How to convert short to ASCII?

Question

What is the best way(optimized by speed) to convert a short number to ascii in C (-1,5,1000 to "-1","5","1000").

I need it for embedded MCU, so the sprintf() is not an option.

Thanks

Answer 1

As @Potatoswatter succinctly comments, use standard itoa() is you have it.

As to what is fastest: best to profile candidate solutions. What works best on one platform may differ on another.

Below is an alternative implementation. Flowing is a tight recursive solution that does not need to reverse its results. It works for all int: [INT_MIN, INT_MAX] as it works with the negative side of int which is the same size or larger than the positive side.

static char *itoa10_helper(int n, char *s) {
  if (n <= -10) {
    s = itoa10_helper(n / 10, s);
  }
  *s = (char) ('0' - n % 10);
  return ++s;
}

char* itoa10(int n, char *s) {
  if (n < 0) {
    *s = '-';
    *itoa10_helper(n, s+1) = 0;
  } else {
    *itoa10_helper(-n, s) = 0;
  }
  return s;
}

#include <limits.h>
#include <stdio.h>
#define INT_MAX_SIZE (sizeof (int)*CHAR_BIT/3 + 3)

int main(void) {
  char buf[INT_MAX_SIZE];
  puts(itoa10(0, buf));
  puts(itoa10(123, buf));
  puts(itoa10(INT_MAX, buf));
  puts(itoa10(INT_MIN, buf));
  return 0;
}

---

A fast solution, that returns a pointer somewhere in the buffer provided follows:

#include <stdbool.h>

char* itoa10f(int n, char *buf) {
  char *s = buf + INT_MAX_SIZE - 1;
  *s = '\0';
  bool isnegative = n < 0;
  if (!isnegative) {
    n = -n;
  }
  do {
    *(--s) = (char) ('0' - n % 10);
  } while (n /= 10);
  if (isnegative) {
    *(--s) = '-';
  }
  return s;
}