1
2 /* @(#)s_ilogb.c 5.1 93/09/24 */
3 /*
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 *
7 * Developed at SunPro, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
10 * is preserved.
11 * ====================================================
12 */
13
14 /*
15 FUNCTION
16 <<ilogb>>, <<ilogbf>>---get exponent of floating-point number
17 INDEX
18 ilogb
19 INDEX
20 ilogbf
21
22 SYNOPSIS
23 #include <math.h>
24 int ilogb(double <[val]>);
25 int ilogbf(float <[val]>);
26
27 DESCRIPTION
28
29 All nonzero, normal numbers can be described as <[m]> *
30 2**<[p]>. <<ilogb>> and <<ilogbf>> examine the argument
31 <[val]>, and return <[p]>. The functions <<frexp>> and
32 <<frexpf>> are similar to <<ilogb>> and <<ilogbf>>, but also
33 return <[m]>.
34
35 RETURNS
36
37 <<ilogb>> and <<ilogbf>> return the power of two used to form the
38 floating-point argument.
39 If <[val]> is <<0>>, they return <<FP_ILOGB0>>.
40 If <[val]> is infinite, they return <<INT_MAX>>.
41 If <[val]> is NaN, they return <<FP_ILOGBNAN>>.
42 (<<FP_ILOGB0>> and <<FP_ILOGBNAN>> are defined in math.h, but in turn are
43 defined as INT_MIN or INT_MAX from limits.h. The value of FP_ILOGB0 may be
44 either INT_MIN or -INT_MAX. The value of FP_ILOGBNAN may be either INT_MAX or
45 INT_MIN.)
46
47 @comment The bugs might not be worth noting, given the mass non-C99/POSIX
48 @comment behavior of much of the Newlib math library.
49 @comment BUGS
50 @comment On errors, errno is not set per C99 and POSIX requirements even if
51 @comment (math_errhandling & MATH_ERRNO) is non-zero.
52
53 PORTABILITY
54 C99, POSIX
55 */
56
57 /* ilogb(double x)
58 * return the binary exponent of non-zero x
59 * ilogb(0) = 0x80000001
60 * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
61 */
62
63 #include <limits.h>
64 #include "fdlibm.h"
65
66 #ifdef _NEED_FLOAT64
67
68 int
ilogb64(__float64 x)69 ilogb64(__float64 x)
70 {
71 __int32_t hx,lx,ix;
72
73 EXTRACT_WORDS(hx,lx,x);
74 hx &= 0x7fffffff;
75 if(hx<0x00100000) {
76 if((hx|lx)==0) {
77 (void) __math_invalid(_F_64(0.0));
78 return FP_ILOGB0; /* ilogb(0) = special case error */
79 } else /* subnormal x */
80 if(hx==0) {
81 for (ix = -1043; lx>0; lx<<=1) ix -=1;
82 } else {
83 for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
84 }
85 return ix;
86 }
87 else if (hx<0x7ff00000) return (hx>>20)-1023;
88 #if FP_ILOGBNAN != INT_MAX
89 else if (hx>0x7ff00000) {
90 (void) __math_invalid(_F_64(0.0));
91 return FP_ILOGBNAN; /* NAN */
92 }
93 #endif
94 else {
95 (void) __math_invalid(_F_64(0.0));
96 return INT_MAX; /* infinite (or, possibly, NAN) */
97 }
98 }
99
100 _MATH_ALIAS_i_d(ilogb)
101
102 #endif /* _NEED_FLOAT64 */
103
