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lib/expr: use the IX register a bit less
It's an awkward register to use and avoiding its use allows us to strip the resulting binary significantly. parseEXPR keeps the same signature though.
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@ -1,6 +1,7 @@
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; *** Requirements ***
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; findchar
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; multDEBC
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; callIXI
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;
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; *** Defines ***
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;
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@ -14,6 +15,9 @@
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; **This routine mutates (HL).**
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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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; TODO: the IX output register is a bit awkward. Nearly everywhere, I need
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; to push \ pop that thing. See if we could return the result in DE
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; instead.
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parseExpr:
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push de
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push hl
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@ -38,15 +42,16 @@ _parseExpr:
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; Operator found, string splitted. Left in (HL), right in (DE)
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call _resolveLeftAndRight
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; Whether _resolveLeftAndRight was a success, we pop our lvl 1 stack
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; out, which contains our operator row. We pop it in HL because we
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; don't need our string anymore. L-R numbers are parsed, and in DE and
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; IX.
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pop hl ; <-- lvl 1
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; out, which contains our operator row. We pop it in IX.
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; L-R numbers are parsed in HL (left) and DE (right).
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pop ix ; <-- lvl 1
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ret nz
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; Resolving left and right succeeded, proceed!
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inc hl ; point to routine pointer
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call intoHL
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jp (hl)
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inc ix ; point to routine pointer
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call callIXI
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push de \ pop ix
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cp a ; ensure Z
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ret
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; Given a string in (HL) and a separator char in A, return a splitted string,
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; that is, the same (HL) string but with the found A char replaced by a null
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@ -90,7 +95,7 @@ _findAndSplit:
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.find:
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; parse expression on the left (HL) and the right (DE) and put the results in
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; DE (left) and IX (right)
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; HL (left) and DE (right)
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_resolveLeftAndRight:
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call parseExpr
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ret nz ; return immediately if error
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@ -98,12 +103,14 @@ _resolveLeftAndRight:
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; IX. What we need to do now is the same thing on (DE) and then apply
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; the + operator. Let's save IX somewhere and parse this.
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ex de, hl ; right expr now in HL
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push ix
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pop de ; numeric left expr result in DE
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jp parseExpr
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push ix ; --> lvl 1
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call parseExpr
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pop hl ; <-- lvl 1. left
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push ix \ pop de ; right
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ret ; Z is parseExpr's result
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; Routines in here all have the same signature: they take two numbers, DE (left)
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; and IX (right), apply the operator and put the resulting number in IX.
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; and IX (right), apply the operator and put the resulting number in DE.
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; The table has 3 bytes per row: 1 byte for operator and 2 bytes for routine
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; pointer.
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exprTbl:
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@ -130,107 +137,87 @@ exprTbl:
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.db 0 ; end of table
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.plus:
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add ix, de
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cp a ; ensure Z
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add hl, de
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ex de, hl
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ret
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.minus:
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push ix
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pop hl
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ex de, hl
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scf \ ccf
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or a ; clear carry
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sbc hl, de
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push hl
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pop ix
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cp a ; ensure Z
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ex de, hl
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ret
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.mult:
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push ix \ pop bc
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call multDEBC
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push hl \ pop ix
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cp a ; ensure Z
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ld b, h
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ld c, l
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call multDEBC ; --> HL
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ex de, hl
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ret
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.div:
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; divide takes HL/DE
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push bc
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ex de, hl
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push ix \ pop de
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call divide
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push bc \ pop ix
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ld e, c
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ld d, b
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pop bc
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cp a ; ensure Z
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ret
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.mod:
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call .div
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push hl \ pop ix
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ex de, hl
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ret
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.and:
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push ix \ pop hl
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ld a, h
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and d
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ld h, a
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ld d, a
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ld a, l
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and e
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ld l, a
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push hl \ pop ix
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cp a ; ensure Z
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ld e, a
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ret
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.or:
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push ix \ pop hl
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ld a, h
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or d
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ld h, a
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ld d, a
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ld a, l
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or e
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ld l, a
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push hl \ pop ix
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cp a ; ensure Z
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ld e, a
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ret
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.xor:
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push ix \ pop hl
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ld a, h
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xor d
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ld h, a
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ld d, a
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ld a, l
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xor e
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ld l, a
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push hl \ pop ix
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cp a ; ensure Z
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ld e, a
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ret
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.rshift:
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push ix \ pop hl
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ld a, l
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ld a, e
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and 0xf
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ret z
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push bc
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ld b, a
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.rshiftLoop:
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srl d
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rr e
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srl h
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rr l
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djnz .rshiftLoop
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push de \ pop ix
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ex de, hl
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pop bc
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cp a ; ensure Z
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ret
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.lshift:
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push ix \ pop hl
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ld a, l
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ld a, e
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and 0xf
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ret z
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push bc
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ld b, a
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.lshiftLoop:
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sla e
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rl d
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sla l
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rl h
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djnz .lshiftLoop
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push de \ pop ix
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ex de, hl
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pop bc
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cp a ; ensure Z
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ret
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