1 /*
2 * ====================================================
3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
4 *
5 * Developed at SunPro, a Sun Microsystems, Inc. business.
6 * Permission to use, copy, modify, and distribute this
7 * software is freely granted, provided that this notice
8 * is preserved.
9 * ====================================================
10 */
11
12 #include <sys/cdefs.h>
13 __FBSDID("$FreeBSD$");
14
15 /*
16 * Float version of e_log10.c. See the latter for most comments.
17 */
18
19 #include "math.h"
20 #include "math_private.h"
21 #include "k_logf.h"
22
23 static const float
24 two25 = 3.3554432000e+07, /* 0x4c000000 */
25 ivln10hi = 4.3432617188e-01, /* 0x3ede6000 */
26 ivln10lo = -3.1689971365e-05, /* 0xb804ead9 */
27 log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */
28 log10_2lo = 7.9034151668e-07; /* 0x355427db */
29
30 static const float zero = 0.0;
31 static volatile float vzero = 0.0;
32
33 float
__ieee754_log10f(float x)34 __ieee754_log10f(float x)
35 {
36 float f,hfsq,hi,lo,r,y;
37 int32_t i,k,hx;
38
39 GET_FLOAT_WORD(hx,x);
40
41 k=0;
42 if (hx < 0x00800000) { /* x < 2**-126 */
43 if ((hx&0x7fffffff)==0)
44 return -two25/vzero; /* log(+-0)=-inf */
45 if (hx<0) return (x-x)/zero; /* log(-#) = NaN */
46 k -= 25; x *= two25; /* subnormal number, scale up x */
47 GET_FLOAT_WORD(hx,x);
48 }
49 if (hx >= 0x7f800000) return x+x;
50 if (hx == 0x3f800000)
51 return zero; /* log(1) = +0 */
52 k += (hx>>23)-127;
53 hx &= 0x007fffff;
54 i = (hx+(0x4afb0d))&0x800000;
55 SET_FLOAT_WORD(x,hx|(i^0x3f800000)); /* normalize x or x/2 */
56 k += (i>>23);
57 y = (float)k;
58 f = x - (float)1.0;
59 hfsq = (float)0.5*f*f;
60 r = k_log1pf(f);
61
62 /* See e_log2f.c and e_log2.c for details. */
63 if (sizeof(float_t) > sizeof(float))
64 return (r - hfsq + f) * ((float_t)ivln10lo + ivln10hi) +
65 y * ((float_t)log10_2lo + log10_2hi);
66 hi = f - hfsq;
67 GET_FLOAT_WORD(hx,hi);
68 SET_FLOAT_WORD(hi,hx&0xfffff000);
69 lo = (f - hi) - hfsq + r;
70 return y*log10_2lo + (lo+hi)*ivln10lo + lo*ivln10hi + hi*ivln10hi +
71 y*log10_2hi;
72 }
73