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-rw-r--r--sysdeps/powerpc/fpu/w_sqrt.c143
1 files changed, 24 insertions, 119 deletions
diff --git a/sysdeps/powerpc/fpu/w_sqrt.c b/sysdeps/powerpc/fpu/w_sqrt.c
index ff0331725c..806d8e4907 100644
--- a/sysdeps/powerpc/fpu/w_sqrt.c
+++ b/sysdeps/powerpc/fpu/w_sqrt.c
@@ -1,5 +1,5 @@
-/* Double-precision floating point square root.
- Copyright (C) 1997, 2002, 2003 Free Software Foundation, Inc.
+/* Double-precision floating point square root wrapper.
+ Copyright (C) 2004 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -17,130 +17,35 @@
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
-#include <math.h>
-#include <math_private.h>
+#include "math.h"
+#include "math_private.h"
#include <fenv_libc.h>
-#include <inttypes.h>
-static const double almost_half = 0.5000000000000001; /* 0.5 + 2^-53 */
-static const ieee_float_shape_type a_nan = { .word = 0x7fc00000 };
-static const ieee_float_shape_type a_inf = { .word = 0x7f800000 };
-static const float two108 = 3.245185536584267269e+32;
-static const float twom54 = 5.551115123125782702e-17;
-extern const float __t_sqrt[1024];
-
-/* The method is based on a description in
- Computation of elementary functions on the IBM RISC System/6000 processor,
- P. W. Markstein, IBM J. Res. Develop, 34(1) 1990.
- Basically, it consists of two interleaved Newton-Rhapson approximations,
- one to find the actual square root, and one to find its reciprocal
- without the expense of a division operation. The tricky bit here
- is the use of the POWER/PowerPC multiply-add operation to get the
- required accuracy with high speed.
-
- The argument reduction works by a combination of table lookup to
- obtain the initial guesses, and some careful modification of the
- generated guesses (which mostly runs on the integer unit, while the
- Newton-Rhapson is running on the FPU). */
+#ifdef __STDC__
double
-__sqrt(double x)
-{
- const float inf = a_inf.value;
- /* x = f_wash(x); *//* This ensures only one exception for SNaN. */
- if (x > 0)
- {
- if (x != inf)
- {
- /* Variables named starting with 's' exist in the
- argument-reduced space, so that 2 > sx >= 0.5,
- 1.41... > sg >= 0.70.., 0.70.. >= sy > 0.35... .
- Variables named ending with 'i' are integer versions of
- floating-point values. */
- double sx; /* The value of which we're trying to find the
- square root. */
- double sg,g; /* Guess of the square root of x. */
- double sd,d; /* Difference between the square of the guess and x. */
- double sy; /* Estimate of 1/2g (overestimated by 1ulp). */
- double sy2; /* 2*sy */
- double e; /* Difference between y*g and 1/2 (se = e * fsy). */
- double shx; /* == sx * fsg */
- double fsg; /* sg*fsg == g. */
- fenv_t fe; /* Saved floating-point environment (stores rounding
- mode and whether the inexact exception is
- enabled). */
- uint32_t xi0, xi1, sxi, fsgi;
- const float *t_sqrt;
-
- fe = fegetenv_register();
- EXTRACT_WORDS (xi0,xi1,x);
- relax_fenv_state();
- sxi = (xi0 & 0x3fffffff) | 0x3fe00000;
- INSERT_WORDS (sx, sxi, xi1);
- t_sqrt = __t_sqrt + (xi0 >> (52-32-8-1) & 0x3fe);
- sg = t_sqrt[0];
- sy = t_sqrt[1];
-
- /* Here we have three Newton-Rhapson iterations each of a
- division and a square root and the remainder of the
- argument reduction, all interleaved. */
- sd = -(sg*sg - sx);
- fsgi = (xi0 + 0x40000000) >> 1 & 0x7ff00000;
- sy2 = sy + sy;
- sg = sy*sd + sg; /* 16-bit approximation to sqrt(sx). */
- INSERT_WORDS (fsg, fsgi, 0);
- e = -(sy*sg - almost_half);
- sd = -(sg*sg - sx);
- if ((xi0 & 0x7ff00000) == 0)
- goto denorm;
- sy = sy + e*sy2;
- sg = sg + sy*sd; /* 32-bit approximation to sqrt(sx). */
- sy2 = sy + sy;
- e = -(sy*sg - almost_half);
- sd = -(sg*sg - sx);
- sy = sy + e*sy2;
- shx = sx * fsg;
- sg = sg + sy*sd; /* 64-bit approximation to sqrt(sx),
- but perhaps rounded incorrectly. */
- sy2 = sy + sy;
- g = sg * fsg;
- e = -(sy*sg - almost_half);
- d = -(g*sg - shx);
- sy = sy + e*sy2;
- fesetenv_register (fe);
- return g + sy*d;
- denorm:
- /* For denormalised numbers, we normalise, calculate the
- square root, and return an adjusted result. */
- fesetenv_register (fe);
- return __sqrt(x * two108) * twom54;
- }
- }
- else if (x < 0)
- {
-#ifdef FE_INVALID_SQRT
- feraiseexcept (FE_INVALID_SQRT);
- /* For some reason, some PowerPC processors don't implement
- FE_INVALID_SQRT. I guess no-one ever thought they'd be
- used for square roots... :-) */
- if (!fetestexcept (FE_INVALID))
+__sqrt (double x) /* wrapper sqrt */
+#else
+double
+__sqrt (x) /* wrapper sqrt */
+ double x;
#endif
- feraiseexcept (FE_INVALID);
-#ifndef _IEEE_LIBM
- if (_LIB_VERSION != _IEEE_)
- x = __kernel_standard(x,x,26);
- else
+{
+#ifdef _IEEE_LIBM
+ return __ieee754_sqrt (x);
+#else
+ double z;
+ z = __ieee754_sqrt (x);
+ if (_LIB_VERSION == _IEEE_ || (x != x))
+ return z;
+
+ if (x < 0.0)
+ return __kernel_standard (x, x, 26); /* sqrt(negative) */
+ else
+ return z;
#endif
- x = a_nan.value;
- }
- return f_wash(x);
}
weak_alias (__sqrt, sqrt)
-/* Strictly, this is wrong, but the only places where _ieee754_sqrt is
- used will not pass in a negative result. */
-strong_alias(__sqrt,__ieee754_sqrt)
-
#ifdef NO_LONG_DOUBLE
-weak_alias (__sqrt, __sqrtl)
-weak_alias (__sqrt, sqrtl)
+ strong_alias (__sqrt, __sqrtl) weak_alias (__sqrt, sqrtl)
#endif