2 /* @(#)e_log10.c 1.3 95/01/18 */
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
7 * Developed at SunSoft, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
11 * ====================================================
14 #include <sys/cdefs.h>
15 __FBSDID("$FreeBSD$");
18 * Return the base 10 logarithm of x. See k_log.c for details on the algorithm.
22 #include "math_private.h"
26 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
27 ivln10hi = 4.34294481878168880939e-01, /* 0x3fdbcb7b, 0x15200000 */
28 ivln10lo = 2.50829467116452752298e-11, /* 0x3dbb9438, 0xca9aadd5 */
29 log10_2hi = 3.01029995663611771306e-01, /* 0x3FD34413, 0x509F6000 */
30 log10_2lo = 3.69423907715893078616e-13; /* 0x3D59FEF3, 0x11F12B36 */
32 static const double zero = 0.0;
35 __ieee754_log10(double x)
41 EXTRACT_WORDS(hx,lx,x);
44 if (hx < 0x00100000) { /* x < 2**-1022 */
45 if (((hx&0x7fffffff)|lx)==0)
46 return -two54/zero; /* log(+-0)=-inf */
47 if (hx<0) return (x-x)/zero; /* log(-#) = NaN */
48 k -= 54; x *= two54; /* subnormal number, scale up x */
51 if (hx >= 0x7ff00000) return x+x;
54 i = (hx+0x95f64)&0x100000;
55 SET_HIGH_WORD(x,hx|(i^0x3ff00000)); /* normalize x or x/2 */
62 z = y*log10_2lo + (x+f)*ivln10lo + (lo+f)*ivln10hi + hi*ivln10hi;