e_logf.c revision 97409 
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[] = "$FreeBSD: head/lib/msun/src/e_logf.c 97409 2002-05-28 17:51:46Z alfred $";
18#endif
19
20#include "math.h"
21#include "math_private.h"
22
23static const float
24ln2_hi =   6.9313812256e-01,	/* 0x3f317180 */
25ln2_lo =   9.0580006145e-06,	/* 0x3717f7d1 */
26two25 =    3.355443200e+07,	/* 0x4c000000 */
27Lg1 = 6.6666668653e-01,	/* 3F2AAAAB */
28Lg2 = 4.0000000596e-01,	/* 3ECCCCCD */
29Lg3 = 2.8571429849e-01, /* 3E924925 */
30Lg4 = 2.2222198546e-01, /* 3E638E29 */
31Lg5 = 1.8183572590e-01, /* 3E3A3325 */
32Lg6 = 1.5313838422e-01, /* 3E1CD04F */
33Lg7 = 1.4798198640e-01; /* 3E178897 */
34
35static const float zero   =  0.0;
36
37	float __ieee754_logf(float x)
38{
39	float hfsq,f,s,z,R,w,t1,t2,dk;
40	int32_t k,ix,i,j;
41
42	GET_FLOAT_WORD(ix,x);
43
44	k=0;
45	if (ix < 0x00800000) {			/* x < 2**-126  */
46	    if ((ix&0x7fffffff)==0)
47		return -two25/zero;		/* log(+-0)=-inf */
48	    if (ix<0) return (x-x)/zero;	/* log(-#) = NaN */
49	    k -= 25; x *= two25; /* subnormal number, scale up x */
50	    GET_FLOAT_WORD(ix,x);
51	}
52	if (ix >= 0x7f800000) 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	f = x-(float)1.0;
59	if((0x007fffff&(15+ix))<16) {	/* |f| < 2**-20 */
60	    if(f==zero) if(k==0) return zero;  else {dk=(float)k;
61				 return dk*ln2_hi+dk*ln2_lo;}
62	    R = f*f*((float)0.5-(float)0.33333333333333333*f);
63	    if(k==0) return f-R; else {dk=(float)k;
64	    	     return dk*ln2_hi-((R-dk*ln2_lo)-f);}
65	}
66 	s = f/((float)2.0+f);
67	dk = (float)k;
68	z = s*s;
69	i = ix-(0x6147a<<3);
70	w = z*z;
71	j = (0x6b851<<3)-ix;
72	t1= w*(Lg2+w*(Lg4+w*Lg6));
73	t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
74	i |= j;
75	R = t2+t1;
76	if(i>0) {
77	    hfsq=(float)0.5*f*f;
78	    if(k==0) return f-(hfsq-s*(hfsq+R)); else
79		     return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f);
80	} else {
81	    if(k==0) return f-s*(f-R); else
82		     return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f);
83	}
84}
85