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e_logf.c (2442B)
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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 */
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
17 static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_logf.c,v 1.7 2002/05/28 18:15:04 alfred Exp $";
18 #endif
19
20 #include "math.h"
21 #include "math_private.h"
22
23 static const float
24 ln2_hi = 6.9313812256e-01, /* 0x3f317180 */
25 ln2_lo = 9.0580006145e-06, /* 0x3717f7d1 */
26 two25 = 3.355443200e+07, /* 0x4c000000 */
27 Lg1 = 6.6666668653e-01, /* 3F2AAAAB */
28 Lg2 = 4.0000000596e-01, /* 3ECCCCCD */
29 Lg3 = 2.8571429849e-01, /* 3E924925 */
30 Lg4 = 2.2222198546e-01, /* 3E638E29 */
31 Lg5 = 1.8183572590e-01, /* 3E3A3325 */
32 Lg6 = 1.5313838422e-01, /* 3E1CD04F */
33 Lg7 = 1.4798198640e-01; /* 3E178897 */
34
35 static const float zero = 0.0;
36
37 float
38 __ieee754_logf(float x)
39 {
40 float hfsq,f,s,z,R,w,t1,t2,dk;
41 int32_t k,ix,i,j;
42
43 GET_FLOAT_WORD(ix,x);
44
45 k=0;
46 if (ix < 0x00800000) { /* x < 2**-126 */
47 if ((ix&0x7fffffff)==0)
48 return -two25/zero; /* log(+-0)=-inf */
49 if (ix<0) return (x-x)/zero; /* log(-#) = NaN */
50 k -= 25; x *= two25; /* subnormal number, scale up x */
51 GET_FLOAT_WORD(ix,x);
52 }
53 if (ix >= 0x7f800000) return x+x;
54 k += (ix>>23)-127;
55 ix &= 0x007fffff;
56 i = (ix+(0x95f64<<3))&0x800000;
57 SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */
58 k += (i>>23);
59 f = x-(float)1.0;
60 if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */
61 if(f==zero) if(k==0) return zero; else {dk=(float)k;
62 return dk*ln2_hi+dk*ln2_lo;}
63 R = f*f*((float)0.5-(float)0.33333333333333333*f);
64 if(k==0) return f-R; else {dk=(float)k;
65 return dk*ln2_hi-((R-dk*ln2_lo)-f);}
66 }
67 s = f/((float)2.0+f);
68 dk = (float)k;
69 z = s*s;
70 i = ix-(0x6147a<<3);
71 w = z*z;
72 j = (0x6b851<<3)-ix;
73 t1= w*(Lg2+w*(Lg4+w*Lg6));
74 t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
75 i |= j;
76 R = t2+t1;
77 if(i>0) {
78 hfsq=(float)0.5*f*f;
79 if(k==0) return f-(hfsq-s*(hfsq+R)); else
80 return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f);
81 } else {
82 if(k==0) return f-s*(f-R); else
83 return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f);
84 }
85 }