#include <stdbool.h>
#include "string.h"
#include "stdlib.h"
#include "stddef.h"

static void strreverse( char *s )
{
	char *end = s + strlen( s ) - 1;
	
	while( s < end ) {
		// XOR swap;
		*s ^= *end;
		*end ^= *s;
		*s ^= *end;
		s++;
		end--;
	}
}
    
char *itoa( int v, char *s, int base )
{
	static char digit[] = "0123456789ABCDEF";
	bool sign = false;
	char *p = s;
	
	if( base < 2 || base > 16 ) {
		return NULL;
	}
	
	if( v < 0 ) {
		v = -v;
		sign = true;
	} 
	
	do {
		*p++ = digit[v % base];
	} while( ( v /= base ) > 0 );

	if( sign ) {
		*p++ = '-';
	}
	*p = '\0';
	
	strreverse( s );
	
	return s;
}