e_log10f.c revision 226376 
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: head/lib/msun/src/e_log10f.c 226376 2011-10-15 05:23:28Z das $");
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
23static const float
24two25      =  3.3554432000e+07, /* 0x4c000000 */
25ivln10hi   =  4.3432617188e-01, /* 0x3ede6000 */
26ivln10lo   = -3.1689971365e-05, /* 0xb804ead9 */
27log10_2hi  =  3.0102920532e-01, /* 0x3e9a2080 */
28log10_2lo  =  7.9034151668e-07; /* 0x355427db */
29
30static const float zero   =  0.0;
31
32float
33__ieee754_log10f(float x)
34{
35	float f,hfsq,hi,lo,r,y,y2;
36	int32_t i,k,hx;
37
38	GET_FLOAT_WORD(hx,x);
39
40	k=0;
41	if (hx < 0x00800000) {			/* x < 2**-126  */
42	    if ((hx&0x7fffffff)==0)
43		return -two25/zero;		/* log(+-0)=-inf */
44	    if (hx<0) return (x-x)/zero;	/* log(-#) = NaN */
45	    k -= 25; x *= two25; /* subnormal number, scale up x */
46	    GET_FLOAT_WORD(hx,x);
47	}
48	if (hx >= 0x7f800000) return x+x;
49	if (hx == 0x3f800000)
50	    return zero;			/* log(1) = +0 */
51	k += (hx>>23)-127;
52	hx &= 0x007fffff;
53	i = (hx+(0x4afb0d))&0x800000;
54	SET_FLOAT_WORD(x,hx|(i^0x3f800000));	/* normalize x or x/2 */
55	k += (i>>23);
56	y = (float)k;
57	f = x - (float)1.0;
58	hfsq = (float)0.5*f*f;
59	r = k_log1pf(f);
60
61	/* See e_log2f.c and e_log2.c for details. */
62	if (sizeof(float_t) > sizeof(float))
63		return (r - hfsq + f) * ((float_t)ivln10lo + ivln10hi) +
64		    y * ((float_t)log10_2lo + log10_2hi);
65	hi = f - hfsq;
66	GET_FLOAT_WORD(hx,hi);
67	SET_FLOAT_WORD(hi,hx&0xfffff000);
68	lo = (f - hi) - hfsq + r;
69	return y*log10_2lo + (lo+hi)*ivln10lo + lo*ivln10hi + hi*ivln10hi +
70	    y*log10_2hi;
71}
72