--- /dev/null
+/* 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
--- /dev/null
+/* 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;
+}
projects / gnulib.git / commitdiff