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/**
Copyright (c) Scott Gasch
Module Name:
sig.c
Abstract:
Position signature code... the algorithm is a Zobrist hash scheme.
Every piece has a different 64-bit "seed" for every different
square. Plus some non-piece/location features of a position (such
as legal castling rights or the en passant location) have 64-bit
"seed" keys. The position's signature is the xor sum of all these
seeds. A position's pawn hash signature is the xor sum of all
pawn-related seeds. These signatures, once computed, can be
incrementally maintained by just xoring off the seed of a moving
piece's from location and xoring on the seed of its to location.
These signatures are used as the basis for the pawn hash and main
transposition table code.
Author:
Scott Gasch ([email protected]) 09 May 2004
Revision History:
$Id: sig.c 345 2007-12-02 22:56:42Z scott $
**/
#include "chess.h"
UINT64 g_u64SigSeeds[128][7][2];
UINT64 g_u64PawnSigSeeds[128][2];
UINT64 g_u64CastleSigSeeds[16];
UINT64 g_u64EpSigSeeds[9];
void
InitializeSigSystem(void)
/**
Routine description:
Populate the arrays of signature keys (see above) used to generate
normal and pawn signatures for POSITIONs.
Parameters:
void
Return value:
void
**/
{
ULONG x, y, z;
UINT uChecksum = 0;
ULONG uRandom;
memset(g_u64SigSeeds, 0, sizeof(g_u64SigSeeds));
memset(g_u64PawnSigSeeds, 0, sizeof(g_u64PawnSigSeeds));
memset(g_u64CastleSigSeeds, 0, sizeof(g_u64CastleSigSeeds));
memset(g_u64EpSigSeeds, 0, sizeof(g_u64EpSigSeeds));
seedMT(2222);
for (x = A; x <= H+1; x++)
{
//
// Do en-passant sig
//
uRandom = randomMT();
uChecksum ^= uRandom;
g_u64EpSigSeeds[x] = (UINT64)uRandom << 32;
uRandom = randomMT();
uChecksum ^= uRandom;
g_u64EpSigSeeds[x] |= uRandom;
g_u64EpSigSeeds[x] &= ~1;
}
//
// Foreach square on the board.
//
for (x = 0; x < 128; x++)
{
//
// For both colors
//
FOREACH_COLOR(z)
{
//
// Do the pawn sigs
//
uRandom = randomMT();
uChecksum ^= uRandom;
g_u64PawnSigSeeds[x][z] = (UINT64)uRandom << 32;
uRandom = randomMT();
uChecksum ^= uRandom;
g_u64PawnSigSeeds[x][z] |= uRandom;
g_u64PawnSigSeeds[x][z] &= ~1;
//
// Do the piece sigs
//
for (y = 0; y < 7; y++)
{
uRandom = randomMT();
uChecksum ^= uRandom;
g_u64SigSeeds[x][y][z] = (UINT64)uRandom << 32;
uRandom = randomMT();
uChecksum ^= uRandom;
g_u64SigSeeds[x][y][z] |= uRandom;
g_u64SigSeeds[x][y][z] &= ~1;
}
}
}
//
// For all castle permissions
//
for (x = 0; x < 16; x++)
{
uRandom = randomMT();
uChecksum ^= uRandom;
g_u64CastleSigSeeds[x] = (UINT64)uRandom << 32;
uRandom = randomMT();
uChecksum ^= uRandom;
g_u64CastleSigSeeds[x] |= uRandom;
g_u64CastleSigSeeds[x] &= ~1;
}
//
// Make sure we got what we expected.
//
if (uChecksum != 0xac19ab2b)
{
UtilPanic(DETECTED_INCORRECT_INITIALIZATION,
NULL,
"signature system",
(void *)uChecksum,
(void *)0xac19ab2b,
__FILE__, __LINE__);
}
}
UINT64
ComputePawnSig(POSITION *pos)
/**
Routine description:
Given a board, recompute the pawn signature from scratch.
Parameters:
POSITION *pos
Return value:
UINT64
**/
{
register COOR c;
PIECE p;
UINT64 u64Sum = 0;
FOREACH_SQUARE(c)
{
if (!IS_ON_BOARD(c)) continue;
p = pos->rgSquare[c].pPiece;
if (IS_PAWN(p))
{
u64Sum ^= g_u64PawnSigSeeds[c][GET_COLOR(p)];
}
}
return(u64Sum);
}
UINT64
ComputeSig(POSITION *pos)
/**
Routine description:
Given a board, recompute the main signature from scratch.
Parameters:
POSITION *pos
Return value:
UINT64
**/
{
register COOR c;
UINT64 u64Sum = 0;
PIECE p;
FOREACH_SQUARE(c)
{
if (!IS_ON_BOARD(c)) continue;
p = pos->rgSquare[c].pPiece;
if (!IS_EMPTY(p) && !IS_PAWN(p))
{
ASSERT(IS_VALID_PIECE(p));
u64Sum ^= g_u64SigSeeds[c][PIECE_TYPE(p)][GET_COLOR(p)];
}
}
//
// Update the signature to reflect the castle permissions and ep
// square at this point.
//
u64Sum ^= g_u64CastleSigSeeds[pos->bvCastleInfo];
u64Sum ^= g_u64EpSigSeeds[FILE(pos->cEpSquare)];
//
// Update the low order bit to reflect the side to move.
//
if (pos->uToMove == WHITE)
{
u64Sum |= 1;
}
else
{
u64Sum &= ~1;
}
ASSERT((u64Sum & 1) == pos->uToMove);
return(u64Sum);
}
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