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/* count-trailing-zeros.h -- counts the number of trailing 0 bits in a word.
Copyright 2013-2020 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* Written by Paul Eggert. */
#ifndef COUNT_TRAILING_ZEROS_H
#define COUNT_TRAILING_ZEROS_H 1
#include <limits.h>
#include <stdlib.h>
#ifndef _GL_INLINE_HEADER_BEGIN
#error "Please include config.h first."
#endif
_GL_INLINE_HEADER_BEGIN
#ifndef COUNT_TRAILING_ZEROS_INLINE
# define COUNT_TRAILING_ZEROS_INLINE _GL_INLINE
#endif
#ifdef __cplusplus
extern "C" {
#endif
/* Assuming the GCC builtin is BUILTIN and the MSC builtin is MSC_BUILTIN,
expand to code that computes the number of trailing zeros of the local
variable 'x' of type TYPE (an unsigned integer type) and return it
from the current function. */
#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) \
|| (__clang_major__ >= 4)
# define COUNT_TRAILING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \
return x ? BUILTIN (x) : CHAR_BIT * sizeof x;
#elif _MSC_VER
# pragma intrinsic _BitScanForward
# pragma intrinsic _BitScanForward64
# define COUNT_TRAILING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \
do \
{ \
unsigned long result; \
return MSC_BUILTIN (&result, x) ? result : CHAR_BIT * sizeof x; \
} \
while (0)
#else
# define COUNT_TRAILING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \
do \
{ \
int count = 0; \
if (! x) \
return CHAR_BIT * sizeof x; \
for (count = 0; \
(count < CHAR_BIT * sizeof x - 32 \
&& ! (x & 0xffffffffU)); \
count += 32) \
x = x >> 31 >> 1; \
return count + count_trailing_zeros_32 (x); \
} \
while (0)
/* Compute and return the number of trailing zeros in the least
significant 32 bits of X. One of these bits must be nonzero. */
COUNT_TRAILING_ZEROS_INLINE int
count_trailing_zeros_32 (unsigned int x)
{
/* <https://github.com/gibsjose/BitHacks>
<https://www.fit.vutbr.cz/~ibarina/pub/bithacks.pdf> */
static const char de_Bruijn_lookup[32] = {
0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
};
return de_Bruijn_lookup[(((x & -x) * 0x077cb531U) & 0xffffffffU) >> 27];
}
#endif
/* Compute and return the number of trailing zeros in X. */
COUNT_TRAILING_ZEROS_INLINE int
count_trailing_zeros (unsigned int x)
{
COUNT_TRAILING_ZEROS (__builtin_ctz, _BitScanForward, unsigned int);
}
/* Compute and return the number of trailing zeros in X. */
COUNT_TRAILING_ZEROS_INLINE int
count_trailing_zeros_l (unsigned long int x)
{
COUNT_TRAILING_ZEROS (__builtin_ctzl, _BitScanForward, unsigned long int);
}
/* Compute and return the number of trailing zeros in X. */
COUNT_TRAILING_ZEROS_INLINE int
count_trailing_zeros_ll (unsigned long long int x)
{
COUNT_TRAILING_ZEROS (__builtin_ctzll, _BitScanForward64,
unsigned long long int);
}
#ifdef __cplusplus
}
#endif
_GL_INLINE_HEADER_END
#endif
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