attacks.c

/* This is what I do at the moment for a knight. */

void GenKnightBitlist(struct Board * b, int tmp, int from)
{
    int i, j, col;

    i = from;
    col = FILE (i);
    j = i - 6;
    if (j >= 0 && col < 6) {
        b->bitlist[j] ^= tmp;
    }
    j = i - 10;
    if (j >= 0 && col > 1) {
        b->bitlist[j] ^= tmp;
    }
    j = i - 15;
    if (j >= 0 && col < 7) {
        b->bitlist[j] ^= tmp;
    }
    j = i - 17;
    if (j >= 0 && col > 0) {
        b->bitlist[j] ^= tmp;
    }
    j = i + 6;
    if (j < 64 && col > 1) {
        b->bitlist[j] ^= tmp;
    }
    j = i + 10;
    if (j < 64 && col < 6) {
        b->bitlist[j] ^= tmp;
    }
    j = i + 15;
    if (j < 64 && col > 0) {
        b->bitlist[j] ^= tmp;
    }
    j = i + 17;
    if (j < 64 && col < 7) {
        b->bitlist[j] ^= tmp;
    }
}

/* This is what you're suggesting. */
char KnightArray[64][32][8]; /* 16KB */

void InitKnightArray()
{
    int i, j, col, tmp;

    for (i = 0; i < 64; i++) {
        for (tmp = 0; tmp < 32; tmp++) { 
            col = FILE (i);
            j = i - 6;
            if (j >= 0 && col < 6) {
                KnightArray[i][tmp][0] = j;
            } else {
                KnightArray[i][tmp][0] = INVALID;
            }
            /* Ad nauseam */
        }
    }
}

void GenKnightBitlist(struct Board * b, int tmp, int from)
{
    int dest;
    for (int i = 0; i < 8; i++) {
        if ((dest = KnightArray[from][tmp][i]) != INVALID) {
            b->bitlist[dest] ^= 1 << tmp;
        }
    }
}

/* Which will likely not be faster. */