Commit 4ec4a8e6 authored by Paul Eggert's avatar Paul Eggert

count-leading-zeros: port to MSC; support types wider than 64 bits

The ideas behind the MSC port are stolen from Emacs.
* lib/count-leading-zeros.h:
Don't include verify.h: it's no longer needed, as types wider than
64 bits are now supported.
(COUNT_LEADING_ZEROS): New arg MSC_BUILTIN, for better
performance with MSC.  All uses changed.  Do not assume that TYPE
has at most 64 bits.
(count_leading_zeros_32): Assume 0 < X < 2**32, for speed.
All uses changed.  Fold the subtraction from 31 into the table.
parent 75588b6e
2013-10-06 Paul Eggert <eggert@cs.ucla.edu>
count-leading-zeros: port to MSC; support types wider than 64 bits
The ideas behind the MSC port are stolen from Emacs.
* lib/count-leading-zeros.h:
Don't include verify.h: it's no longer needed, as types wider than
64 bits are now supported.
(COUNT_LEADING_ZEROS): New arg MSC_BUILTIN, for better
performance with MSC. All uses changed. Do not assume that TYPE
has at most 64 bits.
(count_leading_zeros_32): Assume 0 < X < 2**32, for speed.
All uses changed. Fold the subtraction from 31 into the table.
count-one-bits: port to MSC; support types wider than 64 bits
The ideas behind the MSC port are stolen from Emacs.
* lib/count-one-bits.c (popcount_support) [_MSC_VER]: New variable.
......@@ -17,11 +17,10 @@
/* 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"
#ifndef _GL_INLINE_HEADER_BEGIN
#error "Please include config.h first."
......@@ -31,45 +30,58 @@ _GL_INLINE_HEADER_BEGIN
# define COUNT_LEADING_ZEROS_INLINE _GL_INLINE
#endif
/* 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
/* 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 __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
# define COUNT_LEADING_ZEROS(BUILTIN, TYPE) \
# 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. */
/* 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)
{
/* http://graphics.stanford.edu/~seander/bithacks.html */
static const char deBruijnLookup[32] = {
0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30,
8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31
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 &= 0xffffffffU;
if (!x)
return 32;
x |= x >> 1;
x |= x >> 2;
x |= x >> 4;
x |= x >> 8;
x |= x >> 16;
return 31 - deBruijnLookup[(x * 0x07c4acddU) >> 27];
return de_Bruijn_lookup[((x * 0x07c4acddU) & 0xffffffffU) >> 27];
}
#endif
......@@ -77,14 +89,14 @@ count_leading_zeros_32 (unsigned int x)
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. */
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
......@@ -92,7 +104,8 @@ count_leading_zeros_l (unsigned long int x)
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
......
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