Small standalone stupid function to convert integer value to string, for code with zero library support

sprint_int.c

#include <stdint.h>
#include <stdio.h>
char *sprint_int_(char *out, uint64_t a, uint64_t base) {
  char itoc[] = "0123456789abcdef";
  char *orig_out = out;
  uint64_t a_ = a;
  int i = 0;
  while (a_ >= base) {
    a_ /= base;
    i++;
  }
  out[i + 1] = '\0';
  while (i >= 0) {
    out[i] = itoc[a % base];

    i--;
    a /= base;
  }
  return orig_out;
}
char *sprint_int(char *out, uint64_t a) { return sprint_int_(out, a, 10); }
char *sprint_hex(char *out, uint64_t a) { return sprint_int_(out, a, 16); }

int main() {
  char buf[100];
  printf("%s\n", sprint_int(buf, 12345));
  printf("%s\n", sprint_int(buf, 0xfffffff));
  printf("%s\n", sprint_hex(buf, 0xfffffff));
  printf("%s\n", sprint_int(buf, 0));
}