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Remove a local variable from pop_1st_bit()

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Remove the 'b' uint32_t local variable.
Optimized assembly is more or less the same
(one 'mov' instruction less), but now it is
written in a way more similar to the final assembly
flow so it should be easier for compiler to optimize.

Also guarantee that BitTable[] is always aligned.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2009-08-23 17:20:02 +01:00
parent ba04eb0446
commit d1d4437699
1 changed files with 7 additions and 11 deletions
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18
src/bitboard.cpp
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@ -297,6 +297,7 @@ void init_bitboards() {
#if defined(IS_64BIT) && !defined(USE_BSFQ)
CACHE_LINE_ALIGNMENT
static const int BitTable[64] = {
0, 1, 2, 7, 3, 13, 8, 19, 4, 25, 14, 28, 9, 34, 20, 40, 5, 17, 26, 38, 15,
46, 29, 48, 10, 31, 35, 54, 21, 50, 41, 57, 63, 6, 12, 18, 24, 27, 33, 39,
@ -316,6 +317,7 @@ Square pop_1st_bit(Bitboard* b) {
#elif !defined(USE_BSFQ)
CACHE_LINE_ALIGNMENT
static const int BitTable[64] = {
63, 30, 3, 32, 25, 41, 22, 33, 15, 50, 42, 13, 11, 53, 19, 34, 61, 29, 2,
51, 21, 43, 45, 10, 18, 47, 1, 54, 9, 57, 0, 35, 62, 31, 40, 4, 49, 5, 52,
@ -343,23 +345,17 @@ union b_union {
Square pop_1st_bit(Bitboard* bb) {
b_union u;
uint32_t b;
u.b = *bb;
if (u.dw.l)
{
b = u.dw.l;
*((uint32_t*)bb) = b & (b - 1);
b ^= (b - 1);
*((uint32_t*)bb) = u.dw.l & (u.dw.l - 1);
return Square(BitTable[((u.dw.l ^ (u.dw.l - 1)) * 0x783a9b23) >> 26]);
}
else
{
b = u.dw.h;
*((uint32_t*)bb+1) = b & (b - 1); // Little endian only?
b = ~(b ^ (b - 1));
}
return Square(BitTable[(b * 0x783a9b23) >> 26]);
*((uint32_t*)bb+1) = u.dw.h & (u.dw.h - 1); // Little endian only?
return Square(BitTable[((~(u.dw.h ^ (u.dw.h - 1))) * 0x783a9b23) >> 26]);
}
#endif