pow and sqrt. +* Hyperbolic Functions:: sinh, cosh, tanh, etc. +* Special Functions:: Bessel, gamma, erf. +* Pseudo-Random Numbers:: Functions for generating pseudo-random + numbers. +* FP Function Optimizations:: Fast code or small code. @end menu -@node Domain and Range Errors -@section Domain and Range Errors - -@cindex domain error -Many of the functions listed in this chapter are defined mathematically -over a domain that is only a subset of real numbers. For example, the -@code{acos} function is defined over the domain between @code{@minus{}1} and -@code{1}. If you pass an argument to one of these functions that is -outside the domain over which it is defined, the function sets -@code{errno} to @code{EDOM} to indicate a @dfn{domain error}. On -machines that support @w{IEEE 754} floating point, functions reporting -error @code{EDOM} also return a NaN. - -Some of these functions are defined mathematically to result in a -complex value over parts of their domains. The most familiar example of -this is taking the square root of a negative number. The functions in -this chapter take only real arguments and return only real values; -therefore, if the value ought to be nonreal, this is treated as a domain -error. - -@cindex range error -A related problem is that the mathematical result of a function may not -be representable as a floating point number. If magnitude of the -correct result is too large to be represented, the function sets -@code{errno} to @code{ERANGE} to indicate a @dfn{range error}, and -returns a particular very large value (named by the macro -@code{HUGE_VAL}) or its negation (@code{@minus{}HUGE_VAL}). - -If the magnitude of the result is too small, a value of zero is returned -instead. In this case, @code{errno} might or might not be -set to @code{ERANGE}. - -The only completely reliable way to check for domain and range errors is -to set @code{errno} to @code{0} before you call the mathematical function -and test @code{errno} afterward. As a consequence of this use of -@code{errno}, use of the mathematical functions is not reentrant if you -check for errors. - -@c ### This is no longer true. --drepper -@c None of the mathematical functions ever generates signals as a result of -@c domain or range errors. In particular, this means that you won't see -@c @code{SIGFPE} signals generated within these functions. (@xref{Signal -@c Handling}, for more information about signals.) - -@comment math.h -@comment ISO -@deftypevr Macro double HUGE_VAL -An expression representing a particular very large number. On machines -that use @w{IEEE 754}/@w{IEEE 854} floating point format, the value is -``infinity''. On other machines, it's typically the largest positive -number that can be represented. - -The value of this macro is used as the return value from various -mathematical @code{double} returning functions in overflow situations. -@end deftypevr - -@comment math.h -@comment ISO -@deftypevr Macro float HUGE_VALF -This macro is similar to the @code{HUGE_VAL} macro except that it is -used by functions returning @code{float} values. - -This macro is introduced in @w{ISO C 9X}. -@end deftypevr - -@comment math.h -@comment ISO -@deftypevr Macro {long double} HUGE_VALL -This macro is similar to the @code{HUGE_VAL} macro except that it is -used by functions returning @code{long double} values. The value is -only different from @code{HUGE_VAL} if the architecture really supports -@code{long double} values. - -This macro is introduced in @w{ISO C 9X}. -@end deftypevr - - -A special case is the @code{ilogb} function @pxref{Exponents and -Logarithms}. Since the return value is an integer value, one cannot -compare with @code{HUGE_VAL} etc. Therefore two further values are -defined. - -@comment math.h -@comment ISO -@deftypevr Macro int FP_ILOGB0 -This value is returned by @code{ilogb} if the argument is @code{0}. The -numeric value is either @code{INT_MIN} or @code{-INT_MAX}. - -This macro is introduced in @w{ISO C 9X}. -@end deftypevr - -@comment math.h -@comment ISO -@deftypevr Macro int FP_ILOGBNAN -This value is returned by @code{ilogb} if the argument is @code{NaN}. The -numeric value is either @code{INT_MIN} or @code{INT_MAX}. - -This macro is introduced in @w{ISO C 9X}. -@end deftypevr - - -For more information about floating-point representations and limits, -see @ref{Floating Point Parameters}. In particular, the macro -@code{DBL_MAX} might be more appropriate than @code{HUGE_VAL} for many -uses other than testing for an error in a mathematical function. - - -@node Exceptions in Math Functions -@section Exceptions in Math Functions -@cindex exception -@cindex signal - -Due to the restrictions in the size of the floating-point number -representation or the limitation of the input range of certain functions -some of the mathematical operations and functions have to signal -exceptional situations. The @w{IEEE 754} standard specifies which -exceptions have to be supported and how they can be handled. - -@w{IEEE 754} specifies two actions for floating-point exception: taking -a trap or continuing without doing so. If the trap is taken a -(possibly) user defined trap handler is called and this function can -correct the argument or react somehow else on the call. If the trap -handler returns, its return value is taken as the result of the -operation. - -If no trap handler is called each of the known exceptions has a default -action. This consists of setting a corresponding bit in the -floating-point status word to indicate which kind of exception was -raised and to return a default value, which depends on the exception -(see the table below). - -@noindent -The exceptions defined in @w{IEEE 754} are: - -@table @samp -@item Invalid Operation -This exception is raised if the given operands are invalid for the -operation to be performed. Examples are -(see @w{IEEE 754}, @w{section 7}): -@enumerate -@item -Any operation on a signalling NaN. -@item -Addition or subtraction; magnitude subtraction of infinities such as -@math{(+@infinity{}) + (-@infinity{})}. -@item -Multiplication: -@math{0 @mul{} @infinity{}}. - -@item -Division: @math{0/0} or @math{@infinity{}/@infinity{}}. - -@item -Remainder: @math{x} REM @math{y}, where @math{y} is zero or @math{x} is -infinite. -@item -Square root if the operand is less then zero. -@item -Conversion of an internal floating-point number to an integer or to a -decimal string when overflow, infinity, or NaN precludes a faithful -representation in that format and this cannot otherwise be signaled. -@item -Conversion of an unrecognizable input string. -@item -Comparison via predicates involving @math{<} or @math{>}, without -@code{?}, when the operands are @dfn{unordered}. (@math{?>} means the -unordered greater relation, @xref{FP Comparison Functions}). -@end enumerate - -If the exception does not cause a trap handler to be called the result -of the operation is taken as a quiet NaN. - -@item Division by Zero -This exception is raised if the divisor is zero and the dividend is a -finite nonzero number. If no trap occurs the result is either -@math{+@infinity{}} or @math{-@infinity{}}, depending on the -signs of the operands. - -@item Overflow -This exception is signalled whenever the result cannot be represented -as a finite value in the precision format of the destination. If no trap -occurs the result depends on the sign of the intermediate result and the -current rounding mode (@w{IEEE 754}, @w{section 7.3}): -@enumerate -@item -Round to nearest carries all overflows to @math{@infinity{}} -with the sign of the intermediate result. -@item -Round toward @math{0} carries all overflows to the precision's largest -finite number with the sign of the intermediate result. -@item -Round toward @math{-@infinity{}} carries positive overflows to the -precision's largest finite number and carries negative overflows to -@math{-@infinity{}}. - -@item -Round toward @math{@infinity{}} carries negative overflows to the -precision's most negative finite number and carries positive overflows -to @math{@infinity{}}. -@end enumerate - -@item Underflow -The underflow exception is created when an intermediate result is too -small for the operation or if the operations result rounded to the -destination precision causes a loss of accuracy by approximating the -result by denormalized numbers. - -When no trap is installed for the underflow exception, underflow shall -be signaled (via the underflow flag) only when both tininess and loss of -accuracy have been detected. If no trap handler is installed the -operation continues with an inprecise small value or zero if the -destination precision cannot hold the small exact result. - -@item Inexact -This exception is signalled if the rounded result is not exact (such as -computing the square root of two) or the result overflows without an -overflow trap. -@end table - -To control whether an exception causes a trap to occur all @w{IEEE 754} -conformant floating-point implementations (either hardware or software) -have a control word. By setting specific bits for each exception in -this control word the programmer can decide whether a trap is wanted or -not. - -@w{ISO C 9X} introduces a set of function which can be used to control -exceptions. There are functions to manipulate the control word, to -query the status word or