1/* @(#)s_ilogb.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_ilogb.c,v 1.16 2016/08/26 08:20:31 christos Exp $");
16#endif
17
18/* ilogb(double x)
19 * return the binary exponent of non-zero x
20 * ilogb(0) = 0x80000001
21 * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
22 */
23
24#include <math.h>
25#define __TEST_FENV
26#include <fenv.h>
27#ifndef __HAVE_FENV
28#define feraiseexcept(a)
29#endif
30#include "math_private.h"
31
32#ifndef __HAVE_LONG_DOUBLE
33__strong_alias(ilogbl,ilogb)
34#endif
35
36int
37ilogb(double x)
38{
39	int32_t hx, lx, ix;
40
41	GET_HIGH_WORD(hx, x);
42	hx &= 0x7fffffff;
43	if (hx < 0x00100000) {
44		GET_LOW_WORD(lx, x);
45		if ((hx | lx) == 0) {
46			feraiseexcept(FE_INVALID);
47			return FP_ILOGB0;	/* ilogb(0) = 0x80000001 */
48		}
49		if (hx == 0) {
50			for (ix = -1043; lx > 0; lx <<= 1) ix -= 1;
51		} else {
52			for (ix = -1022, hx <<= 11; hx > 0; hx <<= 1) ix -= 1;
53		}
54		return ix;
55	}
56
57	if (hx < 0x7ff00000) {
58		return (hx >> 20) - 1023;
59	}
60
61	feraiseexcept(FE_INVALID);
62	return isnan(x) ? FP_ILOGBNAN : INT_MAX;
63}
64