/* Exercise compiler’s division-by-a-constant optimizations.

GCC for amd64 does fine, while avr-gcc 4.9.2 punts to __divmodhi4:

    avr-gcc -g -c -mmcu=atmega328p -O5 -Wa,-adlhns=div10.lst div10.c

See <https://homepage.divms.uiowa.edu/~jones/bcd/divide.html> for some
other things it could maybe do instead.

 */

static int inner_utoa(int n, char *d, char rv)
{
  *d++ = '0' + n % 10;
  n /= 10;
  return n ? inner_utoa(n, d, rv + 1) : rv + 1;
}

static void reverse(char *s, char len)
{
  char *t = s + len;
  while (--t > s) {
    char tmp = *s;
    *s = *t;
    *t = tmp;
    s++;
  }
}

void outer_utoa(int n, char *d)
{
  char len = inner_utoa(n, d, 0);
  reverse(d, len);
  d[(int)len] = '\0';
}

#ifdef __linux__
#include <stdlib.h>
#include <stdio.h>
int main(int argc, char **argv)
{
  char buf[99];
  int n = atoi(argv[1]);
  outer_utoa(n, buf);
  printf("%d == \"%s\"\n", n, buf);
  return 0;
}
#endif