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 #if defined(LIBM_SCCS) && !defined(lint)
15 __RCSID("$NetBSD: s_logb.c,v 1.12 2011/08/03 14:13:07 joerg Exp $");
16 #endif
17
18 /*
19 * double logb(x)
20 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
21 * Use ilogb instead.
22 */
23
24 #include "math.h"
25 #include "math_private.h"
26
27 #ifndef __HAVE_LONG_DOUBLE
__strong_alias(logbl,logb)28 __strong_alias(logbl,logb)
29 #endif
30
31 double
32 logb(double x)
33 {
34 int32_t lx,ix;
35 EXTRACT_WORDS(ix,lx,x);
36 ix &= 0x7fffffff; /* high |x| */
37 if((ix|lx)==0) return -1.0/fabs(x);
38 if(ix>=0x7ff00000) return x*x;
39 if((ix>>=20)==0) /* IEEE 754 logb */
40 return -1022.0;
41 else
42 return (double) (ix-1023);
43 }
44