1 /* e_logf.c -- float version of e_log.c.
2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
3 * adapted for log2 by Ulrich Drepper <drepper@cygnus.com>
7 * ====================================================
8 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
10 * Developed at SunPro, a Sun Microsystems, Inc. business.
11 * Permission to use, copy, modify, and distribute this
12 * software is freely granted, provided that this notice
14 * ====================================================
19 #include "math_private.h"
26 ln2 = 0.69314718055994530942,
27 two25 = 3.355443200e+07, /* 0x4c000000 */
28 Lg1 = 6.6666668653e-01, /* 3F2AAAAB */
29 Lg2 = 4.0000000596e-01, /* 3ECCCCCD */
30 Lg3 = 2.8571429849e-01, /* 3E924925 */
31 Lg4 = 2.2222198546e-01, /* 3E638E29 */
32 Lg5 = 1.8183572590e-01, /* 3E3A3325 */
33 Lg6 = 1.5313838422e-01, /* 3E1CD04F */
34 Lg7 = 1.4798198640e-01; /* 3E178897 */
37 static const float zero = 0.0;
39 static float zero = 0.0;
43 float __ieee754_log2f(float x)
45 float __ieee754_log2f(x)
49 float hfsq,f,s,z,R,w,t1,t2,dk;
55 if (ix < 0x00800000) { /* x < 2**-126 */
56 if ((ix&0x7fffffff)==0)
57 return -two25/(x-x); /* log(+-0)=-inf */
58 if (ix<0) return (x-x)/(x-x); /* log(-#) = NaN */
59 k -= 25; x *= two25; /* subnormal number, scale up x */
62 if (ix >= 0x7f800000) return x+x;
65 i = (ix+(0x95f64<<3))&0x800000;
66 SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */
70 if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */
71 if(f==zero) return dk;
72 R = f*f*((float)0.5-(float)0.33333333333333333*f);
80 t1= w*(Lg2+w*(Lg4+w*Lg6));
81 t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
86 return dk-((hfsq-(s*(hfsq+R)))-f)/ln2;
88 return dk-((s*(f-R))-f)/ln2;