2 * ====================================================
3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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
9 * ====================================================
12 #include <sys/cdefs.h>
13 __FBSDID("$FreeBSD$");
16 * Return the base 10 logarithm of x. See k_log.c for details on the algorithm.
20 #include "math_private.h"
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 */
30 static const float zero = 0.0;
33 __ieee754_log10f(float x)
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 */
48 if (hx >= 0x7f800000) return x+x;
51 i = (hx+(0x4afb0d))&0x800000;
52 SET_FLOAT_WORD(x,hx|(i^0x3f800000)); /* normalize x or x/2 */
58 SET_FLOAT_WORD(hi,hx&0xfffff000);
60 z = y*log10_2lo + (x+f)*ivln10lo + (lo+f)*ivln10hi + hi*ivln10hi;