Commit 0a47086e authored by Paul Eggert's avatar Paul Eggert

New module 'count-trailing-zeros'.

* MODULES.html.sh: Mention it.
* lib/count-trailing-zeros.c, lib/count-trailing-zeros.h:
* m4/count-trailing-zeros.m4, modules/count-trailing-zeros:
* modules/count-trailing-zeros-tests:
* tests/test-count-trailing-zeros.c:
New files.
parent 4ec4a8e6
2013-10-06 Paul Eggert <eggert@cs.ucla.edu> 2013-10-06 Paul Eggert <eggert@cs.ucla.edu>
New module 'count-trailing-zeros'.
* MODULES.html.sh: Mention it.
* lib/count-trailing-zeros.c, lib/count-trailing-zeros.h:
* m4/count-trailing-zeros.m4, modules/count-trailing-zeros:
* modules/count-trailing-zeros-tests:
* tests/test-count-trailing-zeros.c:
New files.
count-leading-zeros: port to MSC; support types wider than 64 bits count-leading-zeros: port to MSC; support types wider than 64 bits
The ideas behind the MSC port are stolen from Emacs. The ideas behind the MSC port are stolen from Emacs.
* lib/count-leading-zeros.h: * lib/count-leading-zeros.h:
...@@ -1757,6 +1757,7 @@ func_all_modules () ...@@ -1757,6 +1757,7 @@ func_all_modules ()
func_begin_table func_begin_table
func_module count-leading-zeros func_module count-leading-zeros
func_module count-one-bits func_module count-one-bits
func_module count-trailing-zeros
func_module ffs func_module ffs
func_module ffsl func_module ffsl
func_module ffsll func_module ffsll
......
#include <config.h>
#define COUNT_TRAILING_ZEROS_INLINE _GL_EXTERN_INLINE
#include "count-trailing-zeros.h"
/* count-trailing-zeros.h -- counts the number of trailing 0 bits in a word.
Copyright 2013 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 <http://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
/* 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)
# 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)
{
/* http://graphics.stanford.edu/~seander/bithacks.html */
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);
}
#if HAVE_UNSIGNED_LONG_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);
}
#endif
_GL_INLINE_HEADER_END
#endif
# count-trailing-zeros.m4
dnl Copyright (C) 2013 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.
AC_DEFUN([gl_COUNT_TRAILING_ZEROS],
[
dnl We don't need (and can't compile) count_trailing_zeros_ll
dnl unless the type 'unsigned long long int' exists.
AC_REQUIRE([AC_TYPE_UNSIGNED_LONG_LONG_INT])
])
Description:
Counts the number of trailing 0-bits in a word.
Files:
lib/count-trailing-zeros.c
lib/count-trailing-zeros.h
m4/count-trailing-zeros.m4
Depends-on:
extern-inline
configure.ac:
gl_COUNT_TRAILING_ZEROS
Makefile.am:
lib_SOURCES += count-trailing-zeros.c
Include:
"count-trailing-zeros.h"
License:
LGPLv2+
Maintainer:
all
Files:
tests/test-count-trailing-zeros.c
tests/macros.h
Depends-on:
configure.ac:
Makefile.am:
TESTS += test-count-trailing-zeros
check_PROGRAMS += test-count-trailing-zeros
/* Test counting of trailing zeros.
Copyright (C) 2013 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 <http://www.gnu.org/licenses/>. */
/* Written by Paul Eggert. */
#include <config.h>
#include "count-trailing-zeros.h"
#include <limits.h>
#include <stdio.h>
#include "macros.h"
#define UINT_BIT (sizeof (unsigned int) * CHAR_BIT)
#define ULONG_BIT (sizeof (unsigned long int) * CHAR_BIT)
#define ULLONG_BIT (sizeof (unsigned long long int) * CHAR_BIT)
#ifndef ULLONG_MAX
# define HALF (1ULL << (sizeof (unsigned long long int) * CHAR_BIT - 1))
# define ULLONG_MAX (HALF - 1 + HALF)
#endif
int
main (int argc, char *argv[])
{
int i, j;
#define TEST_COUNT_TRAILING_ZEROS(FUNC, TYPE, BITS, MAX, ONE) \
ASSERT (FUNC (0) == BITS); \
for (i = 0; i < BITS; i++) \
{ \
ASSERT (FUNC (ONE << i) == i); \
for (j = 0; j < i; j++) \
ASSERT (FUNC ((ONE << i) | (ONE << j)) == j); \
} \
for (i = 0; i < 1000; i++) \
{ \
TYPE value = rand () ^ (rand () << 31 << 1); \
int count = 0; \
for (j = BITS - 1; 0 <= j; j--) \
if (value & (ONE << j)) \
count = j; \
ASSERT (count == FUNC (value)); \
} \
ASSERT (FUNC (MAX) == 0);
TEST_COUNT_TRAILING_ZEROS (count_trailing_zeros, unsigned int,
UINT_BIT, UINT_MAX, 1U);
TEST_COUNT_TRAILING_ZEROS (count_trailing_zeros_l, unsigned long int,
ULONG_BIT, ULONG_MAX, 1UL);
#ifdef HAVE_UNSIGNED_LONG_LONG_INT
TEST_COUNT_TRAILING_ZEROS (count_trailing_zeros_ll, unsigned long long int,
ULLONG_BIT, ULLONG_MAX, 1ULL);
#endif
return 0;
}
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment