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 * Return the base 10 logarithm of x. See k_log.c for details on the algorithm.
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,hi,lo,y,z;
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	k += (hx>>23)-127;
50	hx &= 0x007fffff;
51	i = (hx+(0x4afb0d))&0x800000;
52	SET_FLOAT_WORD(x,hx|(i^0x3f800000));	/* normalize x or x/2 */
53	k += (i>>23);
54	y = (float)k;
55	f = __kernel_logf(x);
56	x = x - (float)1.0;
57	GET_FLOAT_WORD(hx,x);
58	SET_FLOAT_WORD(hi,hx&0xfffff000);
59	lo = x - hi;
60	z = y*log10_2lo + (x+f)*ivln10lo + (lo+f)*ivln10hi + hi*ivln10hi;
61	return  z+y*log10_2hi;
62}
63