to save and restore the whole state of the -floating-point unit. There are also functions to control the rounding -mode used. - -@menu -* Status bit operations:: Manipulate the FP status word. -* FPU environment:: Controlling the status of the FPU. -* Rounding Modes:: Controlling the rounding mode. -@end menu - -@node Status bit operations -@subsection Controlling the FPU status word - -To control the five types of exceptions defined in @w{IEEE 754} some -functions are defined which abstract the interface to the FPU. The -actual implementation can be very different, depending on the underlying -hardware or software. - -To address the single exception the @file{fenv.h} headers defines a -number of macros: - -@vtable @code -@comment fenv.h -@comment ISO -@item FE_INEXACT -Represents the inexact exception iff the FPU supports this exception. -@comment fenv.h -@comment ISO -@item FE_DIVBYZERO -Represents the divide by zero exception iff the FPU supports this exception. -@comment fenv.h -@comment ISO -@item FE_UNDERFLOW -Represents the underflow exception iff the FPU supports this exception. -@comment fenv.h -@comment ISO -@item FE_OVERFLOW -Represents the overflow exception iff the FPU supports this exception. -@comment fenv.h -@comment ISO -@item FE_INVALID -Represents the invalid exception iff the FPU supports this exception. -@end vtable - -The macro @code{FE_ALL_EXCEPT} is the bitwise OR of all exception macros -which are supported by the FP implementation. - -Each of the supported exception flags can either be set or unset. The -@w{ISO C 9X} standard defines functions to set, unset and test the -status of the flags. - -@comment fenv.h -@comment ISO -@deftypefun void feclearexcept (int @var{excepts}) -This function clears all of the supported exception flags denoted by -@var{excepts} in the status word. -@end deftypefun - -To safe the current status of the flags in the status word @file{fenv.h} -defines the type @code{fexcept_t} which can hold all the information. -The following function can be used to retrieve the current setting. - -@comment fenv.h -@comment ISO -@deftypefun void fegetexceptflag (fexcept_t *@var{flagp}, int @var{excepts}) -Store in the variable pointed to by @var{flagp} an -implementation-defined value representing the current setting of the -exception flags indicated by the parameter @var{excepts}. -@end deftypefun - -@noindent -To restore the previously saved values one can use this function: - -@comment fenv.h -@comment ISO -@deftypefun void fesetexceptflag (const fexcept_t *@var{flagp}, int @var{excepts}) -Restore from the variable pointed to by @var{flagp} the setting of the -flags for the exceptions denoted by the value of the parameter -@var{excepts}. -@end deftypefun - -The last function allows to query the current status of the flags. The -flags can be set either explicitely (using @code{fesetexceptflag} or -@code{feclearexcept}) or by a floating-point operation which happened -before. Since the flags are accumulative, the flags must be explicitely -reset using @code{feclearexcept} if one wants to test for a certain -exceptions raised by a specific piece of code. - -@comment fenv.h -@comment ISO -@deftypefun int fetestexcept (int @var{excepts}) -Test whether a subset of the flags indicated by the parameter -@var{except} is currently set. If yes, a nonzero value is returned -which specifies which exceptions are set. Otherwise the result is zero. -@end deftypefun - -@noindent -Code which uses the @code{fetestexcept} function could look like this: - -@smallexample -@{ - double f; - int raised; - feclearexcept (FE_ALL_EXCEPT); - f = compute (); - raised = fetestexcept (FE_OVERFLOW | FE_INVALID); - if (raised & FE_OVERFLOW) @{ /* ... */ @} - if (raised & FE_INVALID) @{ /* ... */ @} - /* ... */ -@} -@end smallexample - -Please note that the return value of @code{fetestexcept} is @code{int} -but this does not mean that the @code{fexcept_t} type is generally -representable as an integer. These are completely independent types. - - -@node FPU environment -@subsection Controlling the Floating-Point environment - -It is sometimes necessary so save the complete status of the -floating-point unit for a certain time to perform some completely -different actions. Beside the status of the exception flags, the -control word for the exceptions and the rounding mode can be saved. - -The file @file{fenv.h} defines the type @code{fenv_t}. The layout of a -variable of this type is implementation defined but the variable is able -to contain the complete status information. To fill a variable of this -type one can use this function: - -@comment fenv.h -@comment ISO -@deftypefun void fegetenv (fenv_t *@var{envp}) -Store the current floating-point environment in the object pointed to by -@var{envp}. -@end deftypefun - -@noindent -Another possibility which is useful in several situations is - -@comment fenv.h -@comment ISO -@deftypefun int feholdexcept (fenv_t *@var{envp}) -Store the current floating-point environment in the object pointed to by -@var{envp}. Afterwards, all exception flags are cleared and if -available a mode is installed which continues on all exceptions and does -not cause a trap to occur. In this case a nonzero value is returned. - -If the floating-point implementation does not support such a non-stop -mode, the return value is zero. -@end deftypefun - -The functions which allow a state of the floating-point unit to be -restored can take two kinds of arguments: - -@itemize @bullet -@item -Pointers to @code{fenv_t} objects which were initialized previously by a -call to @code{fegetenv} or @code{feholdexcept}. -@item -@vindex FE_DFL_ENV -The special macro @code{FE_DFL_ENV} which represents the floating-point -environment as it was available at program start. -@item -Implementation defined macros with names starting with @code{FE_}. - -@vindex FE_NOMASK_ENV -If possible, the GNU C Library defines a macro @code{FE_NOMASK_ENV} -which represents an environment where no exceptions are masked, so every -exception raised causes a trap to occur. You can test for this macro -using @code{#ifdef}. - -Some platforms might define other predefined environments. -@end itemize - -@noindent -To set any of the environments there are two functions defined. - -@deftypefun void fesetenv (const fenv_t *@var{envp}) -Establish the floating-point environment described in the object pointed -to by @var{envp}. Even if one or more exceptions flags in the restored -environment are set no exception is raised. -@end deftypefun - -In some situations the previous status of the exception flags must not -simply be discarded and so this function is useful: - -@deftypefun void feupdateenv (const fenv_t *@var{envp}) -The current status of the floating-point unit is preserved in some -automatic storage before the environment described by the object pointed -to by @var{envp} is installed. Once this is finished all exceptions set -in the original environment which is saved in the automatic storage, is -raised. -@end deftypefun - -This function can be used to execute a part of the program with an -environment which masks all exceptions and before switching back remove -unwanted exception and raise the remaining exceptions. - - -@node Rounding Modes -@subsection Rounding modes of the Floating-Point Unit - -@w{IEEE 754} defines four different rounding modes. If the rounding -mode is supported by the floating-point implementation the corresponding -of the following macros is defined: - -@table @code -@comment fenv.h -@comment ISO -@vindex FE_TONEAREST -@item FE_TONEAREST -Round to nearest. This is the default mode and should always be used -except when a different mode is explicitely required. Only rounding to -nearest guarantees numeric stability of the computations. - -@comment fenv.h -@comment ISO -@vindex FE_UPWARD -@item FE_UPWARD -Round toward @math{+@infinity{}}. - -@comment fenv.h -@comment ISO -@vindex FE_DOWNWARD -@item FE_DOWNWARD -Round toward @math{-@infinity{}}. - -@comment fenv.h -@comment ISO -@vindex FE_TOWARDZERO -@item FE_TOWARDZERO -Round toward zero. -@end table - -At any time one of the above four rounding modes is selected. To get -information about the currently selected mode one can use this function: - -@comment fenv.h -@comment ISO -@deftypefun int fegetround (void) -Return the currently selected rounding mode, represented by one of the -values of the defined rounding mode macros. -@end deftypefun - -@noindent -To set a specific rounding mode the next function can be used. - -@comment fenv.h -@comment ISO -@deftypefun int fesetround (int @var{round}) -Change the currently selected rounding mode to the mode described by the -parameter @var{round}. If @var{round} does not correspond to one of the -supported rounding modes nothing is changed. - -The function returns a nonzero value iff the requested rounding mode can -be established. Otherwise zero is returned. -@end deftypefun - -Changing the rounding mode might be necessary for various reasons. But -changing the mode only to round a given number normally is no good idea. -The standard defines a set of functions which can be used to round an -argument according to some rules and for all of the rounding modes there -is a corresponding function. - -If a large set of number has to be rounded it might be good to change -the