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#if defined(LIBM_SCCS) && !defined(lint)
14static char rcsid[] = "$NetBSD: s_ilogb.c,v 1.9 1995/05/10 20:47:28 jtc Exp $";
15#endif
16
17/* ilogb(double x)
18 * return the binary exponent of non-zero x
19 * ilogb(0) = FP_ILOGB0
20 * ilogb(NaN) = FP_ILOGBNAN (no signal is raised)
21 * ilogb(+-Inf) = INT_MAX (no signal is raised)
22 */
23
24#include <limits.h>
25#include <math.h>
26#include <math_private.h>
27
28int
29__ieee754_ilogb (double x)
30{
31 int32_t hx, lx, ix;
32
33 GET_HIGH_WORD (hx, x);
34 hx &= 0x7fffffff;
35 if (hx < 0x00100000)
36 {
37 GET_LOW_WORD (lx, x);
38 if ((hx | lx) == 0)
39 return FP_ILOGB0; /* ilogb(0) = FP_ILOGB0 */
40 else /* subnormal x */
41 if (hx == 0)
42 {
43 for (ix = -1043; lx > 0; lx <<= 1)
44 ix -= 1;
45 }
46 else
47 {
48 for (ix = -1022, hx <<= 11; hx > 0; hx <<= 1)
49 ix -= 1;
50 }
51 return ix;
52 }
53 else if (hx < 0x7ff00000)
54 return (hx >> 20) - 1023;
55 else if (FP_ILOGBNAN != INT_MAX)
56 {
57 /* ISO C99 requires ilogb(+-Inf) == INT_MAX. */
58 GET_LOW_WORD (lx, x);
59 if (((hx ^ 0x7ff00000) | lx) == 0)
60 return INT_MAX;
61 }
62 return FP_ILOGBNAN;
63}
64