I think it would much more straightforward to adjust the condition, i.e. when you need to reverse the specified operand order, you change JL to JNL, H to NH, NL to L, NH to H. Might be messy in the macro, but the executable part would be clean.
For the record, I wouldn't go down this road at all. Every assembler programmer has to deal with coding compare instructions, so let them handle it. sas On Fri, Aug 11, 2023 at 8:09 AM David Eisenberg <deisenbe...@optonline.net> wrote: > I’m trying to puzzle something out… I hope this question isn’t too goofy. > > I’m coding a macro to logically compare a halfword in storage to a 2-byte > unsigned constant that is calculated by the macro assembler. I want to > generate baseless code using as few instructions as possible, and I’d like > to use the fewest number of registers possible (although I have no problem > using the high-halves of any registers). My preference is to use CLHHSI to > do the compare, because no literal is required for the constant. > > However: CLHHSI requires that the constant be the second (immediate) > operand. There will be times when the macro parameters will indicate that > that comparands must be reversed (i.e., where the immediate operand must be > the first comparand), in which case I can’t use CLHHSI. > > I know that I can always code the comparands in the correct order by > loading them into the high-halves of R0 and R1, then use CLHHR. Or, of > course, I can generate a CLC with a literal. But I figured I’d ask: if I > use CLHHSI, then (if the macro determines that it’s necessary) can I modify > the resulting condition code to appear as though the original comparands > were swapped? (I.e.: CC=00 stays the same, CC=01 becomes 10, CC=10 becomes > 01.) > > So far, this is what I’ve come up with (just as an example of the macro’s > generated code): > > CLHHSI HALF,X'A24B' I like CLHHSI… no literal needed > JE DONE if the comparands are equal, don’t modify > the CC > IPM R1 > XILF R1,X'30000000' flip the bits in the CC > SPM R1 set the new CC, program mask remains > unmodified > DONE DS 0H > > Is that the best I can do? Or might there be some clever way to modify the > CC using fewer (or shorter) instructions? (Or is my entire concept > ridiculous?) > > Thanks so much, > > David >
