/*
** return "true" if c is a hexadecimal digit
** (0-9, A-F, a-f)
*/
isxdigit(c) int c; {
  return ((c<= 'f' && c >= 'a') ||
         (c<= 'F' && c >= 'A') ||
         (c<= '9' && c >= '0'));
  }