I just ran the static analysis tool "cppcheck" over the
source code of tcl8.5.15

It said many things, including

-> (warning) Array 'operatorStrings[34]' accessed at index 59, which is out of bounds. Otherwise condition 'opcode==99' is redundant.

Source code is

    const char *description, *operator = operatorStrings[opcode - INST_LOR];

    if (opcode == INST_EXPON) {
    operator = "**";
    }

Suggest move sanity check of opcode to before its use.