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/*
14 * double logb(x)
15 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
16 * Use ilogb instead.
17 */
18
19#include "math.h"
20#include "math_private.h"
21
22double
23logb(double x)
24{
25	int32_t lx,ix;
26	EXTRACT_WORDS(ix,lx,x);
27	ix &= 0x7fffffff;			/* high |x| */
28	if((ix|lx)==0) return -1.0/fabs(x);
29	if(ix>=0x7ff00000) return x*x;
30	if((ix>>=20)==0) 			/* IEEE 754 logb */
31		return -1022.0;
32	else
33		return (double) (ix-1023);
34}
35DEF_STD(logb);
36LDBL_MAYBE_UNUSED_CLONE(logb);
37