| 1 | /* count-trailing-zeros.h -- counts the number of trailing 0 bits in a word. |
| 2 | Copyright 2013-2014 Free Software Foundation, Inc. |
| 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 |