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
__strong_alias(ilogbl,ilogb)33 __strong_alias(ilogbl,ilogb)
34 #endif
35
36 int
37 ilogb(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