itoa char* and std::string version

/**
 * C++ version 0.4 std::string style "itoa":
 * Contributions from Stuart Lowe, Ray-Yuan Sheu,
 * Rodrigo de Salvo Braz, Luc Gallant, John Maloney
 * and Brian Hunt
 */
std::string itoa(int value, int base) {

    std::string buf;

    // check that the base if valid
    if (base < 2 || base > 16) return buf;

    enum { kMaxDigits = 35 };
    buf.reserve( kMaxDigits ); // Pre-allocate enough space.

    int quotient = value;

    // Translating number to string with base:
    do {
        buf += "0123456789abcdef"[ std::abs( quotient % base ) ];
        quotient /= base;
    } while ( quotient );

    // Append the negative sign
    if ( value < 0) buf += '-';

    std::reverse( buf.begin(), buf.end() );
    return buf;
}


/**
 * C++ version 0.4 char* style "itoa":
 * Written by Lukás Chmela
 * Released under GPLv3.
 */
char* itoa(int value, char* result, int base) {
    // check that the base if valid
    if (base < 2 || base > 36) { *result = '\0'; return result; }

    char* ptr = result, *ptr1 = result, tmp_char;
    int tmp_value;

    do {
        tmp_value = value;
        value /= base;
        *ptr++ = "zyxwvutsrqponmlkjihgfedcba9876543210123456789abcdefghijklmnopqrstuvwxyz" [35 + (tmp_value - value * base)];
    } while ( value );

    // Apply negative sign
    if (tmp_value < 0) *ptr++ = '-';
    *ptr-- = '\0';
    while(ptr1 < ptr) {
        tmp_char = *ptr;
        *ptr--= *ptr1;
        *ptr1++ = tmp_char;
    }
    return result;
}