Topic       : The GFA-Basic Compendium
Author      : GFA Systemtechnik GmbH
Version     : GFABasic.HYP v2.98 (12/31/2023)
Subject     : Documentation/Programming
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View Ref-FileThe $S> and $S< options determine the optimizing criterion for the SELECT-CASE
instructions. $S> leads to optimization by execution time, $S< according to
program length.

You have seen in the last section how, at the end of the program blocks after
the CASE and the DEFAULT instructions, bra.s branches into the line following
ENDSELECT. However, if the program blocks are longer than in the last section,
where they only contained an addq, bra must be used instead of bra.s.

The space required for the specification of the jump distance is larger with
bra than with bra.s. The $S< option can be used to save this space. It results
in the bra instruction at the end of a CASE block to be directed to the bra
instruction of the next block (after the next CASE or DEFAULT), as long as the
jump distance is small enough.

This could result in a chain of short branch jumps which finally ends behind
ENDSELECT. This chain of jumps from bra.s to bra.s may again be altered by the
compiler at a later stage of optimization.

This not altogether straight forward problem is clarified by the following
listing:

              move.l  -$8000(a5),d0
              bra     L1
    _CASE_1:  addq.l  #$1,-$8000(a5)
              bra.s   L0
    _CASE_2:  addq.l  #$1,-$8000(a5)
    L0:       bra     L2
    _DEFAULT: addq.l  #$1,-$8000(a5)
              ...
              Many instructions
              ...
    L2:       bra.s   _ENDSEL
    L1:       cmpi.w  #$1,d0 ;CASE evaluation
              beq     _CASE_1
              cmpi.w  #$2,d0
              beq     _CASE_2
              bra     _DEFAULT
    _ENDSEL   addq.l  #$1,-$8000(a5)

The crucial point here is the line bra.s L0. This branch should really go to
behind ENDSELECT. But the distance would be too far for a bra.s because of the
many instructions in the DEFAULT block. Hence the branch is to the bra command
in the next CASE program block.

While this method is executed more slowly, it requires less space than the code
generated with $S>, which does without such jumps.

Memo: $S> is the default.