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Code Issues Releases Wiki Activity

Optimized bitScanReverse32()

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Should be a bit faster then previous one.
Hacked by Pascal Georges.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2009-12-29 14:43:15 +01:00
parent cf486cf229
commit 990d83a72d
1 changed files with 22 additions and 11 deletions
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33
src/bitboard.cpp
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@ -368,27 +368,38 @@ Square pop_1st_bit(Bitboard* bb) {
#endif #endif
// Optimized bitScanReverse32() implementation by Pascal Georges. Note
// that first bit is 1, this allow to differentiate between 0 and 1.
static CACHE_LINE_ALIGNMENT
const char MsbTable[256] = {
0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5,
5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8
};
int bitScanReverse32(uint32_t b) int bitScanReverse32(uint32_t b)
{ {
int result = 0; int result = 0;
if (b > 0xFFFF) { if (b > 0xFFFF)
{
b >>= 16; b >>= 16;
result += 16; result += 16;
} }
if (b > 0xFF) { if (b > 0xFF)
{
b >>= 8; b >>= 8;
result += 8; result += 8;
} }
if (b > 0xF) { return result + MsbTable[b];
b >>= 4;
result += 4;
}
if (b > 0x3) {
b >>= 2;
result += 2;
}
return result + (b > 0) + (b > 1);
} }
namespace { namespace {