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105 lines
2.0 KiB
NASM
105 lines
2.0 KiB
NASM
; *** Variables ***
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; A list of words for each member of the A-Z range.
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.equ VAR_TBL VAR_RAMSTART
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.equ VAR_RAMEND @+52
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; *** Code ***
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varInit:
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ld b, VAR_RAMEND-VAR_RAMSTART
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ld hl, VAR_RAMSTART
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xor a
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.loop:
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ld (hl), a
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inc hl
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djnz .loop
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ret
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; Check if A is a valid variable letter (a-z or A-Z). If it is, set A to a
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; valid VAR_TBL index and set Z. Otherwise, unset Z (and A is destroyed)
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varChk:
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call upcase
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sub 'A'
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ret c ; Z unset
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cp 27 ; 'Z' + 1
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jr c, .isVar
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; A > 'Z'
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dec a ; unset Z
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ret
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.isVar:
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cp a ; set Z
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ret
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; Try to interpret line at (HL) and see if it's a variable assignment. If it
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; is, proceed with the assignment and set Z. Otherwise, NZ.
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varTryAssign:
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inc hl
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ld a, (hl)
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dec hl
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cp '='
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ret nz
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ld a, (hl)
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call varChk
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ret nz
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; We have a variable! Its table index is currently in A.
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push ix ; --> lvl 1
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push hl ; --> lvl 2
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push de ; --> lvl 3
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push af ; --> lvl 4. save for later
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; Let's put that expression to read in scratchpad
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inc hl \ inc hl
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ld de, SCRATCHPAD
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call rdWord
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ex de, hl
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; Now, evaluate that expression now in (HL)
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call parseExpr ; --> number in DE
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jr nz, .exprErr
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pop af ; <-- lvl 4
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call varAssign
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xor a ; ensure Z
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.end:
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pop de ; <-- lvl 3
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pop hl ; <-- lvl 2
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pop ix ; <-- lvl 1
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ret
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.exprErr:
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pop af ; <-- lvl 4
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jr .end
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; Given a variable **index** in A (call varChk to transform) and a value in
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; DE, assign that value in the proper cell in VAR_TBL.
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; No checks are made.
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varAssign:
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push hl
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add a, a ; * 2 because each element is a word
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ld hl, VAR_TBL
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call addHL
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; HL placed, write number
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ld (hl), e
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inc hl
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ld (hl), d
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pop hl
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ret
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; Check if value at (HL) is a variable. If yes, returns its associated value.
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; Otherwise, jump to parseLiteral.
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parseLiteralOrVar:
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call isLiteralPrefix
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jp z, parseLiteral
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; not a literal, try var
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ld a, (hl)
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call varChk
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ret nz
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; It's a variable, resolve!
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add a, a ; * 2 because each element is a word
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push hl ; --> lvl 1
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ld hl, VAR_TBL
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call addHL
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ld e, (hl)
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inc hl
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ld d, (hl)
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pop hl ; <-- lvl 1
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inc hl ; point to char after variable
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cp a ; ensure Z
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ret
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