s_logb.c revision 2116 
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#ifndef lint
14static char rcsid[] = "$Id: s_logb.c,v 1.6 1994/08/18 23:07:04 jtc Exp $";
15#endif
16
17/*
18 * double logb(x)
19 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
20 * Use ilogb instead.
21 */
22
23#include "math.h"
24#include "math_private.h"
25
26#ifdef __STDC__
27	double logb(double x)
28#else
29	double logb(x)
30	double x;
31#endif
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>>=20)==0) 			/* IEEE 754 logb */
39		return -1022.0;
40	else
41		return (double) (ix-1023);
42}
43