(Pawn) doAdd, doMul. Bits aritmetics operators

/*
*  Copyright (c) 2013
*  Bruno da Silva
*  Bits Mul, Add
*/
stock doMul(x, y) {

    new p;

    for ( p = 0 ; x ;  x >>= 1 ,  y <<= 1) {

        if (x & 1) {

            for( ; y ; ) {
                p = p ^ y;
                y = (p ^ y) & y;
                y = y << 1;
            }
        }
   }

   return p;
}


stock doAdd(a , b) {

    for( ; b ; ) {
        a ^= b;
        b = (a ^ b) & b;
        b <<=  1;
    }

    return a;
}

main() {

    printf("4 x 6 = %d", doMul(4,6));  // 24
    printf("4 + 6 = %d", doAdd(4,6)); // 10

}