# Dev notes — 2023-08-12

## Call stack

Brainstorming/sketching around subroutines with a return stack...

    ; need an instruction for IP → A i guess?
    ; ideally…
    ; but a jump table would work
    ; put that at beginning of the code
    ; then store numbers for subroutine labels in a designated memory slot

    lda $1
    sto $19 ; contains ID # for the next fn to jump to

    @jump_table
    hop $1
      jmp @jt2
    jmp @example_computation
    @jt2
    hop $2
      ; jmp @jt3
      nop
    ; etc …
    jmp @end

    @example_computation
    lda 5
    sto $20
    lda 3
    sto $21
    ; $19 still has the # for this routine
    ; but let’s pretend it doesn’t and demonstrate updating it
    lda $1
    sto $19
    jmp @greater?

    ; call with numbers to test in $20 and $21
    ; result is stored in acc
    @greater?
    ; lda ($20)
    ; sub ($21)
    ; todo…
    ; wouldn’t it be great to have a “hop if neg” op…
    ; do we have to just subtract numbers until we get 0?

    ; no!
    ; here’s an approach that’s at least better than that
    lda ($21)
    sto $22 ; stash
    @loop
    lda ($21)
    sub $1
    sto $22 ; stash
    sub ($20)
    hop $0
      jmp @loop
    sto $1
    jmp $jmp_table
    ; ok this isn’t quite it… we also need to chexk if we hit 0 by just deceementinf and if so retuen 0

    jmp @jump_table