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#include <sys/cdefs.h>
17#if defined(LIBM_SCCS) && !defined(lint)
18__RCSID("$NetBSD: e_logf.c,v 1.7 1999/07/02 15:37:40 simonb Exp $");
19#endif
20
21#include "math.h"
22#include "math_private.h"
23
24static const float
25ln2_hi =   6.9313812256e-01,	/* 0x3f317180 */
26ln2_lo =   9.0580006145e-06,	/* 0x3717f7d1 */
27two25 =    3.355443200e+07,	/* 0x4c000000 */
28Lg1 = 6.6666668653e-01,	/* 3F2AAAAB */
29Lg2 = 4.0000000596e-01,	/* 3ECCCCCD */
30Lg3 = 2.8571429849e-01, /* 3E924925 */
31Lg4 = 2.2222198546e-01, /* 3E638E29 */
32Lg5 = 1.8183572590e-01, /* 3E3A3325 */
33Lg6 = 1.5313838422e-01, /* 3E1CD04F */
34Lg7 = 1.4798198640e-01; /* 3E178897 */
35
36static const float zero   =  0.0;
37
38float
39__ieee754_logf(float x)
40{
41	float hfsq,f,s,z,R,w,t1,t2,dk;
42	int32_t k,ix,i,j;
43
44	GET_FLOAT_WORD(ix,x);
45
46	k=0;
47	if (ix < 0x00800000) {			/* x < 2**-126  */
48	    if ((ix&0x7fffffff)==0)
49		return -two25/zero;		/* log(+-0)=-inf */
50	    if (ix<0) return (x-x)/zero;	/* log(-#) = NaN */
51	    k -= 25; x *= two25; /* subnormal number, scale up x */
52	    GET_FLOAT_WORD(ix,x);
53	}
54	if (ix >= 0x7f800000) return x+x;
55	k += (ix>>23)-127;
56	ix &= 0x007fffff;
57	i = (ix+(0x95f64<<3))&0x800000;
58	SET_FLOAT_WORD(x,ix|(i^0x3f800000));	/* normalize x or x/2 */
59	k += (i>>23);
60	f = x-(float)1.0;
61	if((0x007fffff&(15+ix))<16) {	/* |f| < 2**-20 */
62	    if(f==zero) { if(k==0) return zero;  else {dk=(float)k;
63				   return dk*ln2_hi+dk*ln2_lo;}
64	    }
65	    R = f*f*((float)0.5-(float)0.33333333333333333*f);
66	    if(k==0) return f-R; else {dk=(float)k;
67	    	     return dk*ln2_hi-((R-dk*ln2_lo)-f);}
68	}
69 	s = f/((float)2.0+f);
70	dk = (float)k;
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	    if(k==0) return f-(hfsq-s*(hfsq+R)); else
82		     return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f);
83	} else {
84	    if(k==0) return f-s*(f-R); else
85		     return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f);
86	}
87}
88