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Add _hb_bit_storage()

This commit is contained in:
Behdad Esfahbod 2010-05-20 15:31:12 +01:00
parent 6b1b957f6d
commit 9b60233385
1 changed files with 22 additions and 13 deletions
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35
src/hb-private.h
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@ -136,27 +136,36 @@
#endif #endif
/* Return the number of 1 bits in mask. /* Return the number of 1 bits in mask. */
*
* GCC 3.4 supports a "population count" builtin, which on many targets is
* implemented with a single instruction. There is a fallback definition
* in libgcc in case a target does not have one, which should be just as
* good as the open-coded solution below, (which is "HACKMEM 169").
*/
static inline HB_CONST_FUNC unsigned int static inline HB_CONST_FUNC unsigned int
_hb_popcount32 (uint32_t mask) _hb_popcount32 (uint32_t mask)
{ {
#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) #if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
return __builtin_popcount (mask); return __builtin_popcount (mask);
#else #else
register uint32_t y; /* "HACKMEM 169" */
register uint32_t y;
y = (mask >> 1) &033333333333; y = (mask >> 1) &033333333333;
y = mask - y - ((y >>1) & 033333333333); y = mask - y - ((y >>1) & 033333333333);
return (((y + (y >> 3)) & 030707070707) % 077); return (((y + (y >> 3)) & 030707070707) % 077);
#endif #endif
} }
/* Returns the number of bits needed to store number */
static inline HB_CONST_FUNC unsigned int
_hb_bit_storage (unsigned int number)
{
#if defined(__GNUC__) && (__GNUC__ >= 4) && defined(__OPTIMIZE__)
return likely (number) ? (sizeof (unsigned int) * 8 - __builtin_clzl(number)) : 0;
#else
register unsigned int n_bits = 0;
while (number) {
n_bits++;
number >>= 1;
}
return n_bits;
#endif
}
/* We need external help for these */ /* We need external help for these */