[Oberon] Numeric CASE vs IF THEN ELSE Performance

Andreas Pirklbauer andreas_pirklbauer at yahoo.com
Sun Jun 10 12:04:39 CEST 2018

  > If you compile this example on your implementation you
  > will be able to compare the code generated by each.
  > If you look at the disassembler listing you will see that
  > another CASE benefit (particularly useful in embedded
  > systems) is that it uses significantly less code space
  > than IF THEN ELSE as long as the selections are not
  > too sparse. The total code generated for each version
  > of the Soundex procedures is:
  > IF-THEN-ELSE: 420 Bytes
  > CASE: 240 Bytes 

Thx. That’s a helpful hint. Unfortunately my compiler (so far) only
implements the "jump-table technique", so it does not fare well (in
terms of code-space requirements) in cases where the sparseness
of values in the case-label range is high, as outlined in [1].

A proper comparison with your technique (using a modified BR
instruction) would probably have to implement some of the other
techniques suggested in [1], such as the search tree (effectively
leading to a modern version of the paper in the process..).

But your numbers are appealing indeed!


[1]  http://bernd-oppolzer.de/CaseStmts.pdf
("The implementation of Case Statements in Pascal”)

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