258 lines
6.1 KiB
NASM
258 lines
6.1 KiB
NASM
; Manages both constants and labels within a same namespace and registry.
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;
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; Local Labels
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;
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; Local labels during the "official" first pass are ignored. To register them
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; in the global registry during that pass would be wasteful in terms of memory.
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;
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; What we don instead is set up a separate register for them and have a "second
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; first pass" whenever we encounter a new context. That is, we wipe the local
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; registry, parse the code until the next global symbol (or EOF), then rewind
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; and continue second pass as usual.
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; *** Constants ***
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; Duplicate symbol in registry
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.equ SYM_ERR_DUPLICATE 0x01
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; Symbol registry buffer is full
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.equ SYM_ERR_FULLBUF 0x02
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; Maximum number of symbols we can have in the registry
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.equ SYM_MAXCOUNT 0x100
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; Size of the symbol name buffer size. This is a pool. There is no maximum name
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; length for a single symbol, just a maximum size for the whole pool.
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.equ SYM_BUFSIZE 0x1000
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; Size of the names buffer for the local context registry
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.equ SYM_LOC_BUFSIZE 0x200
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; *** Variables ***
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; Each symbol is mapped to a word value saved here.
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.equ SYM_VALUES SYM_RAMSTART
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; A list of symbol names separated by null characters. When we encounter a
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; symbol name and want to get its value, we search the name here, retrieve the
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; index of the name, then go get the value at that index in SYM_VALUES.
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.equ SYM_NAMES SYM_VALUES+SYM_MAXCOUNT*2
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; Registry for local labels. Wiped out after each context change.
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.equ SYM_LOC_VALUES SYM_NAMES+SYM_BUFSIZE
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.equ SYM_LOC_NAMES SYM_LOC_VALUES+SYM_MAXCOUNT*2
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; Pointer to the currently selected registry
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.equ SYM_CTX_NAMES SYM_LOC_NAMES+SYM_LOC_BUFSIZE
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.equ SYM_CTX_NAMESEND SYM_CTX_NAMES+2
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.equ SYM_CTX_VALUES SYM_CTX_NAMESEND+2
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.equ SYM_RAMEND SYM_CTX_VALUES+2
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; *** Code ***
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; Advance HL to the beginning of the next symbol name in SYM_NAMES except if
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; (HL) is already zero, meaning we're at the end of the chain. In this case,
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; do nothing.
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; Sets Z if it succeeded, unset it if there is no next.
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_symNext:
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xor a
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cp (hl)
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jr nz, .do ; (HL) is not zero? we can advance.
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; (HL) is zero? we're at the end of the chain.
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call unsetZ
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ret
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.do:
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; A is already 0
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call findchar ; find next null char
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; go to the char after it.
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inc hl
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cp a ; ensure Z
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ret
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symInit:
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xor a
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ld (SYM_NAMES), a
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ld (SYM_LOC_NAMES), a
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; Continue to symSelectGlobalRegistry
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symSelectGlobalRegistry:
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push af
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push hl
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ld hl, SYM_NAMES
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ld (SYM_CTX_NAMES), hl
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ld hl, SYM_NAMES+SYM_BUFSIZE
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ld (SYM_CTX_NAMESEND), hl
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ld hl, SYM_VALUES
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ld (SYM_CTX_VALUES), hl
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pop hl
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pop af
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ret
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symSelectLocalRegistry:
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push af
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push hl
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ld hl, SYM_LOC_NAMES
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ld (SYM_CTX_NAMES), hl
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ld hl, SYM_LOC_NAMES+SYM_LOC_BUFSIZE
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ld (SYM_CTX_NAMESEND), hl
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ld hl, SYM_LOC_VALUES
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ld (SYM_CTX_VALUES), hl
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ld a, h
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ld a, l
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pop hl
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pop af
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ret
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; Sets Z according to whether label in (HL) is local (starts with a dot)
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symIsLabelLocal:
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ld a, '.'
