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595e113b | 1 | /* count-trailing-zeros.h -- counts the number of trailing 0 bits in a word. |
ba318903 | 2 | Copyright 2013-2014 Free Software Foundation, Inc. |
595e113b PE |
3 | |
4 | This program is free software: you can redistribute it and/or modify | |
5 | it under the terms of the GNU General Public License as published by | |
6 | the Free Software Foundation; either version 3 of the License, or | |
7 | (at your option) any later version. | |
8 | ||
9 | This program is distributed in the hope that it will be useful, | |
10 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
12 | GNU General Public License for more details. | |
13 | ||
14 | You should have received a copy of the GNU General Public License | |
15 | along with this program. If not, see <http://www.gnu.org/licenses/>. */ | |
16 | ||
17 | /* Written by Paul Eggert. */ | |
18 | ||
19 | #ifndef COUNT_TRAILING_ZEROS_H | |
20 | #define COUNT_TRAILING_ZEROS_H 1 | |
21 | ||
22 | #include <limits.h> | |
23 | #include <stdlib.h> | |
24 | ||
25 | #ifndef _GL_INLINE_HEADER_BEGIN | |
26 | #error "Please include config.h first." | |
27 | #endif | |
28 | _GL_INLINE_HEADER_BEGIN | |
29 | #ifndef COUNT_TRAILING_ZEROS_INLINE | |
30 | # define COUNT_TRAILING_ZEROS_INLINE _GL_INLINE | |
31 | #endif | |
32 | ||
33 | /* Assuming the GCC builtin is BUILTIN and the MSC builtin is MSC_BUILTIN, | |
34 | expand to code that computes the number of trailing zeros of the local | |
35 | variable 'x' of type TYPE (an unsigned integer type) and return it | |
36 | from the current function. */ | |
37 | #if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) | |
38 | # define COUNT_TRAILING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \ | |
39 | return x ? BUILTIN (x) : CHAR_BIT * sizeof x; | |
40 | #elif _MSC_VER | |
41 | # pragma intrinsic _BitScanForward | |
42 | # pragma intrinsic _BitScanForward64 | |
43 | # define COUNT_TRAILING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \ | |
44 | do \ | |
45 | { \ | |
46 | unsigned long result; \ | |
47 | return MSC_BUILTIN (&result, x) ? result : CHAR_BIT * sizeof x; \ | |
48 | } \ | |
49 | while (0) | |
50 | #else | |
51 | # define COUNT_TRAILING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \ | |
52 | do \ | |
53 | { \ | |
54 | int count = 0; \ | |
55 | if (! x) \ | |
56 | return CHAR_BIT * sizeof x; \ | |
57 | for (count = 0; \ | |
58 | (count < CHAR_BIT * sizeof x - 32 \ | |
59 | && ! (x & 0xffffffffU)); \ | |
60 | count += 32) \ | |
61 | x = x >> 31 >> 1; \ | |
62 | return count + count_trailing_zeros_32 (x); \ | |
63 | } \ | |
64 | while (0) | |
65 | ||
66 | /* Compute and return the number of trailing zeros in the least | |
67 | significant 32 bits of X. One of these bits must be nonzero. */ | |
68 | COUNT_TRAILING_ZEROS_INLINE int | |
69 | count_trailing_zeros_32 (unsigned int x) | |
70 | { | |
71 | /* http://graphics.stanford.edu/~seander/bithacks.html */ | |
72 | static const char de_Bruijn_lookup[32] = { | |
73 | 0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8, | |
74 | 31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9 | |
75 | }; | |
76 | return de_Bruijn_lookup[(((x & -x) * 0x077cb531U) & 0xffffffffU) >> 27]; | |
77 | } | |
78 | #endif | |
79 | ||
80 | /* Compute and return the number of trailing zeros in X. */ | |
81 | COUNT_TRAILING_ZEROS_INLINE int | |
82 | count_trailing_zeros (unsigned int x) | |
83 | { | |
84 | COUNT_TRAILING_ZEROS (__builtin_ctz, _BitScanForward, unsigned int); | |
85 | } | |
86 | ||
87 | /* Compute and return the number of trailing zeros in X. */ | |
88 | COUNT_TRAILING_ZEROS_INLINE int | |
89 | count_trailing_zeros_l (unsigned long int x) | |
90 | { | |
91 | COUNT_TRAILING_ZEROS (__builtin_ctzl, _BitScanForward, unsigned long int); | |
92 | } | |
93 | ||
94 | #if HAVE_UNSIGNED_LONG_LONG_INT | |
95 | /* Compute and return the number of trailing zeros in X. */ | |
96 | COUNT_TRAILING_ZEROS_INLINE int | |
97 | count_trailing_zeros_ll (unsigned long long int x) | |
98 | { | |
99 | COUNT_TRAILING_ZEROS (__builtin_ctzll, _BitScanForward64, | |
100 | unsigned long long int); | |
101 | } | |
102 | #endif | |
103 | ||
104 | _GL_INLINE_HEADER_END | |
105 | ||
106 | #endif |