e_logf.c revision 8870 
1/* e_logf.c -- float version of e_log.c.
2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
3 */
4
5/*
6 * ====================================================
7 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
8 *
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 * ====================================================
14 */
15
16#ifndef lint
17static char rcsid[] = "$Id: e_logf.c,v 1.1.1.1 1994/08/19 09:39:57 jkh Exp $";
18#endif
19
20#include "math.h"
21#include "math_private.h"
22
23#ifdef __STDC__
24static const float
25#else
26static float
27#endif
28ln2_hi =   6.9313812256e-01,	/* 0x3f317180 */
29ln2_lo =   9.0580006145e-06,	/* 0x3717f7d1 */
30two25 =    3.355443200e+07,	/* 0x4c000000 */
31Lg1 = 6.6666668653e-01,	/* 3F2AAAAB */
32Lg2 = 4.0000000596e-01,	/* 3ECCCCCD */
33Lg3 = 2.8571429849e-01, /* 3E924925 */
34Lg4 = 2.2222198546e-01, /* 3E638E29 */
35Lg5 = 1.8183572590e-01, /* 3E3A3325 */
36Lg6 = 1.5313838422e-01, /* 3E1CD04F */
37Lg7 = 1.4798198640e-01; /* 3E178897 */
38
39#ifdef __STDC__
40static const float zero   =  0.0;
41#else
42static float zero   =  0.0;
43#endif
44
45#ifdef __STDC__
46	float __ieee754_logf(float x)
47#else
48	float __ieee754_logf(x)
49	float x;
50#endif
51{
52	float hfsq,f,s,z,R,w,t1,t2,dk;
53	int32_t k,ix,i,j;
54
55	GET_FLOAT_WORD(ix,x);
56
57	k=0;
58	if (ix < 0x00800000) {			/* x < 2**-126  */
59	    if ((ix&0x7fffffff)==0)
60		return -two25/zero;		/* log(+-0)=-inf */
61	    if (ix<0) return (x-x)/zero;	/* log(-#) = NaN */
62	    k -= 25; x *= two25; /* subnormal number, scale up x */
63	    GET_FLOAT_WORD(ix,x);
64	}
65	if (ix >= 0x7f800000) return x+x;
66	k += (ix>>23)-127;
67	ix &= 0x007fffff;
68	i = (ix+(0x95f64<<3))&0x800000;
69	SET_FLOAT_WORD(x,ix|(i^0x3f800000));	/* normalize x or x/2 */
70	k += (i>>23);
71	f = x-(float)1.0;
72	if((0x007fffff&(15+ix))<16) {	/* |f| < 2**-20 */
73	    if(f==zero) if(k==0) return zero;  else {dk=(float)k;
74				 return dk*ln2_hi+dk*ln2_lo;}
75	    R = f*f*((float)0.5-(float)0.33333333333333333*f);
76	    if(k==0) return f-R; else {dk=(float)k;
77	    	     return dk*ln2_hi-((R-dk*ln2_lo)-f);}
78	}
79 	s = f/((float)2.0+f);
80	dk = (float)k;
81	z = s*s;
82	i = ix-(0x6147a<<3);
83	w = z*z;
84	j = (0x6b851<<3)-ix;
85	t1= w*(Lg2+w*(Lg4+w*Lg6));
86	t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
87	i |= j;
88	R = t2+t1;
89	if(i>0) {
90	    hfsq=(float)0.5*f*f;
91	    if(k==0) return f-(hfsq-s*(hfsq+R)); else
92		     return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f);
93	} else {
94	    if(k==0) return f-s*(f-R); else
95		     return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f);
96	}
97}
98