Code Enumeration vs. Table Entry Indexes

While designing the error handling mechanism for the INPUT command, a thought occurred related to program codes. For efficient program execution at run-time, the index of the table entry will be stored in the internal program code, not the code enumeration value.

If the code enumeration value was used, the index for the table entry (needed to get the run-time handler function pointer) would first need to be converted to an index by going through the code to index array setup during table initialization. The intention all along has been to use table entry indexes in the internal program code.

For the INPUT command's error recovery, when it is backing up execution and checking for input parse codes, it will need to convert the table entry indexes to a code before it can check if it is an input parse code. This would not efficient during program execution. Even though for the INPUT command, execution time is not critical since it is about to stop and wait for user input. A few extra program cycles won't matter much. But this problem could occur for other more critical commands.

Therefore, it is desirable if the code enumeration values were the same as the table entry indexes. One simple solution is to make sure the code enumeration values matched the table entries. Unfortunately this relies on the programmer to keep the two in sync, is very error prone and is just a general pain to begin with.

There is a better way where the code enumeration is generated automatically from the table entries using an awk script. This method would be similar to how the test_codes.h file (used by the test_ibcp.cpp source file) is generated automatically by scanning for codes in the ibcp.h file.