typedef unsigned int I;
I mul (I ier, I icand){
  I q = 1, ac = 0;
  while(q <= ier) q <<= 1; // ier might be too big for this.
  while(q >>= 1) {ac <<= 1; if (q & ier) ac += icand;}
  return ac;}

#include <stdio.h>
int main(){
  {int j = 55; while(j--) {int k=42; while(k--) if(j*k != mul(j, k))
  printf("i = %d, j = %d, mul(i, j) = %d\n", j, k, mul(j, k));}}
  return 0;}