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 2 logarithm of x. See k_log.c for details on the algorithm.
20 #include "math_private.h"
24 two25 = 3.3554432000e+07, /* 0x4c000000 */
25 ivln2hi = 1.4428710938e+00, /* 0x3fb8b000 */
26 ivln2lo = -1.7605285393e-04; /* 0xb9389ad4 */
28 static const float zero = 0.0;
31 __ieee754_log2f(float x)
39 if (hx < 0x00800000) { /* x < 2**-126 */
40 if ((hx&0x7fffffff)==0)
41 return -two25/zero; /* log(+-0)=-inf */
42 if (hx<0) return (x-x)/zero; /* log(-#) = NaN */
43 k -= 25; x *= two25; /* subnormal number, scale up x */
46 if (hx >= 0x7f800000) return x+x;
49 i = (hx+(0x4afb0d))&0x800000;
50 SET_FLOAT_WORD(x,hx|(i^0x3f800000)); /* normalize x or x/2 */
55 SET_FLOAT_WORD(hi,hx&0xfffff000);
57 return (x+f)*ivln2lo + (lo+f)*ivln2hi + hi*ivln2hi + k;