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) |
14 | static 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 | |
28 | int |
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 | |