rounding mode and to not use the function the library provides. So -the perhaps necessary switching of the rounding mode in the library -function can be avoided. But since not all rounding modes are -guaranteed to exist on any platform this possible implementation cannot -be portably used. A default method has to be implemented as well. - - @node Mathematical Constants @section Predefined Mathematical Constants @cindex constants @cindex mathematical constants -The header @file{math.h} defines a series of mathematical constants if -@code{_BSD_SOURCE} or a more general feature select macro is defined -before including this file. All values are defined as preprocessor -macros starting with @code{M_}. The collection includes: +The header @file{math.h} defines several useful mathematical constants. +All values are defined as preprocessor macros starting with @code{M_}. +The values provided are: @vtable @code @item M_E -The value is that of the base of the natural logarithm. +The base of natural logarithms. @item M_LOG2E -The value is computed as the logarithm to base @code{2} of @code{M_E}. +The logarithm to base @code{2} of @code{M_E}. @item M_LOG10E -The value is computed as the logarithm to base @code{10} of @code{M_E}. +The logarithm to base @code{10} of @code{M_E}. @item M_LN2 -The value is computed as the natural logarithm of @code{2}. +The natural logarithm of @code{2}. @item M_LN10 -The value is computed as the natural logarithm of @code{10}. +The natural logarithm of @code{10}. @item M_PI -The value is those of the number pi. +Pi, the ratio of a circle's circumrefence to its diameter. @item M_PI_2 -The value is those of the number pi divided by two. +Pi divided by two. @item M_PI_4 -The value is those of the number pi divided by four. +Pi divided by four. @item M_1_PI -The value is the reziprocal of the value of the number pi. +The reciprocal of pi (1/pi) @item M_2_PI -The value is two times the reziprocal of the value of the number pi. +Two times the reciprocal of pi. @item M_2_SQRTPI -The value is two times the reziprocal of the square root of the number pi. +Two times the reciprocal of the square root of pi. @item M_SQRT2 -The value is the square root of the value of the number pi. +The square root of two. @item M_SQRT1_2 -The value is the reziprocal of the square root of the value of the number pi. +The reciprocal of the square root of two (also the square root of 1/2). @end vtable -All values are defined as @code{long double} values unless the compiler -does not support this type or @code{__STDC__} is not defined (both is -unlikely). Historically the numbers were @code{double} values and some -old code still relies on this so you might want to add explicit casts if -the extra precision of the @code{long double} value is not needed. One -critical case are functions with a variable number of arguments, such as -@code{printf}. +These constants come from the Unix98 standard and were also available in +4.4BSD; therefore, they are only defined if @code{_BSD_SOURCE} or +@code{_XOPEN_SOURCE=500}, or a more general feature select macro, is +defined. The default set of features includes these constants. +@xref{Feature Test Macros}. + +All values are of type @code{double}. As an extension, the GNU C +library also defines these constants with type @code{long double}. The +@code{long double} macros have a lowercase @samp{l} appended to their +names: @code{M_El}, @code{M_PIl}, and so forth. These are only +available if @code{_GNU_SOURCE} is defined. @vindex PI @emph{Note:} Some programs use a constant named @code{PI} which has the -same value as @code{M_PI}. This probably derives from Stroustroup's -book about his C++ programming language where this value is used in -examples (and perhaps some AT&T headers contain this value). But due to -possible name space problems (@code{PI} is a quite frequently used name) -this value is not added to @file{math.h}. Every program should use -@code{M_PI} instead or add on the compiler command line -@code{-DPI=M_PI}. - - -@node FP Comparison Functions -@section Floating-Point Comparison Functions -@cindex unordered comparison - -The @w{IEEE 754} standards defines a set of functions which allows to -compare even those numbers which normally would cause an exception to be -raised since they are unordered. E.g., the expression - -@smallexample -int v = a < 1.0; -@end smallexample - -@noindent -would raise an exception if @var{a} would be a NaN. Functions to -compare unordered numbers are part of the FORTRAN language for a long -time and the extensions in @w{ISO C 9X} finally introduce them as well -for the C programming language. - -All of the operations are implemented as macros which allow their -arguments to be of either @code{float}, @code{double}, or @code{long -double} type. - -@comment math.h -@comment ISO -@deftypefn {Macro} int isgreater (@emph{real-floating} @var{x}, @emph{real-floating} @var{y}) -This macro determines whether the argument @var{x} is greater than -@var{y}. This is equivalent to @code{(@var{x}) > (@var{y})} but no -exception is raised if @var{x} or @var{y} are unordered. -@end deftypefn - -@comment math.h -@comment ISO -@deftypefn {Macro} int isgreaterequal (@emph{real-floating} @var{x}, @emph{real-floating} @var{y}) -This macro determines whether the argument @var{x} is greater than or -equal to @var{y}. This is equivalent to @code{(@var{x}) >= (@var{y})} but no -exception is raised if @var{x} or @var{y} are unordered. -@end deftypefn - -@comment math.h -@comment ISO -@deftypefn {Macro} int isless (@emph{real-floating} @var{x}, @emph{real-floating} @var{y}) -This macro determines whether the argument @var{x} is less than @var{y}. -This is equivalent @code{(@var{x}) < (@var{y})} but no exception is raised if -@var{x} or @var{y} are unordered. -@end deftypefn - -@comment math.h -@comment ISO -@deftypefn {Macro} int islessequal (@emph{real-floating} @var{x}, @emph{real-floating} @var{y}) -This macro determines whether the argument @var{x} is less than or equal -to @var{y}. This is equivalent to @code{(@var{x}) <= (@var{y})} but no -exception is raised if @var{x} or @var{y} are unordered. -@end deftypefn - -@comment math.h -@comment ISO -@deftypefn {Macro} int islessgreater (@emph{real-floating} @var{x}, @emph{real-floating} @var{y}) -This macro determines whether the argument @var{x} is less or greater -than @var{y}. This is equivalent to @code{(@var{x}) < (@var{y}) || -(@var{x}) > (@var{y})} (except that @var{x} and @var{y} are only -evaluated once) but no exception is raised if @var{x} or @var{y} are -unordered. -@end deftypefn - -@comment math.h -@comment ISO -@deftypefn {Macro} int isunordered (@emph{real-floating} @var{x}, @emph{real-floating} @var{y}) -This macro determines whether its arguments are unordered. -@end deftypefn - -All the macros are defined in a way to ensure that both arguments are -evaluated exactly once and so they can be used exactly like the builtin -operators. - -On several platform these macros are mapped to efficient instructions -the processor understands. But on machines missing these functions, the -macros above might be rather slow. So it is best to use the builtin -operators unless it is necessary to use unordered comparisons. - -@strong{Note:} There are no macros @code{isequal} or @code{isunequal}. -These macros are not necessary since the @w{IEEE 754} standard requires -that the comparison for equality and unequality do @emph{not} throw an -exception if one of the arguments is an unordered value. - - -@node FP Function Optimizations -@section Is Fast Code or Small Code preferred? -@cindex Optimization - -If an application uses many floating point function it is often the case -that the costs for the function calls itselfs are not neglectable. -Modern processor implementation often can execute the operation itself -very fast but the call means a disturbance of the control flow. - -For this reason the GNU C Library provides optimizations for many of the -frequently used math functions. When the GNU CC is used and the user -activates the optimizer several new inline functions and macros get -defined. These new functions and macros have the same names as the -library function and so get used instead of the later. In case of -inline functions the compiler will decide whether it is reasonable to -use the inline function and this decision is usually correct. - -For the generated code this means that no calls to the library functions -are necessary. This increases the speed significantly. But the -drawback is that the code size increases and this increase is not always -neglectable. - -In cases where the inline functions and macros are not wanted the symbol -@code{__NO_MATH_INLINES} should be defined before any system header is -included. This will make sure only library functions are used. Of -course it can be determined for each single file in the project whether -giving this option is preferred or not. - +same value as @code{M_PI}. This constant is not standard; it may have +appeared in some old AT&T headers, and is mentioned in Stroustrup's book +on C++. It infringes on the user's name space, so the GNU C library +does not define it. Fixing programs written to expect it is simple: +replace @code{PI} with @code{M_PI} throughout, or put @samp{-DPI=M_PI} +on the compiler command line. @node