Author: Sergei S. Markoff
Date: 01:32:12 03/18/04
Hello!
First try to index history depending of piece that moves. It's a "free"
improvement. I don't know why Crafty not doing it. See me code (it complicated a
little, but works ok):
#define KING 1
#define KNIGHT 2
#define PAWN 3
#define ROOK 5
#define BISHOP 6
#define QUEEN 7
const int history_group[8]={0,0,0,1,0,2,1,3};
int history[4][64*64*2];
<...>
void History(int Depth,MOVE mv)
{
int index=((mv&4095)<<1)|SideToMove;
int index1=history_group[M_PIECE(mv)];
history[index1][index]+=Depth*Depth;
<...>
The second good idea is to right shift history in case of overflow at least.
if(history[index1][index]>=MAX_HISTORY)
{
int i,j;
for(j=0;j<4;j++) for(i=0;i<64*64*2;i++) history[j][i]>>=1;
}
And a last near-free improvement is to include endgame flags into history index.
Or having queens. For example in endgame after queen promotion history values
becomes really unrelevant.
Best wishes,
Sergei.
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