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Move magic random to RKISS

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When initializing the magic numbers used to
compute sliding attacks, we endless generate a
random and test it as a possible magic.

In the general case this takes a lot of iterations,
but here, insteaad of picking a casual random, we
rotate it a couple of times and generate a number that
we know has a good probability to be a magic candidate.

This is becuase the quantities by which we rotate the
number are known in advance to produce quickly a good
canidate.

The patch, inspired by DON, just moves the shuffle to RKISS
changing the boosters to take in account a left rotation
instead of a right rotation as in the original.

No functional change.
This commit is contained in:
Marco Costalba 2014-02-12 14:47:36 +01:00
parent b534176d4a
commit e6523e56b8
2 changed files with 12 additions and 17 deletions
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21
src/bitboard.cpp
View file

@ -246,20 +246,6 @@ namespace {
}
Bitboard pick_random(RKISS& rk, int booster) {
// Values s1 and s2 are used to rotate the candidate magic of a
// quantity known to be optimal to quickly find the magics.
int s1 = booster & 63, s2 = (booster >> 6) & 63;
Bitboard m = rk.rand<Bitboard>();
m = (m >> s1) | (m << (64 - s1));
m &= rk.rand<Bitboard>();
m = (m >> s2) | (m << (64 - s2));
return m & rk.rand<Bitboard>();
}
// init_magics() computes all rook and bishop attacks at startup. Magic
// bitboards are used to look up attacks of sliding pieces. As a reference see
// chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
@ -268,8 +254,9 @@ namespace {
void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
Bitboard masks[], unsigned shifts[], Square deltas[], Fn index) {
int MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 },
{ 1059, 3608, 605, 3234, 3326, 38, 2029, 3043 } };
int MagicBoosters[][8] = { { 969, 1976, 2850, 542, 2069, 2852, 1708, 164 },
{ 3101, 552, 3555, 926, 834, 4122, 2131, 1117 } };
RKISS rk;
Bitboard occupancy[4096], reference[4096], edges, b;
int i, size, booster;
@ -309,7 +296,7 @@ namespace {
// Find a magic for square 's' picking up an (almost) random number
// until we find the one that passes the verification test.
do {
do magics[s] = pick_random(rk, booster);
do magics[s] = rk.magic_rand<Bitboard>(booster);
while (popcount<Max15>((magics[s] * masks[s]) >> 56) < 6);
std::memset(attacks[s], 0, size * sizeof(Bitboard));

8
src/rkiss.h
View file

@ -68,6 +68,14 @@ public:
}
template<typename T> T rand() { return T(rand64()); }
/// Special generator used to fast init magic numbers. Here the
/// trick is to rotate the randoms of a given quantity 's' known
/// to be optimal to quickly find a good magic candidate.
template<typename T> T magic_rand(int s) {
return rotate_L(rotate_L(rand<T>(), (s >> 0) & 0x3F) & rand<T>()
, (s >> 6) & 0x3F) & rand<T>();
}
};
#endif // #ifndef RKISS_H_INCLUDED