fast　(maybe) itoa without division

gistfile1.txt

#include <stdio.h>

char *itoa(short n, char *out) {
  char *orgout = out;
  static short tab[] = {1000, 100, 10, 1};
  int cn;
  
  cn = 0;
  while (n >= 10000) {
    cn++;
    n -= 10000;
  }
  if (cn > 0) {
    *out++ = (cn + '0');
  }

  for (int i = 0; i < 4; i++) {
    short num = tab[i];
    short num5xx = (num << 2) + num; 
    cn = 0;
    if (n >= num5xx) {
      cn += 5;
      n -= num5xx;
    }

    short num3xx = (num << 1) + num;
    if (n >= num3xx) {
      cn += 3;
      n -= num3xx;
    }

    if (n >= num) {
      cn++;
      n -= num;
    }
    if (n >= num) {
      cn++;
      n -= num;
    }
    if (cn > 0 || out != orgout) {
      *out++ = (cn + '0');
    }
  }

  if (out == orgout) {
    *out++ = '0';
  }
  *out = '\0';

  return orgout;
}

void main(void) {
  char buf[6];
  puts(itoa(32767, buf));
  puts(itoa(32766, buf));
  puts(itoa(10001, buf));
  puts(itoa(10000, buf));
  puts(itoa(12345, buf));
  puts(itoa(5678, buf));
  puts(itoa(9012, buf));
  puts(itoa(9999, buf));
  puts(itoa(0, buf));
}