Trig Functions @section Trigonometric Functions @@ -744,10 +134,10 @@ The arguments to all of these functions are in units of radians; recall that pi radians equals 180 degrees. @cindex pi (trigonometric constant) -The math library does define a symbolic constant for pi in @file{math.h} -(@pxref{Mathematical Constants}) when BSD compliance is required -(@pxref{Feature Test Macros}). In case it is not possible to use this -predefined macro one easily can define it: +The math library normally defines @code{M_PI} to a @code{double} +approximation of pi. If strict ISO and/or POSIX compliance +are requested this constant is not defined, but you can easily define it +yourself: @smallexample #define M_PI 3.14159265358979323846264338327 @@ -757,7 +147,6 @@ predefined macro one easily can define it: You can also compute the value of pi with the expression @code{acos (-1.0)}. - @comment math.h @comment ISO @deftypefun double sin (double @var{x}) @@ -784,22 +173,15 @@ radians. The return value is in the range @code{-1} to @code{1}. These functions return the tangent of @var{x}, where @var{x} is given in radians. -The following @code{errno} error conditions are defined for this function: - -@table @code -@item ERANGE Mathematically, the tangent function has singularities at odd multiples of pi/2. If the argument @var{x} is too close to one of these -singularities, @code{tan} sets @code{errno} to @code{ERANGE} and returns -either positive or negative @code{HUGE_VAL}. -@end table +singularities, @code{tan} will signal overflow. @end deftypefun -In many applications where @code{sin} and @code{cos} are used, the value -for the same argument of both of these functions is used at the same -time. Since the algorithm to compute these values is very similar for -both functions there is an additional function which computes both values -at the same time. +In many applications where @code{sin} and @code{cos} are used, the sine +and cosine of the same angle are needed at the same time. It is more +efficient to compute them simultaneously, so the library provides a +function to do that. @comment math.h @comment GNU @@ -811,33 +193,34 @@ cosine of @var{x} in @code{*@var{cos}}, where @var{x} is given in radians. Both values, @code{*@var{sinx}} and @code{*@var{cosx}}, are in the range of @code{-1} to @code{1}. -This function is a GNU extension. It should be used whenever both sine -and cosine are needed but in portable applications there should be a -fallback method for systems without this function. +This function is a GNU extension. Portable programs should be prepared +to cope with its absence. @end deftypefun @cindex complex trigonometric functions -The trigonometric functions are in mathematics not only defined on real -numbers. They can be extended to complex numbers and the @w{ISO C 9X} -standard introduces these variants in the standard math library. +@w{ISO C 9x} defines variants of the trig functions which work on +complex numbers. The GNU C library provides these functions, but they +are only useful if your compiler supports the new complex types defined +by the standard. +@c Change this when gcc is fixed. -zw +(As of this writing GCC supports complex numbers, but there are bugs in +the implementation.) @comment complex.h @comment ISO @deftypefun {complex double} csin (complex double @var{z}) @deftypefunx {complex float} csinf (complex float @var{z}) @deftypefunx {complex long double} csinl (complex long double @var{z}) -These functions return the complex sine of the complex value in @var{z}. +These functions return the complex sine of @var{z}. The mathematical definition of the complex sine is @ifinfo @math{sin (z) = 1/(2*i) * (exp (z*i) - exp (-z*i))}. @end ifinfo -@iftex @tex $$\sin(z) = {1\over 2i} (e^{zi} - e^{-zi})$$ @end tex -@end iftex @end deftypefun @comment complex.h @@ -845,17 +228,15 @@ $$\sin(z) = {1\over 2i} (e^{zi} - e^{-zi})$$ @deftypefun {complex double} ccos (complex double @var{z}) @deftypefunx {complex float} ccosf (complex float @var{z}) @deftypefunx {complex long double} ccosl (complex long double @var{z}) -These functions return the complex cosine of the complex value in @var{z}. +These functions return the complex cosine of @var{z}. The mathematical definition of the complex cosine is @ifinfo @math{cos (z) = 1/2 * (exp (z*i) + exp (-z*i))} @end ifinfo -@iftex @tex $$\cos(z) = {1\over 2} (e^{zi} + e^{-zi})$$ @end tex -@end iftex @end deftypefun @comment complex.h @@ -863,17 +244,20 @@ $$\cos(z) = {1\over 2} (e^{zi} + e^{-zi})$$ @deftypefun {complex double} ctan (complex double @var{z}) @deftypefunx {complex float} ctanf (complex float @var{z}) @deftypefunx {complex long double} ctanl (complex long double @var{z}) -These functions return the complex tangent of the complex value in @var{z}. +These functions return the complex tangent of @var{z}. The mathematical definition of the complex tangent is @ifinfo -@math{tan (z) = 1/i * (exp (z*i) - exp (-z*i)) / (exp (z*i) + exp (-z*i))} +@math{tan (z) = -i * (exp (z*i) - exp (-z*i)) / (exp (z*i) + exp (-z*i))} @end ifinfo -@iftex @tex -$$\tan(z) = {1\over i} {e^{zi} - e^{-zi}\over e^{zi} + e^{-zi}}$$ +$$\tan(z) = -i \cdot {e^{zi} - e^{-zi}\over e^{zi} + e^{-zi}}$$ @end tex -@end iftex + +@noindent +The complex tangent has poles at @math{pi/2 + 2n}, where @math{n} is an +integer. @code{ctan} may signal overflow if @var{z} is too close to a +pole. @end deftypefun @@ -895,9 +279,9 @@ sine is @var{x}. The value is in units of radians. Mathematically, there are infinitely many such values; the one actually returned is the one between @code{-pi/2} and @code{pi/2} (inclusive). -@code{asin} fails, and sets @code{errno} to @code{EDOM}, if @var{x} is -out of range. The arc sine function is defined mathematically only -over the domain @code{-1} to @code{1}. +The arc sine function is defined mathematically only +over the domain @code{-1} to @code{1}. If @var{x} is outside the +domain, @code{asin} signals a domain error. @end deftypefun @comment math.h @@ -910,12 +294,11 @@ whose cosine is @var{x}. The value is in units of radians. Mathematically, there are infinitely many such values; the one actually returned is the one between @code{0} and @code{pi} (inclusive). -@code{acos} fails, and sets @code{errno} to @code{EDOM}, if @var{x} is -out of range. The arc cosine function is defined mathematically only -over the domain @code{-1} to @code{1}. +The arc cosine function is defined mathematically only +over the domain @code{-1} to @code{1}. If @var{x} is outside the +domain, @code{acos} signals a domain error. @end deftypefun - @comment math.h @comment ISO @deftypefun double atan (double @var{x}) @@ -924,8 +307,7 @@ over the domain @code{-1} to @code{1}. These functions compute the arc tangent of @var{x}---that is, the value whose tangent is @var{x}. The value is in units of radians. Mathematically, there are infinitely many such values; the one actually -returned is the one between @code{-pi/2} and @code{pi/2} -(inclusive). +returned is the one between @code{-pi/2} and @code{pi/2} (inclusive). @end deftypefun @comment math.h @@ -933,11 +315,10 @@ returned is the one between @code{-pi/2} and @code{pi/2} @deftypefun double atan2 (double @var{y}, double @var{x}) @deftypefunx float atan2f (float @var{y}, float @var{x}) @deftypefunx {long double} atan2l (long double @var{y}, long double @var{x}) -This is the two argument arc tangent function. It is similar to computing -the arc tangent of @var{y}/@var{x}, except that the signs of both arguments -are used to determine the quadrant of the result, and @var{x} is -permitted to be zero. The return value is given in radians and is in -the range @code{-pi} to @code{pi}, inclusive. +This function computes the arc tangent of @var{y}/@var{x}, but the signs +of both arguments are used to determine the quadrant of the result, and +@var{x} is permitted to be zero. The return value is given in radians +and is in the range @code{-pi} to @code{pi}, inclusive. If @var{x} and @var{y} are coordinates of a point in the plane, @code{atan2} returns the signed angle between the line from the origin @@ -946,15 +327,12 @@ converting Cartesian coordinates to polar coordinates. (To compute the radial coordinate, use @code{hypot}; see @ref{Exponents and Logarithms}.) -The function @code{atan2} sets @code{errno} to @code{EDOM} if both -@var{x} and @var{y} are zero; the return value is not defined in this -case. +@c This is experimentally true. Should it be so? -zw +If both @var{x} and @var{y} are zero, @code{atan2} returns zero. @end deftypefun @cindex inverse complex trigonometric functions - -The inverse trigonometric functions also exist is separate versions -which are usable with complex numbers. +@w{ISO C 9x} defines complex versions of the inverse trig functions. @comment complex.h @comment ISO @@ -962,10 +340,10 @@ which are usable with complex numbers. @deftypefunx {complex float} casinf (complex float @var{z}) @deftypefunx {complex long double} casinl (complex long double @var{z}) These functions compute the complex arc sine of @var{z}---that is, the -value whose sine is @var{z}. The value is in units of radians. +value whose sine is @var{z}. The value returned is in radians. -Unlike the real version of the arc sine function @code{casin} has no -limitation on the argument @var{z}. +Unlike the real-valued