/* count-leading-zeros.h -- counts the number of leading 0 bits in a word.
- Copyright (C) 2012 Free Software Foundation, Inc.
+ Copyright (C) 2012-2014 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
/* Written by Eric Blake. */
#ifndef COUNT_LEADING_ZEROS_H
-# define COUNT_LEADING_ZEROS_H 1
+#define COUNT_LEADING_ZEROS_H 1
#include <limits.h>
#include <stdlib.h>
-#include "verify.h"
-/* Expand the code which computes the number of leading zeros of the local
- variable 'x' of type TYPE (an unsigned integer type) and returns it
+#ifndef _GL_INLINE_HEADER_BEGIN
+ #error "Please include config.h first."
+#endif
+_GL_INLINE_HEADER_BEGIN
+#ifndef COUNT_LEADING_ZEROS_INLINE
+# define COUNT_LEADING_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 leading zeros of the local
+ variable 'x' of type TYPE (an unsigned integer type) and return it
from the current function. */
-#if 0 && __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
-# define COUNT_LEADING_ZEROS(BUILTIN, TYPE) \
+#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
+# define COUNT_LEADING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \
return x ? BUILTIN (x) : CHAR_BIT * sizeof x;
+#elif _MSC_VER
+# pragma intrinsic _BitReverse
+# pragma intrinsic _BitReverse64
+# define COUNT_LEADING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \
+ do \
+ { \
+ unsigned long result; \
+ return MSC_BUILTIN (&result, x) ? result : CHAR_BIT * sizeof x; \
+ } \
+ while (0)
#else
-# define COUNT_LEADING_ZEROS(BUILTIN, TYPE) \
- /* This condition is written so as to avoid shifting by more than \
- 31 bits at once, and also avoids a random HP-UX cc bug. */ \
- verify (((TYPE) -1 >> 31 >> 31 >> 2) == 0); /* TYPE has at most 64 bits */ \
- int count = 0; \
- if (1 < (TYPE) -1 >> 31) { /* TYPE has more than 32 bits? */ \
- count = count_leading_zeros_32 (x >> 31 >> 1); \
- if (count < 32) \
- return count; \
- } \
- return count + count_leading_zeros_32 (x);
+# define COUNT_LEADING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE) \
+ do \
+ { \
+ int count; \
+ unsigned int leading_32; \
+ if (! x) \
+ return CHAR_BIT * sizeof x; \
+ for (count = 0; \
+ (leading_32 = ((x >> (sizeof (TYPE) * CHAR_BIT - 32)) \
+ & 0xffffffffU), \
+ count < CHAR_BIT * sizeof x - 32 && !leading_32); \
+ count += 32) \
+ x = x << 31 << 1; \
+ return count + count_leading_zeros_32 (leading_32); \
+ } \
+ while (0)
-/* Compute and return the number of leading zeros in the least
- significant 32 bits of X. */
-static inline int
+/* Compute and return the number of leading zeros in X,
+ where 0 < X < 2**32. */
+COUNT_LEADING_ZEROS_INLINE int
count_leading_zeros_32 (unsigned int x)
{
- int count = 0;
- if (x & 0xffff0000U)
- x >>= 16;
- else
- count += 16;
- if (x & 0xff00)
- x >>= 8;
- else
- count += 8;
- if (x & 0xf0)
- x >>= 4;
- else
- count += 4;
- if (x & 0xc)
- x >>= 2;
- else
- count += 2;
- if (x & 2)
- x >>= 1;
- else
- count++;
- if (!(x & 1))
- count++;
- return count;
+ /* http://graphics.stanford.edu/~seander/bithacks.html */
+ static const char de_Bruijn_lookup[32] = {
+ 31, 22, 30, 21, 18, 10, 29, 2, 20, 17, 15, 13, 9, 6, 28, 1,
+ 23, 19, 11, 3, 16, 14, 7, 24, 12, 4, 8, 25, 5, 26, 27, 0
+ };
+
+ x |= x >> 1;
+ x |= x >> 2;
+ x |= x >> 4;
+ x |= x >> 8;
+ x |= x >> 16;
+ return de_Bruijn_lookup[((x * 0x07c4acddU) & 0xffffffffU) >> 27];
}
#endif
/* Compute and return the number of leading zeros in X. */
-static inline int
+COUNT_LEADING_ZEROS_INLINE int
count_leading_zeros (unsigned int x)
{
- COUNT_LEADING_ZEROS (__builtin_clz, unsigned int);
+ COUNT_LEADING_ZEROS (__builtin_clz, _BitScanReverse, unsigned int);
}
/* Compute and return the number of leading zeros in X. */
-static inline int
+COUNT_LEADING_ZEROS_INLINE int
count_leading_zeros_l (unsigned long int x)
{
- COUNT_LEADING_ZEROS (__builtin_clzl, unsigned long int);
+ COUNT_LEADING_ZEROS (__builtin_clzl, _BitScanReverse, unsigned long int);
}
#if HAVE_UNSIGNED_LONG_LONG_INT
/* Compute and return the number of leading zeros in X. */
-static inline int
+COUNT_LEADING_ZEROS_INLINE int
count_leading_zeros_ll (unsigned long long int x)
{
- COUNT_LEADING_ZEROS (__builtin_clzll, unsigned long long int);
+ COUNT_LEADING_ZEROS (__builtin_clzll, _BitScanReverse64,
+ unsigned long long int);
}
#endif
+_GL_INLINE_HEADER_END
+
#endif /* COUNT_LEADING_ZEROS_H */
projects / gnulib.git / blobdiff