efficient integer to string

char digits[] = "9876543210123456789";
int zero = 9;
template <typename T>
int IntToString(char buf[], T t)
{
  int64_t num = static_cast<int64_t>(t);
  int size = 0;
  int i = 0;
  do {
    int index = static_cast<char>(num % 10);
    num = num/10;
    buf[i++] = digits[zero+index];
    size++;
  } while (num != 0);
  if (t < 0)  {
    buf[i++] = '-';
  }
  buf[i] = '