docs: static long longFromBase16String(CharSequence chars, int offset) {
      Utils.checkArgument(chars.length() >= offset + LONG_BASE16, "chars too small");
      return (decodeByte(chars.charAt(offset), chars.charAt(offset + 1)) & 0xFFL) << 56
          | (decodeByte(chars.charAt(offset + 2), chars.charAt(offset + 3)) & 0xFFL) << 48
          | (decodeByte(chars.charAt(offset + 4), chars.charAt(offset + 5)) & 0xFFL) << 40
          | (decodeByte(chars.charAt(offset + 6), chars.charAt(offset + 7)) & 0xFFL) << 32
          | (decodeByte(chars.charAt(offset + 8), chars.charAt(offset + 9)) & 0xFFL) << 24
          | (decodeByte(chars.charAt(offset + 10), chars.charAt(offset + 11)) & 0xFFL) << 16
          | (decodeByte(chars.charAt(offset + 12), chars.charAt(offset + 13)) & 0xFFL) << 8
          | (decodeByte(chars.charAt(offset + 14), chars.charAt(offset + 15)) & 0xFFL);
    }