e_log2f.c revision 97413 
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#ifndef lint
17static char rcsid[] = "$FreeBSD: head/lib/msun/src/e_log10f.c 97413 2002-05-28 18:15:04Z alfred $";
18#endif
19
20#include "math.h"
21#include "math_private.h"
22
23static const float
24two25      =  3.3554432000e+07, /* 0x4c000000 */
25ivln10     =  4.3429449201e-01, /* 0x3ede5bd9 */
26log10_2hi  =  3.0102920532e-01, /* 0x3e9a2080 */
27log10_2lo  =  7.9034151668e-07; /* 0x355427db */
28
29static const float zero   =  0.0;
30
31float
32__ieee754_log10f(float x)
33{
34	float y,z;
35	int32_t i,k,hx;
36
37	GET_FLOAT_WORD(hx,x);
38
39        k=0;
40        if (hx < 0x00800000) {                  /* x < 2**-126  */
41            if ((hx&0x7fffffff)==0)
42                return -two25/zero;             /* log(+-0)=-inf */
43            if (hx<0) return (x-x)/zero;        /* log(-#) = NaN */
44            k -= 25; x *= two25; /* subnormal number, scale up x */
45	    GET_FLOAT_WORD(hx,x);
46        }
47	if (hx >= 0x7f800000) return x+x;
48	k += (hx>>23)-127;
49	i  = ((u_int32_t)k&0x80000000)>>31;
50        hx = (hx&0x007fffff)|((0x7f-i)<<23);
51        y  = (float)(k+i);
52	SET_FLOAT_WORD(x,hx);
53	z  = y*log10_2lo + ivln10*__ieee754_logf(x);
54	return  z+y*log10_2hi;
55}
56