Annotation of src/lib/libm/src/e_logf.c, Revision 1.8
1.1 jtc 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
1.7 simonb 11: * software is freely granted, provided that this notice
1.1 jtc 12: * is preserved.
13: * ====================================================
14: */
15:
1.5 lukem 16: #include <sys/cdefs.h>
1.3 jtc 17: #if defined(LIBM_SCCS) && !defined(lint)
1.8 ! wiz 18: __RCSID("$NetBSD: e_logf.c,v 1.7 1999/07/02 15:37:40 simonb Exp $");
1.1 jtc 19: #endif
20:
21: #include "math.h"
22: #include "math_private.h"
23:
24: static const float
25: ln2_hi = 6.9313812256e-01, /* 0x3f317180 */
26: ln2_lo = 9.0580006145e-06, /* 0x3717f7d1 */
27: two25 = 3.355443200e+07, /* 0x4c000000 */
28: Lg1 = 6.6666668653e-01, /* 3F2AAAAB */
29: Lg2 = 4.0000000596e-01, /* 3ECCCCCD */
30: Lg3 = 2.8571429849e-01, /* 3E924925 */
31: Lg4 = 2.2222198546e-01, /* 3E638E29 */
32: Lg5 = 1.8183572590e-01, /* 3E3A3325 */
33: Lg6 = 1.5313838422e-01, /* 3E1CD04F */
34: Lg7 = 1.4798198640e-01; /* 3E178897 */
35:
36: static const float zero = 0.0;
37:
1.8 ! wiz 38: float
! 39: __ieee754_logf(float x)
1.1 jtc 40: {
41: float hfsq,f,s,z,R,w,t1,t2,dk;
1.2 jtc 42: int32_t k,ix,i,j;
1.1 jtc 43:
44: GET_FLOAT_WORD(ix,x);
45:
46: k=0;
47: if (ix < 0x00800000) { /* x < 2**-126 */
1.7 simonb 48: if ((ix&0x7fffffff)==0)
1.1 jtc 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);
1.7 simonb 53: }
1.1 jtc 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 */
1.6 thorpej 62: if(f==zero) { if(k==0) return zero; else {dk=(float)k;
63: return dk*ln2_hi+dk*ln2_lo;}
64: }
1.1 jtc 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: }
1.7 simonb 69: s = f/((float)2.0+f);
1.1 jtc 70: dk = (float)k;
71: z = s*s;
72: i = ix-(0x6147a<<3);
73: w = z*z;
74: j = (0x6b851<<3)-ix;
1.7 simonb 75: t1= w*(Lg2+w*(Lg4+w*Lg6));
76: t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
1.1 jtc 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: }
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