optimizing_64_bit.cpp

#if defined(__x86_64__)
inline uint64_t Divide128Div64To64(uint64_t high, uint64_t low,
                                   uint64_t divisor, uint64_t* remainder) {
  uint64_t result;
  __asm__("divq %[v]"
          : "=a"(result), "=d"(*remainder) // Output parametrs, =a for rax, =d for rdx, [v] is an
                                           // alias for divisor, input paramters "a" and "d" for low and high.
          : [v] "r"(divisor), "a"(low), "d"(high));
  return result;
}
#endif

tu_int __udivmodti4(tu_int dividend, tu_int divisor, tu_int* remainder) {
...

#if defined(__x86_64__)
  if (divisor.high == 0 && dividend.high < divisor) {
    remainder->high = 0;
    uint64_t quotient =
        Divide128Div64To64(dividend.high, dividend.low,
                           divisor.low, &remainder->low);
    return quotient;
  }
#endif
...
}