char *itoa(int value, char *str, int base) {
    char *p = str;
    char *p1, *p2;
    unsigned int uvalue = value;
    int negative = 0;

    if (base < 2 || base > 36) {
        *str = '\0';
        return str;
    }

    if (value < 0 && base == 10) {
        negative = 1;
        uvalue = -value;
    }

    // Convert to string
    do {
        int digit = uvalue % base;
        *p++ = (digit < 10) ? '0' + digit : 'a' + (digit - 10);
        uvalue /= base;
    } while (uvalue);

    if (negative)
        *p++ = '-';

    *p = '\0';

    // Reverse string
    p1 = str;
    p2 = p - 1;
    while (p1 < p2) {
        char tmp = *p1;
        *p1++ = *p2;
        *p2-- = tmp;
    }

    return str;
}