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115 lines
4.4 KiB
C
115 lines
4.4 KiB
C
/* count-trailing-zeros.h -- counts the number of trailing 0 bits in a word.
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Copyright 2013-2021 Free Software Foundation, Inc.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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/* Written by Paul Eggert. */
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#ifndef COUNT_TRAILING_ZEROS_H
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#define COUNT_TRAILING_ZEROS_H 1
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#include <limits.h>
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#include <stdlib.h>
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#ifndef _GL_INLINE_HEADER_BEGIN
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#error "Please include config.h first."
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#endif
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_GL_INLINE_HEADER_BEGIN
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#ifndef COUNT_TRAILING_ZEROS_INLINE
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# define COUNT_TRAILING_ZEROS_INLINE _GL_INLINE
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#endif
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#ifdef __cplusplus
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extern "C" {
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#endif
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/* Assuming the GCC builtin is BUILTIN and the MSC builtin is MSC_BUILTIN,
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expand to code that computes the number of trailing zeros of the local
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variable 'x' of type TYPE (an unsigned integer type) and return it
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from the current function. */
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#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) \
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|| (__clang_major__ >= 4)
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# define COUNT_TRAILING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \
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return x ? BUILTIN (x) : CHAR_BIT * sizeof x;
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#elif _MSC_VER
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# pragma intrinsic _BitScanForward
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# pragma intrinsic _BitScanForward64
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# define COUNT_TRAILING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \
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do \
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{ \
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unsigned long result; \
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return MSC_BUILTIN (&result, x) ? result : CHAR_BIT * sizeof x; \
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} \
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while (0)
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#else
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# define COUNT_TRAILING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \
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do \
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{ \
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int count = 0; \
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if (! x) \
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return CHAR_BIT * sizeof x; \
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for (count = 0; \
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(count < CHAR_BIT * sizeof x - 32 \
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&& ! (x & 0xffffffffU)); \
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count += 32) \
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x = x >> 31 >> 1; \
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return count + count_trailing_zeros_32 (x); \
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} \
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while (0)
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/* Compute and return the number of trailing zeros in the least
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significant 32 bits of X. One of these bits must be nonzero. */
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COUNT_TRAILING_ZEROS_INLINE int
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count_trailing_zeros_32 (unsigned int x)
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{
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/* <https://github.com/gibsjose/BitHacks>
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<https://www.fit.vutbr.cz/~ibarina/pub/bithacks.pdf> */
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static const char de_Bruijn_lookup[32] = {
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0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
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31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
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};
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return de_Bruijn_lookup[(((x & -x) * 0x077cb531U) & 0xffffffffU) >> 27];
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}
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#endif
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/* Compute and return the number of trailing zeros in X. */
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COUNT_TRAILING_ZEROS_INLINE int
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count_trailing_zeros (unsigned int x)
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{
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COUNT_TRAILING_ZEROS (__builtin_ctz, _BitScanForward, unsigned int);
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}
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/* Compute and return the number of trailing zeros in X. */
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COUNT_TRAILING_ZEROS_INLINE int
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count_trailing_zeros_l (unsigned long int x)
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{
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COUNT_TRAILING_ZEROS (__builtin_ctzl, _BitScanForward, unsigned long int);
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}
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/* Compute and return the number of trailing zeros in X. */
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COUNT_TRAILING_ZEROS_INLINE int
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count_trailing_zeros_ll (unsigned long long int x)
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{
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COUNT_TRAILING_ZEROS (__builtin_ctzll, _BitScanForward64,
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unsigned long long int);
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}
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#ifdef __cplusplus
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}
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#endif
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_GL_INLINE_HEADER_END
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#endif
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