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Move POPCOUNTL to cogl-util

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This moves the POPCOUNTL macro from cogl-winsys-glx to cogl-util and
renames it to _cogl_util_popcountl so that it can be used in more
places. The fallback function for when the GCC builtin is not
available has been replaced with an 8-bit lookup table because the
HAKMEM implementation doesn't look like it would work when longs are
64-bit so it's not suitable for a general purpose function on 64-bit
architectures. Some of the pages regarding population counts seem to
suggest that using a lookup table is the fastest method anyway.

Reviewed-by: Robert Bragg <robert@linux.intel.com>
This commit is contained in:
Neil Roberts
2011-11-01 13:10:59 +00:00
parent 436a7a45da
commit 037c0aa88c
3 changed files with 55 additions and 20 deletions
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34
cogl/cogl-util.h
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@ -100,6 +100,12 @@ _cogl_util_one_at_a_time_hash (unsigned int hash,
unsigned int
_cogl_util_one_at_a_time_mix (unsigned int hash);
/* These two builtins are available since GCC 3.4 */
#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
#define COGL_UTIL_HAVE_BUILTIN_FFSL
#define COGL_UTIL_HAVE_BUILTIN_POPCOUNTL
#endif
/* The 'ffs' function is part of C99 so it isn't always available */
#ifdef HAVE_FFS
#define _cogl_util_ffs ffs
@ -110,9 +116,8 @@ _cogl_util_ffs (int num);
/* The 'ffsl' function is non-standard but GCC has a builtin for it
since 3.4 which we can use */
#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
#ifdef COGL_UTIL_HAVE_BUILTIN_FFSL
#define _cogl_util_ffsl __builtin_ffsl
#define COGL_UTIL_HAVE_BUILTIN_FFSL
#else
/* If ints and longs are the same size we can just use ffs. Hopefully
the compiler will optimise away this conditional */
@ -121,7 +126,30 @@ _cogl_util_ffs (int num);
_cogl_util_ffsl_wrapper (x))
int
_cogl_util_ffsl_wrapper (long int num);
#endif
#endif /* COGL_UTIL_HAVE_BUILTIN_FFSL */
#ifdef COGL_UTIL_HAVE_BUILTIN_POPCOUNTL
#define _cogl_util_popcountl __builtin_popcountl
#else
extern const unsigned char _cogl_util_popcount_table[256];
/* There are many ways of doing popcount but doing a table lookup
seems to be the most robust against different sizes for long. Some
pages seem to claim it's the fastest method anyway. */
static inline int
_cogl_util_popcountl (unsigned long num)
{
int i;
int sum = 0;
/* Let's hope GCC will unroll this loop.. */
for (i = 0; i < sizeof (num); i++)
sum += _cogl_util_popcount_table[(num >> (i * 8)) & 0xff];
return sum;
}
#endif /* COGL_UTIL_HAVE_BUILTIN_POPCOUNTL */
#ifdef COGL_HAS_GLIB_SUPPORT
#define _COGL_RETURN_IF_FAIL(EXPR) g_return_if_fail(EXPR)