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Use double rotate for magic generation

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Allow to choose among 4096 instances of pseudo-random
sequences instead of the previous 64 so the probability
to find a better sequence increases and actually we have
a much better 64 bit case and we can also use the 64 bit
version of pick_magic() also for 32 bits and althoug sub
optimal, because now we can have more choices results are
even slightly better also for 32 bit.

Use also a faster submask().

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2011-06-09 18:09:19 +01:00
parent e0215f3222
commit b414fc0dfd
1 changed files with 23 additions and 15 deletions
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38
src/bitboard.cpp
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@ -255,13 +255,20 @@ namespace {
Bitboard submask(Bitboard mask, int key) {
Bitboard subMask = 0;
int bitNum = -1;
Bitboard b, subMask = 0;
int bitProbe = 1;
// Extract an unique submask out of a mask according to the given key
for (Square s = SQ_A1; s <= SQ_H8; s++)
if (bit_is_set(mask, s) && bit_is_set(key, Square(++bitNum)))
set_bit(&subMask, s);
while (mask)
{
b = mask & -mask;
mask ^= b;
if (key & bitProbe)
subMask |= b;
bitProbe <<= 1;
}
return subMask;
}
@ -289,20 +296,21 @@ namespace {
return attacks;
}
template<bool Is64>
Bitboard pick_magic(Bitboard mask, RKISS& rk, int booster) {
Bitboard magic;
// Advance PRNG state of a quantity known to be the optimal to
// quickly retrieve all the magics.
for (int i = 0; i < booster; i++)
rk.rand<Bitboard>();
// Values s1 and s2 are used to rotate the candidate magic of
// a quantity known to be the optimal to quickly find the magics.
int s1 = booster & 63, s2 = (booster >> 6) & 63;
while (true)
{
magic = rk.rand<Bitboard>() & rk.rand<Bitboard>();
magic &= Is64 ? rk.rand<Bitboard>() : (rk.rand<Bitboard>() | rk.rand<Bitboard>());
magic = rk.rand<Bitboard>();
magic = (magic >> s1) | (magic << (64 - s1));
magic &= rk.rand<Bitboard>();
magic = (magic >> s2) | (magic << (64 - s2));
magic &= rk.rand<Bitboard>();
if (BitCount8Bit[(mask * magic) >> 56] >= 6)
return magic;
@ -312,8 +320,8 @@ namespace {
void init_sliding_attacks(Bitboard magic[], Bitboard* attack[], Bitboard attTable[],
Bitboard mask[], int shift[], Square delta[]) {
const int MagicBoosters[][8] = { { 55, 11, 17, 2, 39, 3, 31, 44 },
{ 26, 21, 21, 32, 31, 9, 5, 11 } };
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;
int key, maxKey, index, booster, offset = 0;
@ -339,7 +347,7 @@ namespace {
// Then find a possible magic and the corresponding attacks
do {
magic[s] = pick_magic<CpuIs64Bit>(mask[s], rk, booster);
magic[s] = pick_magic(mask[s], rk, booster);
memset(attack[s], 0, maxKey * sizeof(Bitboard));
for (key = 0; key < maxKey; key++)