Merge tag 'snapshot-start' into stable

[gnulib.git] / lib / count-trailing-zeros.h

diff --git a/lib/count-trailing-zeros.h b/lib/count-trailing-zeros.h
new file mode 100644 (file)
index 0000000..8b65301
--- /dev/null
+++ b/lib/count-trailing-zeros.h
@@ -0,0 +1,106 @@
+/* count-trailing-zeros.h -- counts the number of trailing 0 bits in a word.
+   Copyright 2013-2014 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