0,0 → 1,92 |
/* ef_log.c -- float version of e_log.c. |
* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@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. |
* ==================================================== |
*/ |
|
#include "fdlibm.h" |
|
#ifdef __STDC__ |
static const float |
#else |
static float |
#endif |
ln2_hi = 6.9313812256e-01, /* 0x3f317180 */ |
ln2_lo = 9.0580006145e-06, /* 0x3717f7d1 */ |
two25 = 3.355443200e+07, /* 0x4c000000 */ |
Lg1 = 6.6666668653e-01, /* 3F2AAAAB */ |
Lg2 = 4.0000000596e-01, /* 3ECCCCCD */ |
Lg3 = 2.8571429849e-01, /* 3E924925 */ |
Lg4 = 2.2222198546e-01, /* 3E638E29 */ |
Lg5 = 1.8183572590e-01, /* 3E3A3325 */ |
Lg6 = 1.5313838422e-01, /* 3E1CD04F */ |
Lg7 = 1.4798198640e-01; /* 3E178897 */ |
|
#ifdef __STDC__ |
static const float zero = 0.0; |
#else |
static float zero = 0.0; |
#endif |
|
#ifdef __STDC__ |
float __ieee754_logf(float x) |
#else |
float __ieee754_logf(x) |
float x; |
#endif |
{ |
float hfsq,f,s,z,R,w,t1,t2,dk; |
__int32_t k,ix,i,j; |
|
GET_FLOAT_WORD(ix,x); |
|
k=0; |
if (FLT_UWORD_IS_ZERO(ix&0x7fffffff)) |
return -two25/zero; /* log(+-0)=-inf */ |
if (ix<0) return (x-x)/zero; /* log(-#) = NaN */ |
if (!FLT_UWORD_IS_FINITE(ix)) return x+x; |
if (FLT_UWORD_IS_SUBNORMAL(ix)) { |
k -= 25; x *= two25; /* subnormal number, scale up x */ |
GET_FLOAT_WORD(ix,x); |
} |
k += (ix>>23)-127; |
ix &= 0x007fffff; |
i = (ix+(0x95f64<<3))&0x800000; |
SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */ |
k += (i>>23); |
f = x-(float)1.0; |
if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */ |
if(f==zero) { if(k==0) return zero; else {dk=(float)k; |
return dk*ln2_hi+dk*ln2_lo;}} |
R = f*f*((float)0.5-(float)0.33333333333333333*f); |
if(k==0) return f-R; else {dk=(float)k; |
return dk*ln2_hi-((R-dk*ln2_lo)-f);} |
} |
s = f/((float)2.0+f); |
dk = (float)k; |
z = s*s; |
i = ix-(0x6147a<<3); |
w = z*z; |
j = (0x6b851<<3)-ix; |
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=(float)0.5*f*f; |
if(k==0) return f-(hfsq-s*(hfsq+R)); else |
return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f); |
} else { |
if(k==0) return f-s*(f-R); else |
return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f); |
} |
} |