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Use Carry-Rippler trick to speed up magics

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Nice trick discovered on:

http://chessprogramming.wikispaces.com/Traversing+Subsets+of+a+Set

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2011-06-14 18:40:52 +01:00
parent fc519ca74a
commit 4c9d570e43
1 changed files with 9 additions and 28 deletions
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37
src/bitboard.cpp
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@ -252,25 +252,6 @@ void init_bitboards() {
namespace {
Bitboard submask(Bitboard mask, int key) {
Bitboard b, subMask = 0;
int bitProbe = 1;
// Extract an unique submask out of a mask according to the given key
while (mask)
{
b = mask & -mask;
mask ^= b;
if (key & bitProbe)
subMask |= b;
bitProbe <<= 1;
}
return subMask;
}
Bitboard sliding_attacks(Square sq, Bitboard occupied, Square delta[], Bitboard excluded) {
Bitboard attacks = 0;
@ -321,7 +302,7 @@ namespace {
const int MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 },
{ 1059, 3608, 605, 3234, 3326, 38, 2029, 3043 } };
RKISS rk;
Bitboard occupancy[4096], reference[4096], excluded;
Bitboard occupancy[4096], reference[4096], excluded, b;
int key, maxKey, index, booster, offset = 0;
for (Square s = SQ_A1; s <= SQ_H8; s++)
@ -332,17 +313,17 @@ namespace {
mask[s] = sliding_attacks(s, EmptyBoardBB, delta, excluded);
shift[s] = (CpuIs64Bit ? 64 : 32) - count_1s<CNT32_MAX15>(mask[s]);
maxKey = 1 << count_1s<CNT32_MAX15>(mask[s]);
// Use Carry-Rippler trick to enumerate all subsets of mask[s]
b = maxKey = 0;
do {
occupancy[maxKey] = b;
reference[maxKey++] = sliding_attacks(s, b, delta, EmptyBoardBB);
b = (b - mask[s]) & mask[s];
} while (b);
offset += maxKey;
booster = MagicBoosters[CpuIs64Bit][square_rank(s)];
// First compute occupancy and attacks for square 's'
for (key = 0; key < maxKey; key++)
{
occupancy[key] = submask(mask[s], key);
reference[key] = sliding_attacks(s, occupancy[key], delta, EmptyBoardBB);
}
// Then find a possible magic and the corresponding attacks
do {
magic[s] = pick_magic(mask[s], rk, booster);