1/* @(#)s_logb.c 5.1 93/09/24 */
2/*
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5 *
6 * Developed at SunPro, a Sun Microsystems, Inc. business.
7 * Permission to use, copy, modify, and distribute this
8 * software is freely granted, provided that this notice
9 * is preserved.
10 * ====================================================
11 */
12
13#include <sys/cdefs.h>
14__FBSDID("$FreeBSD$");
15
16/*
17 * double logb(x)
18 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
19 * Use ilogb instead.
20 */
21
22#include <float.h>
23
24#include "math.h"
25#include "math_private.h"
26
27static const double
28two54 = 1.80143985094819840000e+16;	/* 43500000 00000000 */
29
30double
31logb(double x)
32{
33	int32_t lx,ix;
34	EXTRACT_WORDS(ix,lx,x);
35	ix &= 0x7fffffff;			/* high |x| */
36	if((ix|lx)==0) return -1.0/fabs(x);
37	if(ix>=0x7ff00000) return x*x;
38	if(ix<0x00100000) {
39		x *= two54;		 /* convert subnormal x to normal */
40		GET_HIGH_WORD(ix,x);
41		ix &= 0x7fffffff;
42		return (double) ((ix>>20)-1023-54);
43	} else
44		return (double) ((ix>>20)-1023);
45}
46
47#if (LDBL_MANT_DIG == 53)
48__weak_reference(logb, logbl);
49#endif
50