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>
4 */
5
6/*
7 * ====================================================
8 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
9 *
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
13 * is preserved.
14 * ====================================================
15 */
16
17
18#include <math.h>
19#include <math_private.h>
20#include <fix-int-fp-convert-zero.h>
21
22static const float
23ln2 = 0.69314718055994530942,
24two25 = 3.355443200e+07, /* 0x4c000000 */
25Lg1 = 6.6666668653e-01, /* 3F2AAAAB */
26Lg2 = 4.0000000596e-01, /* 3ECCCCCD */
27Lg3 = 2.8571429849e-01, /* 3E924925 */
28Lg4 = 2.2222198546e-01, /* 3E638E29 */
29Lg5 = 1.8183572590e-01, /* 3E3A3325 */
30Lg6 = 1.5313838422e-01, /* 3E1CD04F */
31Lg7 = 1.4798198640e-01; /* 3E178897 */
32
33static const float zero = 0.0;
34
35float
36__ieee754_log2f(float x)
37{
38 float hfsq,f,s,z,R,w,t1,t2,dk;
39 int32_t k,ix,i,j;
40
41 GET_FLOAT_WORD(ix,x);
42
43 k=0;
44 if (ix < 0x00800000) { /* x < 2**-126 */
45 if (__builtin_expect((ix&0x7fffffff)==0, 0))
46 return -two25/__fabsf (x); /* log(+-0)=-inf */
47 if (__builtin_expect(ix<0, 0))
48 return (x-x)/(x-x); /* log(-#) = NaN */
49 k -= 25; x *= two25; /* subnormal number, scale up x */
50 GET_FLOAT_WORD(ix,x);
51 }
52 if (__builtin_expect(ix >= 0x7f800000, 0)) return x+x;
53 k += (ix>>23)-127;
54 ix &= 0x007fffff;
55 i = (ix+(0x95f64<<3))&0x800000;
56 SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */
57 k += (i>>23);
58 dk = (float)k;
59 f = x-(float)1.0;
60 if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */
61 if(f==zero)
62 {
63 if (FIX_INT_FP_CONVERT_ZERO && dk == 0.0f)
64 dk = 0.0f;
65 return dk;
66 }
67 R = f*f*((float)0.5-(float)0.33333333333333333*f);
68 return dk-(R-f)/ln2;
69 }
70 s = f/((float)2.0+f);
71 z = s*s;
72 i = ix-(0x6147a<<3);
73 w = z*z;
74 j = (0x6b851<<3)-ix;
75 t1= w*(Lg2+w*(Lg4+w*Lg6));
76 t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
77 i |= j;
78 R = t2+t1;
79 if(i>0) {
80 hfsq=(float)0.5*f*f;
81 return dk-((hfsq-(s*(hfsq+R)))-f)/ln2;
82 } else {
83 return dk-((s*(f-R))-f)/ln2;
84 }
85}
86strong_alias (__ieee754_log2f, __log2f_finite)
87