Pre computed look up tables

[acetylmine]

//some code for the generation of knight moves

U64 KNIGHT_LOOKUP_TABLE[64] = {
0x0000000000020400ULL, 0x0000000000050800ULL, 0x00000000000A1100ULL, 0x0000000000142200ULL,
... and on};


U64 knights = whiteKnights;
U64 possibleMoves = enemy|empty;

//code inside the loop is incomplete btw

while(whiteKnights){

from = bit_scan_forward(knights);
targets = KNIGHT_LOOKUP_TABLE[from] & possibleMoves;
}

is this how it works?

from = bit_scan_forward(knights) finds the position of the knight; say the first knight is on c3.
is the index to KNIGHT_LOOKUP_TABLE a bit? say that the location of the knight is c3 which is bit 2 in the knight look up table, ie.,KNIGHT_LOOKUP_TABLE[2] = 0x00000000000A1100ULL

[AlvaroBegue]

Looking at the patterns in the table, it looks like the convention is that c3 is bit 18. So you'll read KNIGHT_LOOKUP_TABLE[18], which will contain the bit pattern of the squares that can be reached from a knight at c3. Then targets will be the intersection of those locations with the locations that are possible destinations for white pieces (i.e., black or empty).

Perhaps I didn't understand what part you are having trouble with...

EDIT: It could be 22 or something else instead of 18. I can't tell from that piece of code.

[acetylmine]

Yes, c3 is bit 18. Your right.



I wanted to know if c3 = bit 18 is used to index the KNIGHT_LOOKUP_TABLE[64].

So,

KNIGHT_LOOKUP_TABLE[18] = the 18th element in the array which is the bitboard with 1 bits on each square the knight can reach from c3.

[AlvaroBegue]

Yup, you got it.