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1/* e_log10f.c -- float version of e_log10.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 "math.h"
17#include "math_private.h"
18
19static const float
20two25 = 3.3554432000e+07, /* 0x4c000000 */
21ivln10 = 4.3429449201e-01, /* 0x3ede5bd9 */
22log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */
23log10_2lo = 7.9034151668e-07; /* 0x355427db */
24
25static const float zero = 0.0;
26
27float
28log10f(float x)
29{
30 float y,z;
31 int32_t i,k,hx;
32
33 GET_FLOAT_WORD(hx,x);
34
35 k=0;
36 if (hx < 0x00800000) { /* x < 2**-126 */
37 if ((hx&0x7fffffff)==0)
38 return -two25/zero; /* log(+-0)=-inf */
39 if (hx<0) return (x-x)/zero; /* log(-#) = NaN */
40 k -= 25; x *= two25; /* subnormal number, scale up x */
41 GET_FLOAT_WORD(hx,x);
42 }
43 if (hx >= 0x7f800000) return x+x;
44 k += (hx>>23)-127;
45 i = ((u_int32_t)k&0x80000000)>>31;
46 hx = (hx&0x007fffff)|((0x7f-i)<<23);
47 y = (float)(k+i);
48 SET_FLOAT_WORD(x,hx);
49 z = y*log10_2lo + ivln10*logf(x);
50 return z+y*log10_2hi;
51}