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Wed Feb 14 15:58:04 GMT 2007

bit instructions


there are a lot of bit instructions that are better handled in a
consistent way. one of the problems with the assembler is that bit set
and bit clear have different opcodes. i think it makes more sense to
handle them as one opcode + argument.

all bit instructions are polar, take another 'p' argument, so they can
be easily flipped as part of the rewriting process. the extra argument
is placed as first one, to make composition easier.

    bcf bsf -> bpf
    btfsc btfss -> btfsp
    bc bnc  -> bpc
    ...

ok, it seems to be solved with a set of pattern matching macros, and a
factored out label pusher :)


 ;; two sets of conditionals
 ((l: f b p bit?) `([bit?  ,f ,p ,p]))  ;; generic -> arguments for btfsp
 ((l: p pz?)      `([flag? bpz ,p]))    ;; flag -> conditional jump opcode
 ((l: p pc?)      `([flag? bpc ,p]))

 ;; 'cbra' recombines the pseudo ops from above into jump constructs
 ((['flag? opc p] cbra)   `([r ,opc ,(invert p) ,(make-label)]))
 ((['bit?  f b p] cbra)   `([btfsp ,(invert p) ,f ,b] [r bra ,(make-label)]))

then we have the recursive macro (if == cbra label) and the pure cat
macro (label == dup car car swap)

a lot more elegant than the previous solution. i like this pattern
matching approach.

NEXT:
* variable and other namespace stuff
* forth lexer
* parsing words
* intel hex format



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