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[PATCH 2/3] count-leading-zeros: port to MSC; support types wider than 6
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From: |
Paul Eggert |
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Subject: |
[PATCH 2/3] count-leading-zeros: port to MSC; support types wider than 64 bits |
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Date: |
Mon, 07 Oct 2013 00:01:18 -0700 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.0 |
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.
---
ChangeLog | 11 ++++++++
lib/count-leading-zeros.h | 69 ++++++++++++++++++++++++++++-------------------
2 files changed, 52 insertions(+), 28 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 3d4f38d..9e80e07 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,16 @@
2013-10-06 Paul Eggert <address@hidden>
+ 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.
diff --git a/lib/count-leading-zeros.h b/lib/count-leading-zeros.h
index 204fa5a..0a04fc8 100644
--- a/lib/count-leading-zeros.h
+++ b/lib/count-leading-zeros.h
@@ -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
--
1.8.3.1