Exemplo de divisão de um número de 128 bits

128bit-division.c

#include <stdio.h>
#include <inttypes.h>

int asmdiv(uint64_t highq, uint64_t lowq, uint64_t divisor)
{
  uint64_t quotient;
  uint64_t modulous;
  
  __asm__ __volatile__ (
    "movq %[highq], %%rdx\n\t"
    "movq %[lowq],  %%rax\n\t"
    "divq %[div]\n\t"
    "movq %%rax, %[quot]\n\t"
    "movq %%rdx, %[mod]\n\t"
  
    : [quot]  "=m"  (quotient),
      [mod]   "=m"  (modulous)
    : [highq] "irm" (highq),
      [lowq]  "irm" (lowq),
      [div]   "rm"  (divisor)
  );
  
  // Mais código??
  
  printf("Quociente: %" PRIx64 "\n"
         "Resto:     %" PRIx64 "\n",
         quotient, modulous);
  
  return quotient;
}

int main(void)
{
  // https://defuse.ca/big-number-calculator.htm
  asmdiv(0x1fff, 0xffffffffffffffff, 864213455343);
  return 0;
}