Author: scott farrell
Date: 08:13:13 08/15/03
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On August 13, 2003 at 12:38:40, Johan Wessfeldt wrote:
>Im developing a chess engine in java and Im done with the move-generation.
>Ive run a couple of tests and so far so good. No perf-test failures yet! :]
>
>Ive discovered my Least significant Bit method is really slowing me down tho..
>
>The best Ive come up with so far goes like this:
>
>private int lsb(long a){
>for(int i=63;i>0;i--){
> if( (a & mask[i] ) == mask[i] ){
> return i; }
>}
>return 0;
>}
>
>where mask[] is a vector of all the combinations.. like mask[0] = 0001, mask[1]
>= 00010, mask[3] = 00100 ... and so on.
>
>Ive tried some well known methods but with no results since Java's long(64 bits)
>datatype is signed. It messes up the bits..
>
>(All datatypes in Java are signed)
>
>Anyone have any suggesitons on how to optimize this method?
here is mine (which is java) - look mah - no loops:
let me know what you think, or if yours is better, or you can enhance.
public static int msb(long bitboard){
if (bitboard==0)
return -1;
int w = (int)((bitboard >>> 48) & 65535);
if (w != 0){
return msb_table[w]+48;
}
w = (int)((bitboard >>> 32) & 65535);
if (w != 0){
return msb_table[w]+32;
}
w = (int)((bitboard >>> 16) & 65535);
if (w != 0){
return msb_table[w]+16;
}
w = (int)(bitboard & 65535);
if (w != 0){
return msb_table[w];
}
return -1;
}
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