functions, @code{casin} is defined for all +values of @var{z}. @end deftypefun @comment complex.h @@ -974,10 +352,10 @@ limitation on the argument @var{z}. @deftypefunx {complex float} cacosf (complex float @var{z}) @deftypefunx {complex long double} cacosl (complex long double @var{z}) These functions compute the complex arc cosine of @var{z}---that is, the -value whose cosine is @var{z}. The value is in units of radians. +value whose cosine is @var{z}. The value returned is in radians. -Unlike the real version of the arc cosine function @code{cacos} has no -limitation on the argument @var{z}. +Unlike the real-valued functions, @code{cacos} is defined for all +values of @var{z}. @end deftypefun @@ -1002,11 +380,11 @@ the value whose tangent is @var{z}. The value is in units of radians. @deftypefun double exp (double @var{x}) @deftypefunx float expf (float @var{x}) @deftypefunx {long double} expl (long double @var{x}) -These functions return the value of @code{e} (the base of natural -logarithms) raised to power @var{x}. +These functions compute @code{e} (the base of natural logarithms) raised +to the power @var{x}. -The function fails, and sets @code{errno} to @code{ERANGE}, if the -magnitude of the result is too large to be representable. +If the magnitude of the result is too large to be representable, +@code{exp} signals overflow. @end deftypefun @comment math.h @@ -1014,11 +392,8 @@ magnitude of the result is too large to be representable. @deftypefun double exp2 (double @var{x}) @deftypefunx float exp2f (float @var{x}) @deftypefunx {long double} exp2l (long double @var{x}) -These functions return the value of @code{2} raised to the power @var{x}. +These functions compute @code{2} raised to the power @var{x}. Mathematically, @code{exp2 (x)} is the same as @code{exp (x * log (2))}. - -The function fails, and sets @code{errno} to @code{ERANGE}, if the -magnitude of the result is too large to be representable. @end deftypefun @comment math.h @@ -1029,15 +404,11 @@ magnitude of the result is too large to be representable. @deftypefunx double pow10 (double @var{x}) @deftypefunx float pow10f (float @var{x}) @deftypefunx {long double} pow10l (long double @var{x}) -These functions return the value of @code{10} raised to the power @var{x}. -Mathematically, @code{exp2 (x)} is the same as @code{exp (x * log (2))}. +These functions compute @code{10} raised to the power @var{x}. +Mathematically, @code{exp10 (x)} is the same as @code{exp (x * log (10))}. -The function fails, and sets @code{errno} to @code{ERANGE}, if the -magnitude of the result is too large to be representable. - -All these functions are GNU extensions. The name @code{pow10} is used -in some old code but the name @code{exp10} clearly is more in the sense -of the ISO library designers and therefore should probably be preferred. +These functions are GNU extensions. The name @code{exp10} is +preferred, since it is analogous to @code{exp} and @code{exp2}. @end deftypefun @@ -1046,20 +417,13 @@ of the ISO library designers and therefore should probably be preferred. @deftypefun double log (double @var{x}) @deftypefunx float logf (float @var{x}) @deftypefunx {long double} logl (long double @var{x}) -These functions return the natural logarithm of @var{x}. @code{exp (log +These functions compute the natural logarithm of @var{x}. @code{exp (log (@var{x}))} equals @var{x}, exactly in mathematics and approximately in C. -The following @code{errno} error conditions are defined for this function: - -@table @code -@item EDOM -The argument @var{x} is negative. The log function is defined -mathematically to return a real result only on positive arguments. - -@item ERANGE -The argument is zero. The log of zero is not defined. -@end table +If @var{x} is negative, @code{log} signals a domain error. If @var{x} +is zero, it returns negative infinity; if @var{x} is too close to zero, +it may signal overflow. @end deftypefun @comment math.h @@ -1067,9 +431,9 @@ The argument is zero. The log of zero is not defined. @deftypefun double log10 (double @var{x}) @deftypefunx float log10f (float @var{x}) @deftypefunx {long double} log10l (long double @var{x}) -These functions return the base-10 logarithm of @var{x}. Except for the -different base, it is similar to the @code{log} function. In fact, +These functions return the base-10 logarithm of @var{x}. @code{log10 (@var{x})} equals @code{log (@var{x}) / log (10)}. + @end deftypefun @comment math.h @@ -1077,8 +441,7 @@ different base, it is similar to the @code{log} function. In fact, @deftypefun double log2 (double @var{x}) @deftypefunx float log2f (float @var{x}) @deftypefunx {long double} log2l (long double @var{x}) -These functions return the base-2 logarithm of @var{x}. Except for the -different base, it is similar to the @code{log} function. In fact, +These functions return the base-2 logarithm of @var{x}. @code{log2 (@var{x})} equals @code{log (@var{x}) / log (2)}. @end deftypefun @@ -1088,12 +451,13 @@ different base, it is similar to the @code{log} function. In fact, @deftypefunx float logbf (float @var{x}) @deftypefunx {long double} logbl (long double @var{x}) These functions extract the exponent of @var{x} and return it as a -signed integer value. If @var{x} is zero, a range error may occur. +floating-point value. If @code{FLT_RADIX} is two, @code{logb} is equal +to @code{floor (log2 (x))}, except it's probably faster. -A special case are subnormal numbers (if supported by the floating-point -format). The exponent returned is not the actual value from @var{x}. -Instead the number is first normalized as if the range of the exponent -field is large enough. +If @var{x} is denormalized, @code{logb} returns the exponent @var{x} +would have if it were normalized. If @var{x} is infinity (positive or +negative), @code{logb} returns @math{@infinity{}}. If @var{x} is zero, +@code{logb} returns @math{@infinity{}}. It does not signal. @end deftypefun @comment math.h @@ -1102,17 +466,34 @@ field is large enough. @deftypefunx int ilogbf (float @var{x}) @deftypefunx int ilogbl (long double @var{x}) These functions are equivalent to the corresponding @code{logb} -functions except that the values are returned as signed integer values. -Since integer values cannot represent infinity and NaN, there are some -special symbols defined to help detect these situations. - -@vindex FP_ILOGB0 -@vindex FP_ILOGBNAN -@code{ilogb} returns @code{FP_ILOGB0} if @var{x} is @code{0} and it -returns @code{FP_ILOGBNAN} if @var{x} is @code{NaN}. These values are -system specific and no fixed value is assigned. More concrete, these -values might even have the same value. So a piece of code handling the -result of @code{ilogb} could look like this: +functions except that they return signed integer values. +@end deftypefun + +@noindent +Since integers cannot represent infinity and NaN, @code{ilogb} instead +returns an integer that can't be the exponent of a normal floating-point +number. @file{math.h} defines constants so you can check for this. + +@comment math.h +@comment ISO +@deftypevr Macro int FP_ILOGB0 +@code{ilogb} returns this value if its argument is @code{0}. The +numeric value is either @code{INT_MIN} or @code{-INT_MAX}. + +This macro is defined in @w{ISO C 9X}. +@end deftypevr + +@comment math.h +@comment ISO +@deftypevr Macro int FP_ILOGBNAN +@code{ilogb} returns this value if its argument is @code{NaN}. The +numeric value is either @code{INT_MIN} or @code{INT_MAX}. + +This macro is defined in @w{ISO C 9X}. +@end deftypevr + +These values are system specific. They might even be the same. The +proper way to test the result of @code{ilogb} is as follows: @smallexample i = ilogb (f); @@ -1134,8 +515,6 @@ if (i == FP_ILOGB0 || i == FP_ILOGBNAN) @} @end smallexample -@end deftypefun - @comment math.h @comment ISO @deftypefun double pow (double @var{base}, double @var{power}) @@ -1144,17 +523,10 @@ if (i == FP_ILOGB0 || i == FP_ILOGBNAN) These are general exponentiation functions, returning @var{base} raised to @var{power}. -@need 250 -The following @code{errno} error conditions are defined for this function: - -@table @code -@item EDOM -The argument @var{base} is negative and @var{power} is not an integral -value. Mathematically, the result would be a complex number in this case. - -@item ERANGE -An underflow or overflow condition was detected in the result. -@end table +Mathematically, @code{pow} would return a complex number when @var{base} +is negative and @var{power} is not an integral value. @code{pow} can't +do that, so instead it signals a domain error. @code{pow} may also +underflow or overflow the destination type. @end deftypefun @cindex square root function @@ -1165,10 +537,8 @@ An underflow or overflow condition was detected in the result. @deftypefunx {long double} sqrtl (long double @var{x}) These functions return the nonnegative square root of @var{x}. -The @code{sqrt} function fails, and sets @code{errno} to @code{EDOM}, if -@var{x} is negative. Mathematically, the square root would be a complex -number. -@c (@pxref{csqrt}) +If @var{x} is negative, @code{sqrt} signals a domain error. +Mathematically, it should return a complex number. @end deftypefun @cindex cube root function @@ -1187,10 +557,10 @@ fail; every representable real value has a representable real cube root. @deftypefunx float hypotf (float @var{x}, float @var{y}) @deftypefunx {long double} hypotl (long double @var{x}, long double @var{y}) These functions return @code{sqrt (@var{x}*@var{x} + -@var{y}*@var{y})}. (This is the length of the hypotenuse of a right +@var{y}*@var{y})}. This is the length of the hypotenuse of a right triangle with sides of length @var{x} and @var{y}, or the distance -of the point (@var{x}, @var{y}) from the origin.) Using this function -instead of the direct formula is highly appreciated since the error is +of the point (@var{x}, @var{y}) from the origin. Using this function +instead of the direct formula is wise, since the error is much smaller. See also the function @code{cabs} in @ref{Absolute Value}. @end deftypefun @@ -1200,7 +570,7 @@ much smaller. See also the function @code{cabs} in @ref{Absolute Value}. @deftypefunx float expm1f (float @var{x}) @deftypefunx {long double} expm1l (long double @var{x}) These functions return a value equivalent to @code{exp (@var{x}) - 1}. -It is computed in a way that is accurate even if the value of @var{x} is +They are computed in a way that is accurate even if @var{x} is near zero---a case where @code{exp (@var{x}) - 1} would be inaccurate due to subtraction of two numbers that are nearly equal. @end deftypefun @@ -1210,39 +580,32 @@ to subtraction of two numbers that are nearly equal. @deftypefun double log1p (double @var{x}) @deftypefunx float log1pf (float @var{x}) @deftypefunx {long double} log1pl (long double @var{x}) -This function returns a value equivalent to @w{@code{log (1 + @var{x})}}. -It is computed in a way that is accurate even if the value of @var{x} is +These functions returns a value equivalent to @w{@code{log (1 + @var{x})}}. +They are computed in a way that is accurate even if @var{x} is near zero. @end deftypefun @cindex complex exponentiation functions @cindex complex logarithm functions -@w{ISO C 9X} defines variants of some of the exponentiation and -logarithm functions. As for the other functions handling complex -numbers these functions are perhaps better optimized and provide better -error checking than a direct use of the formulas of the mathematical -definition. +@w{ISO C 9X} defines complex variants of some of the exponentiation and +logarithm functions. @comment complex.h @comment ISO @deftypefun {complex double} cexp (complex double @var{z}) @deftypefunx {complex float} cexpf (complex float @var{z}) @deftypefunx {complex long double} cexpl (complex long double @var{z}) -These functions return the value of @code{e} (the base of natural -logarithms) raised to power of the complex value @var{z}. - -@noindent +These functions return @code{e} (the base of natural +logarithms) raised to the power of @var{z}. Mathematically this corresponds to the value @ifinfo @math{exp (z) = exp (creal (z)) * (cos (cimag (z)) + I * sin (cimag (z)))} @end ifinfo -@iftex @tex -$$\exp(z) = e^z = e^{{\rm Re} z} (\cos ({\rm Im} z) + i \sin ({\rm Im} z))$$ +$$\exp(z) = e^z = e^{{\rm Re}\,z} (\cos ({\rm Im}\,z) + i \sin ({\rm Im}\,z))$$ @end tex -@end iftex @end deftypefun @comment complex.h @@ -1250,21 +613,20 @@ $$\exp(z) = e^z = e^{{\rm Re} z} (\cos ({\rm Im} z) + i \sin ({\rm Im} z))$$ @deftypefun {complex double} clog (complex double @var{z}) @deftypefunx {complex float} clogf (complex float @var{z}) @deftypefunx {complex long double} clogl (complex long double @var{z}) -These functions return the natural logarithm of the complex value -@var{z}. Unlike the real value version @code{log} and its variants, -@code{clog} has no limit for the range of its argument @var{z}. - -@noindent +These functions return the natural logarithm of @var{z}. Mathematically this corresponds to the value @ifinfo @math{log (z) = log (cabs (z)) + I * carg (z)} @end ifinfo -@iftex @tex -$$\log(z) = \log(|z|) + i \arg(z)$$ +$$\log(z) = \log |z| + i \arg z$$ @end tex -@end iftex + +@noindent +@code{clog} has a pole at 0, and will signal overflow if @var{z} equals +or is very close to 0. It is well-defined for all other values of +@var{z}. @end deftypefun @@ -1274,22 +636,16 @@ $$\log(z) = \log(|z|) + i \arg(z)$$ @deftypefunx {complex float} clog10f (complex float @var{z}) @deftypefunx {complex long double} clog10l (complex long double @var{z}) These functions return the base 10 logarithm of the complex value -@var{z}. Unlike the real value version @code{log} and its variants, -@code{clog} has no limit for the range of its argument @var{z}. - -@noindent -Mathematically this corresponds to the value +@var{z}. Mathematically this corresponds to the value @ifinfo @math{log (z) = log10 (cabs (z)) + I * carg (z)} @end ifinfo -@iftex @tex -$$\log_{10}(z) = \log_{10}(|z|) + i \arg(z)$$ +$$\log_{10}(z) = \log_{10}|z| + i \arg z$$ @end tex -@end iftex -This function is a GNU extension. +These functions are GNU extensions. @end deftypefun @comment complex.h @@ -1297,9 +653,8 @@ This function is a GNU extension. @deftypefun {complex double} csqrt (complex double @var{z}) @deftypefunx {complex float} csqrtf (complex float @var{z}) @deftypefunx {complex long double} csqrtl (complex long double @var{z}) -These functions return the complex root of the argument @var{z}. Unlike -the @code{sqrt} function these functions do not have any restriction on -the value of the argument. +These functions return the complex square root of the argument @var{z}. Unlike +the real-valued functions, they are defined for all values of @var{z}. @end deftypefun @comment complex.h @@ -1307,20 +662,10 @@ the value of the argument. @deftypefun {complex double} cpow (complex double @var{base}, complex double @var{power}) @deftypefunx {complex float} cpowf (complex float @var{base}, complex float @var{power}) @deftypefunx {complex long double} cpowl (complex long double @var{base}, complex long double @var{power}) -These functions return the complex value @var{base} raised to the power of -@var{power}. This is computed as - -@ifinfo -@math{cpow (x, y) = cexp (y * clog (x))} -@end ifinfo -@iftex -@tex -$${\rm cpow}(x, y) = e^{y \log(x)}$$ -@end tex -@end iftex +These functions return @var{base} raised to the power of +@var{power}. This is equivalent to @w{@code{cexp (y * clog (x))}} @end deftypefun - @node Hyperbolic Functions @section Hyperbolic Functions @cindex hyperbolic functions @@ -1334,9 +679,8 @@ see @ref{Exponents and Logarithms}. @deftypefunx float sinhf (float @var{x}) @deftypefunx {long double} sinhl (long double @var{x}) These functions return the hyperbolic sine of @var{x}, defined -mathematically as @w{@code{(exp (@var{x}) - exp (-@var{x})) / 2}}. The -function fails, and sets @code{errno} to @code{ERANGE}, if the value of -@var{x} is too large; that is, if overflow occurs. +mathematically as @w{@code{(exp (@var{x}) - exp (-@var{x})) / 2}}. They +may signal overflow if @var{x} is too large. @end deftypefun @comment math.h @@ -1346,8 +690,7 @@ function fails, and sets @code{errno} to @code{ERANGE}, if the value of @deftypefunx {long double} coshl (long double @var{x}) These function return the hyperbolic cosine of @var{x}, defined mathematically as @w{@code{(exp (@var{x}) + exp (-@var{x})) / 2}}. -The function fails, and sets @code{errno} to @code{ERANGE}, if the value -of @var{x} is too large; that is, if overflow occurs. +They may signal overflow if @var{x} is too large. @end deftypefun @comment math.h @@ -1355,16 +698,15 @@ of @var{x} is too large; that is, if overflow occurs. @deftypefun double tanh (double @var{x}) @deftypefunx float tanhf (float @var{x}) @deftypefunx {long double} tanhl (long double @var{x}) -These functions return the hyperbolic tangent of @var{x}, whose -mathematical definition is @w{@code{sinh (@var{x}) / cosh (@var{x})}}. +These functions return the hyperbolic tangent of @var{x}, +defined mathematically as @w{@code{sinh (@var{x}) / cosh (@var{x})}}. +They may signal overflow if @var{x} is too large. @end deftypefun @cindex hyperbolic functions -There are counterparts for these hyperbolic functions which work with -complex valued arguments. They should always be used instead of the -obvious mathematical formula since the implementations in the math -library are optimized for accuracy and speed. +There are counterparts for the hyperbolic functions which take +complex arguments. @comment complex.h @comment ISO @@ -1372,9 +714,7 @@ library are optimized for accuracy and speed. @deftypefunx {complex float} csinhf (complex float @var{z}) @deftypefunx {complex long double} csinhl (complex long double @var{z}) These functions return the complex hyperbolic sine of @var{z}, defined -mathematically as @w{@code{(exp (@var{z}) - exp (-@var{z})) / 2}}. The -function fails, and sets @code{errno} to @code{ERANGE}, if the value of -result is too large. +mathematically as @w{@code{(exp (@var{z}) - exp (-@var{z})) / 2}}. @end deftypefun @comment complex.h @@ -1383,9 +723,7 @@ result is too large. @deftypefunx {complex float} ccoshf (complex float @var{z}) @deftypefunx {complex long double} ccoshl (complex long double @var{z}) These functions return the complex hyperbolic cosine of @var{z}, defined -mathematically as @w{@code{(exp (@var{z}) + exp (-@var{z})) / 2}}. The -function fails, and sets @code{errno} to @code{ERANGE}, if the value of -result is too large. +mathematically as @w{@code{(exp (@var{z}) + exp (-@var{z})) / 2}}. @end deftypefun @comment complex.h @@ -1393,8 +731,8 @@ result is too large. @deftypefun {complex double} ctanh (complex double @var{z}) @deftypefunx {complex float} ctanhf (complex float @var{z}) @deftypefunx {complex long double} ctanhl (complex long double @var{z}) -These functions return the complex hyperbolic tangent of @var{z}, whose -mathematical definition is @w{@code{csinh (@var{z}) / ccosh (@var{z})}}. +These functions return the complex hyperbolic tangent of @var{z}, +defined mathematically as @w{@code{csinh (@var{z}) / ccosh (@var{z})}}. @end deftypefun @@ -1416,7 +754,7 @@ value whose hyperbolic sine is @var{x}. @deftypefunx {long double} acoshl (long double @var{x}) These functions return the inverse hyperbolic cosine of @var{x}---the value whose hyperbolic cosine is @var{x}. If @var{x} is less than -@code{1}, @code{acosh} returns @code{HUGE_VAL}. +@code{1}, @code{acosh} signals a domain error. @end deftypefun @comment math.h @@ -1426,8 +764,8 @@ value whose hyperbolic cosine is @var{x}. If @var{x} is less than @deftypefunx {long double} atanhl (long double @var{x}) These functions return the inverse hyperbolic tangent of @var{x}---the value whose hyperbolic tangent is @var{x}. If the absolute value of -@var{x} is greater than or equal to @code{1}, @code{atanh} returns -@code{HUGE_VAL}. +@var{x} is greater than @code{1}, @code{atanh} signals a domain error; +if it is equal to 1, @code{atanh} returns infinity. @end deftypefun @cindex inverse complex hyperbolic functions @@ -1448,8 +786,7 @@ These functions return the inverse complex hyperbolic sine of @deftypefunx {complex long double} cacoshl (complex long double @var{z}) These functions return the inverse complex hyperbolic cosine of @var{z}---the value whose complex hyperbolic cosine is @var{z}. Unlike -the real valued function @code{acosh} there is not limit for the range -of the argument. +the real-valued functions, there are no restrictions on the value of @var{z}. @end deftypefun @comment complex.h @@ -1459,10 +796,157 @@ of the argument. @deftypefunx {complex long double} catanhl (complex long double @var{z}) These functions return the inverse complex hyperbolic tangent of @var{z}---the value whose complex hyperbolic tangent is @var{z}. Unlike -the real valued function @code{atanh} there is not limit for the range -of the argument. +the real-valued functions, there are no restrictions on the value of +@var{z}. @end deftypefun +@node Special Functions +@section Special Functions +@cindex special functions +@cindex Bessel functions +@cindex gamma function + +These are some more exotic mathematical functions, which are sometimes +useful. Currently they only have real-valued versions. + +@comment math.h +@comment SVID +@deftypefun double erf (double @var{x}) +@deftypefunx float erff (float @var{x}) +@deftypefunx {long double} erfl (long double @var{x}) +@code{erf} returns the error function of @var{x}. The error +function is defined as +@tex +$$\hbox{erf}(x) = {2\over\sqrt{\pi}}\cdot\int_0^x e^{-t^2} \hbox{d}t$$ +@end tex +@ifnottex +@smallexample +erf (x) = 2/sqrt(pi) * integral from 0 to x of exp(-t^2) dt +@end smallexample +@end ifnottex +@end deftypefun + +@comment math.h +@comment SVID +@deftypefun double erfc (double @var{x}) +@deftypefunx float erfcf (float @var{x}) +@deftypefunx {long double} erfcl (long double @var{x}) +@code{erfc} returns @code{1.0 - erf(@var{x})}, but computed in a +fashion that avoids round-off error when @var{x} is large. +@end deftypefun + +@comment math.h +@comment SVID +@deftypefun double lgamma (double @var{x}) +@deftypefunx float lgammaf (float @var{x}) +@deftypefunx {long double} lgammal (long double @var{x}) +@code{lgamma} returns the natural logarithm of the absolute value of +the gamma function of @var{x}. The gamma function is defined as +@tex +$$\Gamma(x) = \int_0^\infty t^{x-1} e^{-t} \hbox{d}t$$ +@end tex +@ifnottex +@smallexample +gamma (x) = integral from 0 to @infinity{} of t^(x-1) e^-t dt +@end smallexample +@end ifnottex + +@vindex signgam +The sign of the gamma function is stored in the global variable +@var{signgam}, which is declared in @file{math.h}. It is @code{1} if +the intermediate result was positive or zero, and, @code{-1} if it was +negative. + +You can compute the actual gamma function as follows: +@smallexample +lgam = lgamma(x); +gam = signgam*exp(lgam); +@end smallexample + +The gamma function has singularities at the nonpositive integers. +@code{lgamma} will raise the zero divide exception if evaluated at a +singularity. +@end deftypefun + +@comment math.h +@comment XPG +@deftypefun double lgamma_r (double @var{x}) +@deftypefunx float lgammaf_r (float @var{x}) +@deftypefunx {long double} lgammal_r (long double @var{x}) +@code{lgamma_r} is just like @code{lgamma}, but it stores the sign of +the intermediate result in the variable pointed to by @var{signp} +instead of in the @var{signgam} global. +@end deftypefun + +@ignore +@comment math.h +@comment SVID +@deftypefun double gamma (double @var{x}) +@deftypefunx float gammaf (float @var{x}) +@deftypefunx {long double} gammal (long double @var{x}) +??? _not_ exp(lgamma())*signgam - historical? +@end deftypefun +@end ignore + +@comment math.h +@comment SVID +@deftypefun double j0 (double @var{x}) +@deftypefunx float j0f (float @var{x}) +@deftypefunx {long double} j0l (long double @var{x}) +@code{j0} returns the Bessel function of the first kind of order 0 of +@var{x}. It may signal underflow if @var{x} is too large. +@end deftypefun + +@comment math.h +@comment SVID +@deftypefun double j1 (double @var{x}) +@deftypefunx float j1f (float @var{x}) +@deftypefunx {long double} j1l (long double @var{x}) +@code{j1} returns the Bessel function of the first kind of order 1 of +@var{x}. It may signal underflow if @var{x} is too large. +@end deftypefun + +@comment math.h +@comment SVID +@deftypefun double jn (int n, double @var{x}) +@deftypefunx float jnf (int n, float @var{x}) +@deftypefunx {long double} jnl (int n, long double @var{x}) +@code{jn} returns the Bessel function of the first kind of order +@var{n} of @var{x}. It may signal underflow if @var{x} is too large. +@end deftypefun + +@comment math.h +@comment SVID +@deftypefun double y0 (double @var{x}) +@deftypefunx float y0f (float @var{x}) +@deftypefunx {long double} y0l (long double @var{x}) +@code{y0} returns the Bessel function of the second kind of order 0 of +@var{x}. It may signal underflow if @var{x} is too large. If @var{x} +is negative, @code{y0} signals a domain error; if it is zero, +@code{y0} signals overflow and returns @math{-@infinity}. +@end deftypefun + +@comment math.h +@comment SVID +@deftypefun double y1 (double @var{x}) +@deftypefunx float y1f (float @var{x}) +@deftypefunx {long double} y1l (long double @var{x}) +@code{y1} returns the Bessel function of the second kind of order 1 of +@var{x}. It may signal underflow if @var{x} is too large. If @var{x} +is negative, @code{y1} signals a domain error; if it is zero, +@code{y1} signals overflow and returns @math{-@infinity}. +@end deftypefun + +@comment math.h +@comment SVID +@deftypefun double yn (int n, double @var{x}) +@deftypefunx float ynf (int n, float @var{x}) +@deftypefunx {long double} ynl (int n, long double @var{x}) +@code{yn} returns the Bessel function of the second kind of order @var{n} of +@var{x}. It may signal underflow if @var{x} is too large. If @var{x} +is negative, @code{yn} signals a domain error; if it is zero, +@code{yn} signals overflow and returns @math{-@infinity}. +@end deftypefun @node Pseudo-Random Numbers @section Pseudo-Random Numbers @@ -1472,19 +956,19 @@ of the argument. This section describes the GNU facilities for generating a series of pseudo-random numbers. The numbers generated are not truly random; -typically, they form a sequence that repeats periodically, with a -period so large that you can ignore it for ordinary purposes. The -random number generator works by remembering at all times a @dfn{seed} -value which it uses to compute the next random number and also to -compute a new seed. +typically, they form a sequence that repeats periodically, with a period +so large that you can ignore it for ordinary purposes. The random +number generator works by remembering a @dfn{seed} value which it uses +to compute the next random number and also to compute a new seed. Although the generated numbers look unpredictable within one run of a program, the sequence of numbers is @emph{exactly the same} from one run to the next. This is because the initial seed is always the same. This is convenient when you are debugging a program, but it is unhelpful if -you want the program to behave unpredictably. If you want truly random -numbers, not just pseudo-random, specify a seed based on the current -time. +you want the program to behave unpredictably. If you want a different +pseudo-random series each time your program runs, you must specify a +different seed each time. For ordinary purposes, basing the seed on the +current time works well. You can get repeatable sequences of numbers on a particular machine type by specifying the same initial seed value for the random number @@ -1493,19 +977,20 @@ the same seed, used in different C libraries or on different CPU types, will give you different random numbers. The GNU library supports the standard @w{ISO C} random number functions -plus two other sets