shift_subtract.c

// dividend / divisor, remainder is stored in rem.
uint128 __udivmodti4(uint128 dividend, uint128 divisor, uint128* rem) {
  if (divisor > dividend) {
    if (rem)
      *rem = dividend;
    return 0;
  }
   // Calculate the distance between most significant bits, 128 > shift >= 0.
  int shift = Distance(dividend, divisor);
  divisor <<= shift;
  quotient = 0;
  for (; shift >= 0; --shift) {
    quotient <<= 1;
    if (dividend >= divisor) {
       dividend -= divisor;
       quotient |= 1;
    }
    divisor >>= 1;
  }
  if (rem)
    *rem = dividend;
  return quotient;
}