stdlib.cpp

#if 1 // This code is copied from https://people.cs.umu.se/isak/snippets/ltoa.c and then converted from ltoa to itoa.
/*
**  LTOA.C
**
**  Converts a integer to a string.
**
**  Copyright 1988-90 by Robert B. Stout dba MicroFirm
**
**  Released to public domain, 1991
**
**  Parameters: 1 - number to be converted
**              2 - buffer in which to build the converted string
**              3 - number base to use for conversion
**
**  Returns:  A character pointer to the converted string if
**            successful, a NULL pointer if the number base specified
**            is out of range.
*/

#include <stdlib.h>
#include <string.h>

#define BUFSIZE (sizeof(int) * 8 + 1)

char *itoa(int N, char *str, int base)
{
      int i = 2;
      int uarg;
      char *tail, *head = str, buf[BUFSIZE];

      if (36 < base || 2 > base)
            base = 10;                    /* can only use 0-9, A-Z        */
      tail = &buf[BUFSIZE - 1];           /* last character position      */
      *tail-- = '\0';

      if (10 == base && N < 0L)
      {
            *head++ = '-';
            uarg    = -N;
      }
      else  uarg = N;

      if (uarg)
      {
            for (i = 1; uarg; ++i)
            {
                  ldiv_t r;

                  r       = ldiv(uarg, base);
                  *tail-- = (char)(r.rem + ((9L < r.rem) ?
                                  ('A' - 10L) : '0'));
                  uarg    = r.quot;
            }
      }
      else  *tail-- = '0';

      memcpy(head, ++tail, i);
      return str;
}
#endif