kate/BadFish
1
0
Fork 0
mirror of https://github.com/sockspls/badfish synced 2025-04-30 16:53:09 +00:00
Code Issues Releases Wiki Activity

Fix fragile code to use proper random 64 bit keys.

Browse source 
This fixes an old issue where we want to make a position unique but only
change a small number of bits in the key instead of all 64 of them randomly.
This is fragile and can lead to non uniqueness issues in the TT.

Key make_key(uint64_t seed) takes any integer and produces a unique random 64 bit key.
It is computationally efficient and is based on a congruential pseudo random number
generator using well tested constants by Donald Knuth
(see https://en.wikipedia.org/wiki/Linear_congruential_generator)

STC https://tests.stockfishchess.org/tests/view/5ef6c78f761b685b4c724bb6
LLR: 2.95 (-2.94,2.94) {-1.50,0.50}
Total: 154320 W: 29343 L: 29376 D: 95601
Ptnml(0-2): 2543, 18170, 35891, 17889, 2667

LTC https://tests.stockfishchess.org/tests/view/5ef7d1a9020eec13834a940e
LLR: 2.95 (-2.94,2.94) {-1.50,0.50}
Total: 53488 W: 6629 L: 6584 D: 40275
Ptnml(0-2): 372, 4878, 16183, 4955, 356

closes https://github.com/official-stockfish/Stockfish/pull/2773

bench: 4626776
This commit is contained in:
mstembera 2020-06-26 17:26:46 -07:00 • committed by Joost VandeVondele
parent ca41ee6632
commit de24fcebc8
2 changed files with 6 additions and 1 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
src/search.cpp
View file

@ -662,7 +662,7 @@ namespace {
// search to overwrite a previous full search TT value, so we use a different
// position key in case of an excluded move.
excludedMove = ss->excludedMove;
posKey = pos.key() ^ (Key(excludedMove) << 48); // Isn't a very good hash
posKey = excludedMove == MOVE_NONE ? pos.key() : pos.key() ^ make_key(excludedMove);
tte = TT.probe(posKey, ttHit);
ttValue = ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE;
ttMove = rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0]

5
src/types.h
View file

@ -455,6 +455,11 @@ constexpr bool is_ok(Move m) {
return from_sq(m) != to_sq(m); // Catch MOVE_NULL and MOVE_NONE
}
/// Based on a congruential pseudo random number generator
constexpr Key make_key(uint64_t seed) {
return seed * 6364136223846793005ULL + 1442695040888963407ULL;
}
#endif // #ifndef TYPES_H_INCLUDED
#include "tune.h" // Global visibility to tuning setup