mirror of
https://git.savannah.gnu.org/git/emacs.git
synced 2024-12-11 09:20:51 +00:00
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.
|
|
Copyright 2013-2021 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
|