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Move magic random to RKISS

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.
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1 parent b534176 commit e6523e56b8cc110aa38d698a993cb04b430e67b0 @mcostalba committed Feb 12, 2014
Showing with 12 additions and 17 deletions.
  1. +4 −17 src/bitboard.cpp
  2. +8 −0 src/rkiss.h
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@@ -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));
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@@ -68,6 +68,14 @@ class RKISS {
}
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

2 comments on commit e6523e5

Just curious -- why not generate the magic multipliers and attack tables and store it on disk so that Stockfish doesn't have to compute them on startup every time? I am sorry if this has been answered before or addressed in code comments.

Owner

mcostalba replied Feb 12, 2014

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