derived from BSD and SVID. We recommend you use the -standard ones, @code{rand} and @code{srand} if only a small number of -random bits are required. The SVID functions provide an interface which -allows better random number generator algorithms and they return up to -48 random bits in one calls and they also return random floating-point -numbers if wanted. The SVID function might not be available on some BSD -derived systems but since they are required in the XPG they are -available on all Unix-conformant systems. +plus two other sets derived from BSD and SVID. The BSD and @w{ISO C} +functions provide identical, somewhat limited functionality. If only a +small number of random bits are required, we recommend you use the +@w{ISO C} interface, @code{rand} and @code{srand}. The SVID functions +provide a more flexible interface, which allows better random number +generator algorithms, provides more random bits (up to 48) per call, and +can provide random floating-point numbers. These functions are required +by the XPG standard and therefore will be present in all modern Unix +systems. @menu -* ISO Random:: @code{rand} and friends. -* BSD Random:: @code{random} and friends. -* SVID Random:: @code{drand48} and friends. +* ISO Random:: @code{rand} and friends. +* BSD Random:: @code{random} and friends. +* SVID Random:: @code{drand48} and friends. @end menu @node ISO Random @@ -1521,18 +1006,17 @@ To use these facilities, you should include the header file @comment stdlib.h @comment ISO @deftypevr Macro int RAND_MAX -The value of this macro is an integer constant expression that -represents the maximum possible value returned by the @code{rand} -function. In the GNU library, it is @code{037777777}, which is the -largest signed integer representable in 32 bits. In other libraries, it -may be as low as @code{32767}. +The value of this macro is an integer constant representing the largest +value the @code{rand} function can return. In the GNU library, it is +@code{2147483647}, which is the largest signed integer representable in +32 bits. In other libraries, it may be as low as @code{32767}. @end deftypevr @comment stdlib.h @comment ISO @deftypefun int rand (void) The @code{rand} function returns the next pseudo-random number in the -series. The value is in the range from @code{0} to @code{RAND_MAX}. +series. The value ranges from @code{0} to @code{RAND_MAX}. @end deftypefun @comment stdlib.h @@ -1543,31 +1027,27 @@ pseudo-random numbers. If you call @code{rand} before a seed has been established with @code{srand}, it uses the value @code{1} as a default seed. -To produce truly random numbers (not just pseudo-random), do @code{srand -(time (0))}. +To produce a different pseudo-random series each time your program is +run, do @code{srand (time (0))}. @end deftypefun -A completely broken interface was designed by the POSIX.1 committee to -support reproducible random numbers in multi-threaded programs. +POSIX.1 extended the C standard functions to support reproducible random +numbers in multi-threaded programs. However, the extension is badly +designed and unsuitable for serious work. @comment stdlib.h @comment POSIX.1 @deftypefun int rand_r (unsigned int *@var{seed}) This function returns a random number in the range 0 to @code{RAND_MAX} -just as @code{rand} does. But this function does not keep an internal -state for the RNG. Instead the @code{unsigned int} variable pointed to -by the argument @var{seed} is the only state. Before the value is -returned the state will be updated so that the next call will return a -new number. - -I.e., the state of the RNG can only have as much bits as the type -@code{unsigned int} has. This is far too few to provide a good RNG. -This interface is broken by design. +just as @code{rand} does. However, all its state is stored in the +@var{seed} argument. This means the RNG's state can only have as many +bits as the type @code{unsigned int} has. This is far too few to +provide a good RNG. -If the program requires reproducible random numbers in multi-threaded -programs the reentrant SVID functions are probably a better choice. But -these functions are GNU extensions and therefore @code{rand_r}, as being -standardized in POSIX.1, should always be kept as a default method. +If your program requires a reentrant RNG, we recommend you use the +reentrant GNU extensions to the SVID random number generator. The +POSIX.1 interface should only be used when the GNU extensions are not +available. @end deftypefun @@ -1585,24 +1065,24 @@ The prototypes for these functions are in @file{stdlib.h}. @comment BSD @deftypefun {int32_t} random (void) This function returns the next pseudo-random number in the sequence. -The range of values returned is from @code{0} to @code{RAND_MAX}. +The value returned ranges from @code{0} to @code{RAND_MAX}. -@strong{Please note:} Historically this function returned a @code{long -int} value. But with the appearance of 64bit machines this could lead -to severe compatibility problems and therefore the type now explicitly -limits the return value to 32bit. +@strong{Note:} Historically this function returned a @code{long +int} value. On 64bit systems @code{long int} would have been larger +than programs expected, so @code{random} is now defined to return +exactly 32 bits. @end deftypefun @comment stdlib.h @comment BSD @deftypefun void srandom (unsigned int @var{seed}) -The @code{srandom} function sets the seed for the current random number -state based on the integer @var{seed}. If you supply a @var{seed} value +The @code{srandom} function sets the state of the random number +generator based on the integer @var{seed}. If you supply a @var{seed} value of @code{1}, this will cause @code{random} to reproduce the default set of random numbers. -To produce truly random numbers (not just pseudo-random), do -@code{srandom (time (0))}. +To produce a different set of pseudo-random numbers each time your +program runs, do @code{srandom (time (0))}. @end deftypefun @comment stdlib.h @@ -1610,9 +1090,9 @@ To produce truly random numbers (not just pseudo-random), do @deftypefun {void *} initstate (unsigned int @var{seed}, void *@var{state}, size_t @var{size}) The @code{initstate} function is used to initialize the random number generator state. The argument @var{state} is an array of @var{size} -bytes, used to hold the state information. The size must be at least 8 -bytes, and optimal sizes are 8, 16, 32, 64, 128, and 256. The bigger -the @var{state} array, the better. +bytes, used to hold the state information. It is initialized based on +@var{seed}. The size must be between 8 and 256 bytes, and should be a +power of two. The bigger the @var{state} array, the better. The return value is the previous value of the state information array. You can use this value later as an argument to @code{setstate} to @@ -1631,13 +1111,12 @@ You can use this value later as an argument to @code{setstate} to restore that state. @end deftypefun - @node SVID Random @subsection SVID Random Number Function The C library on SVID systems contains yet another kind of random number generator functions. They use a state of 48 bits of data. The user can -choose among a collection of functions which all return the random bits +choose among a collection of functions which return the random bits in different forms. Generally there are two kinds of functions: those which use a state of @@ -1973,3 +1452,37 @@ If the return value is non-negative the function call succeeded. This function is a GNU extension and should not be used in portable programs. @end deftypefun + +@node FP Function Optimizations +@section Is Fast Code or Small Code preferred? +@cindex Optimization + +If an application uses many floating point function it is often the case +that the costs for the function calls itselfs are not neglectable. +Modern processor implementation often can execute the operation itself +very fast but the call means a disturbance of the control flow. + +For this reason the GNU C Library provides optimizations for many of the +frequently used math functions. When the GNU CC is used and the user +activates the optimizer several new inline functions and macros get +defined. These new functions and macros have the same names as the +library function and so get used instead of the later. In case of +inline functions the compiler will decide whether it is reasonable to +use the inline function and this decision is usually correct. + +For the generated code this means that no calls to the library functions +are necessary. This increases the speed significantly. But the +drawback is that the code size increases and this increase is not always +neglectable. + +In cases where the inline functions and macros are not wanted the symbol +@code{__NO_MATH_INLINES} should be defined before any system header is +included. This will make sure only library functions are used. Of +course it can be determined for each single file in the project whether +giving this option is preferred or not. + +Not all hardware implements the entire @w{IEEE 754} standard, or if it +does, there may be a substantial performance penalty for using some of +its features. For example, enabling traps on some processors forces +the FPU to run unpipelined, which more than doubles calculation time. +@c ***Add explanation of -lieee, -mieee. |