| /* e_logf.c -- float version of e_log.c. |
| * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. |
| * 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. |
| * ==================================================== |
| */ |
| |
| |
| #include <math.h> |
| #include <math_private.h> |
| |
| static const float |
| ln2 = 0.69314718055994530942, |
| 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 */ |
| |
| static const float zero = 0.0; |
| |
| float |
| __ieee754_log2f(float x) |
| { |
| float hfsq,f,s,z,R,w,t1,t2,dk; |
| int32_t k,ix,i,j; |
| |
| GET_FLOAT_WORD(ix,x); |
| |
| k=0; |
| if (ix < 0x00800000) { /* x < 2**-126 */ |
| if (__builtin_expect((ix&0x7fffffff)==0, 0)) |
| return -two25/(x-x); /* log(+-0)=-inf */ |
| if (__builtin_expect(ix<0, 0)) |
| return (x-x)/(x-x); /* log(-#) = NaN */ |
| k -= 25; x *= two25; /* subnormal number, scale up x */ |
| GET_FLOAT_WORD(ix,x); |
| } |
| if (__builtin_expect(ix >= 0x7f800000, 0)) return x+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); |
| dk = (float)k; |
| f = x-(float)1.0; |
| if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */ |
| if(f==zero) return dk; |
| R = f*f*((float)0.5-(float)0.33333333333333333*f); |
| return dk-(R-f)/ln2; |
| } |
| s = f/((float)2.0+f); |
| 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; |
| return dk-((hfsq-(s*(hfsq+R)))-f)/ln2; |
| } else { |
| return dk-((s*(f-R))-f)/ln2; |
| } |
| } |
| strong_alias (__ieee754_log2f, __log2f_finite) |