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[dragonfly.git] / lib / libm / src / e_log2f.c
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1 /* e_logf.c -- float version of e_log.c.
2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
3 */
5 /*
6 * ====================================================
7 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
9 * Developed at SunPro, a Sun Microsystems, Inc. business.
10 * Permission to use, copy, modify, and distribute this
11 * software is freely granted, provided that this notice
12 * is preserved.
13 * ====================================================
15 * $NetBSD: e_log2f.c,v 1.1 2005/07/21 12:55:58 christos Exp $
16 * $DragonFly: src/lib/libm/src/e_log2f.c,v 1.1 2007/06/16 22:26:53 pavalos Exp $
19 #include <math.h>
20 #include "math_private.h"
22 static const float
23 ln2 = 0.6931471805599452862268,
24 two25 = 3.355443200e+07, /* 0x4c000000 */
25 Lg1 = 6.6666668653e-01, /* 3F2AAAAB */
26 Lg2 = 4.0000000596e-01, /* 3ECCCCCD */
27 Lg3 = 2.8571429849e-01, /* 3E924925 */
28 Lg4 = 2.2222198546e-01, /* 3E638E29 */
29 Lg5 = 1.8183572590e-01, /* 3E3A3325 */
30 Lg6 = 1.5313838422e-01, /* 3E1CD04F */
31 Lg7 = 1.4798198640e-01; /* 3E178897 */
33 static const float zero = 0.0;
35 float
36 log2f(float x)
38 float hfsq,f,s,z,R,w,t1,t2,dk;
39 int32_t k,ix,i,j;
41 GET_FLOAT_WORD(ix,x);
43 k=0;
44 if (ix < 0x00800000) { /* x < 2**-126 */
45 if ((ix&0x7fffffff)==0)
46 return -two25/zero; /* log(+-0)=-inf */
47 if (ix<0) return (x-x)/zero; /* log(-#) = NaN */
48 k -= 25; x *= two25; /* subnormal number, scale up x */
49 GET_FLOAT_WORD(ix,x);
51 if (ix >= 0x7f800000) return x+x;
52 k += (ix>>23)-127;
53 ix &= 0x007fffff;
54 i = (ix+(0x95f64<<3))&0x800000;
55 SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */
56 k += (i>>23);
57 dk = (float)k;
58 f = x-(float)1.0;
59 if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */
60 if (f==zero)
61 return (dk);
62 R = f*f*((float)0.5-(float)0.33333333333333333*f);
63 return (dk-(R-f)/ln2);
65 s = f/((float)2.0+f);
66 z = s*s;
67 i = ix-(0x6147a<<3);
68 w = z*z;
69 j = (0x6b851<<3)-ix;
70 t1= w*(Lg2+w*(Lg4+w*Lg6));
71 t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
72 i |= j;
73 R = t2+t1;
74 if(i>0) {
75 hfsq=(float)0.5*f*f;
76 return (dk-(hfsq-s*(hfsq+R)-f)/ln2);
77 } else
78 return (dk-((s*(f-R))-f)/ln2);