mirror of https://github.com/hsoft/collapseos.git
36 lines
970 B
NASM
36 lines
970 B
NASM
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; Parse expression in string at (HL) and returns the result in IX.
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; We expect (HL) to be disposable: we mutate it to avoid having to make a copy.
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; Sets Z on success, unset on error.
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parseExpr:
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push hl
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ld a, '+'
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call JUMP_FINDCHAR
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jr nz, .noExpr
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; Alright, we have a + and we're pointing at it. Let's advance HL and
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; recurse. But first, let's change this + into a null char. It will be
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; handy later.
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xor a
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ld (hl), a ; + changed to \0
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inc hl
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call parseExpr
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; Whether parseExpr was successful or not, we pop hl right now
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pop hl
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ret nz ; return immediately if error
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; Now we have parsed everything to the right and we have its result in
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; IX. the pop hl brought us back to the beginning of the string. Our
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; + was changed to a 0. Let's save IX somewhere and parse this.
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push de
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ld d, ixh
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ld e, ixl
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call parseNumberOrSymbol
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jr nz, .end ; error
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; Good! let's do the math!
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add ix, de
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.end:
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pop de
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ret
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.noExpr:
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pop hl
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jp parseNumberOrSymbol
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