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Diffstat (limited to 'sysdeps/libm-ieee754/s_log2.c')
| -rw-r--r-- | sysdeps/libm-ieee754/s_log2.c | 136 |
1 files changed, 0 insertions, 136 deletions
diff --git a/sysdeps/libm-ieee754/s_log2.c b/sysdeps/libm-ieee754/s_log2.c deleted file mode 100644 index 7379ce85e7..0000000000 --- a/sysdeps/libm-ieee754/s_log2.c +++ /dev/null @@ -1,136 +0,0 @@ -/* Adapted for log2 by Ulrich Drepper <drepper@cygnus.com>. */ -/* - * ==================================================== - * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. - * - * Developed at SunPro, a Sun Microsystems, Inc. business. - * Permission to use, copy, modify, and distribute this - * software is freely granted, provided that this notice - * is preserved. - * ==================================================== - */ - -/* __log2(x) - * Return the logarithm to base 2 of x - * - * Method : - * 1. Argument Reduction: find k and f such that - * x = 2^k * (1+f), - * where sqrt(2)/2 < 1+f < sqrt(2) . - * - * 2. Approximation of log(1+f). - * Let s = f/(2+f) ; based on log(1+f) = log(1+s) - log(1-s) - * = 2s + 2/3 s**3 + 2/5 s**5 + ....., - * = 2s + s*R - * We use a special Reme algorithm on [0,0.1716] to generate - * a polynomial of degree 14 to approximate R The maximum error - * of this polynomial approximation is bounded by 2**-58.45. In - * other words, - * 2 4 6 8 10 12 14 - * R(z) ~ Lg1*s +Lg2*s +Lg3*s +Lg4*s +Lg5*s +Lg6*s +Lg7*s - * (the values of Lg1 to Lg7 are listed in the program) - * and - * | 2 14 | -58.45 - * | Lg1*s +...+Lg7*s - R(z) | <= 2 - * | | - * Note that 2s = f - s*f = f - hfsq + s*hfsq, where hfsq = f*f/2. - * In order to guarantee error in log below 1ulp, we compute log - * by - * log(1+f) = f - s*(f - R) (if f is not too large) - * log(1+f) = f - (hfsq - s*(hfsq+R)). (better accuracy) - * - * 3. Finally, log(x) = k + log(1+f). - * = k+(f-(hfsq-(s*(hfsq+R)))) - * - * Special cases: - * log2(x) is NaN with signal if x < 0 (including -INF) ; - * log2(+INF) is +INF; log(0) is -INF with signal; - * log2(NaN) is that NaN with no signal. - * - * Constants: - * The hexadecimal values are the intended ones for the following - * constants. The decimal values may be used, provided that the - * compiler will convert from decimal to binary accurately enough - * to produce the hexadecimal values shown. - */ - -#include "math.h" -#include "math_private.h" - -#ifdef __STDC__ -static const double -#else -static double -#endif -ln2 = 0.69314718055994530942, -two54 = 1.80143985094819840000e+16, /* 43500000 00000000 */ -Lg1 = 6.666666666666735130e-01, /* 3FE55555 55555593 */ -Lg2 = 3.999999999940941908e-01, /* 3FD99999 9997FA04 */ -Lg3 = 2.857142874366239149e-01, /* 3FD24924 94229359 */ -Lg4 = 2.222219843214978396e-01, /* 3FCC71C5 1D8E78AF */ -Lg5 = 1.818357216161805012e-01, /* 3FC74664 96CB03DE */ -Lg6 = 1.531383769920937332e-01, /* 3FC39A09 D078C69F */ -Lg7 = 1.479819860511658591e-01; /* 3FC2F112 DF3E5244 */ - -#ifdef __STDC__ -static const double zero = 0.0; -#else -static double zero = 0.0; -#endif - -#ifdef __STDC__ - double __log2(double x) -#else - double __log2(x) - double x; -#endif -{ - double hfsq,f,s,z,R,w,t1,t2,dk; - int32_t k,hx,i,j; - u_int32_t lx; - - EXTRACT_WORDS(hx,lx,x); - - k=0; - if (hx < 0x00100000) { /* x < 2**-1022 */ - if (((hx&0x7fffffff)|lx)==0) - return -two54/(x-x); /* log(+-0)=-inf */ - if (hx<0) return (x-x)/(x-x); /* log(-#) = NaN */ - k -= 54; x *= two54; /* subnormal number, scale up x */ - GET_HIGH_WORD(hx,x); - } - if (hx >= 0x7ff00000) return x+x; - k += (hx>>20)-1023; - hx &= 0x000fffff; - i = (hx+0x95f64)&0x100000; - SET_HIGH_WORD(x,hx|(i^0x3ff00000)); /* normalize x or x/2 */ - k += (i>>20); - dk = (double) k; - f = x-1.0; - if((0x000fffff&(2+hx))<3) { /* |f| < 2**-20 */ - if(f==zero) return dk; - R = f*f*(0.5-0.33333333333333333*f); - return dk-(R-f)/ln2; - } - s = f/(2.0+f); - z = s*s; - i = hx-0x6147a; - w = z*z; - j = 0x6b851-hx; - t1= w*(Lg2+w*(Lg4+w*Lg6)); - t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7))); - i |= j; - R = t2+t1; - if(i>0) { - hfsq=0.5*f*f; - return dk-((hfsq-(s*(hfsq+R)))-f)/ln2; - } else { - return dk-((s*(f-R))-f)/ln2; - } -} - -weak_alias (__log2, log2) -#ifdef NO_LONG_DOUBLE -strong_alias (__log2, __log2l) -weak_alias (__log2, log2l) -#endif |