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cp (hl)
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ret
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; Place HL at the end of (SYM_CTX_NAMES) end (that is, at the point where we have two
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; consecutive null chars. We return the index of that new name in A.
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; If we're within bounds, Z is set, otherwise unset.
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symNamesEnd:
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push bc
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push de
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ld b, 0
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ld hl, (SYM_CTX_NAMES)
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ld de, (SYM_CTX_NAMESEND)
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.loop:
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call _symNext
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jr nz, .success ; We've reached the end of the chain.
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; Are we out of bounds?
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call cpHLDE
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jr nc, .outOfBounds ; HL >= DE
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djnz .loop
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; exhausted djnz? out of bounds
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.outOfBounds:
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call unsetZ
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jr .end
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.success:
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; Our index is 0 - B (if B is, for example 0xfd, A is 0x3)
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xor a
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sub b
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cp a ; ensure Z
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.end:
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pop de
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pop bc
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ret
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; Register label in (HL) (minus the ending ":") into the symbol registry and
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; set its value in that registry to DE.
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; If successful, Z is set and A is the symbol index. Otherwise, Z is unset and
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; A is an error code (SYM_ERR_*).
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symRegister:
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push hl
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push bc
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push de
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; First, let's get our strlen
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call strlen
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ld c, a ; save that strlen for later
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ex de, hl ; symbol to add is now in DE
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call symNamesEnd
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jr nz, .error
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; A is our index. Save it
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ex af, af'
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; Is our new name going to make us go out of bounds?
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push hl
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push de
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ld de, (SYM_CTX_NAMESEND)
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ld a, c
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call addHL
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call cpHLDE
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pop de
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pop hl
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jr nc, .error ; HL >= DE
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; HL point to where we want to add the string
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ex de, hl ; symbol to add in HL, dest in DE
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; Copy HL into DE until we reach null char
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; C already have our strlen (minus null char). Let's prepare BC for
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; a LDIR.
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inc c ; include null char
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ld b, 0
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ldir ; copy C chars from HL to DE
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; We need to add a second null char to indicate the end of the name
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; list. DE is already correctly placed.
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xor a
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ld (de), a
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; I'd say we're pretty good just about now. What we need to do is to
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; save the value in our original DE that is just on top of the stack
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; into the proper index in (SYM_CTX_VALUES). Our index, remember, is
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; currently in A'.
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ex af, af'
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pop de
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push de ; push it right back to avoid stack imbalance
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ld hl, (SYM_CTX_VALUES)
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call addHL
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call addHL ; twice because our values are words
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; Everything is set! DE is our value HL points to the proper index in
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; (SYM_CTX_VALUES). Let's just write it (little endian).
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ld (hl), e
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inc hl
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ld (hl), d
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.error:
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; Z already unset
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pop de
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pop bc
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pop hl
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ret
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; Select global or local registry according to label name in (HL)
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symSelect:
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call symIsLabelLocal
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jp z, symSelectLocalRegistry
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jp symSelectGlobalRegistry
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; Find name (HL) in (SYM_CTX_NAMES) and returns matching index in A.
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; If we find something, Z is set, otherwise unset.
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symFind:
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push hl
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push bc
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push de
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ex de, hl ; it's easier if HL is haystack and DE is
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; needle.
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ld b, 0
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ld hl, (SYM_CTX_NAMES)
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.loop:
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call strcmp
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jr z, .match
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; ok, next!
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call _symNext
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jr nz, .nomatch ; end of the chain, nothing found
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djnz .loop
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; exhausted djnz? no match
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.nomatch:
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call unsetZ
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jr .end
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.match:
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; Our index is 0 - B (if B is, for example 0xfd, A is 0x3)
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xor a
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sub b
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cp a ; ensure Z
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.end:
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pop de
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pop bc
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pop hl
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ret
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; Return value associated with symbol index A into DE
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symGetVal:
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; our index is in A. Let's fetch the proper value
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push hl
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ld hl, (SYM_CTX_VALUES)
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call addHL
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call addHL ; twice because our values are words
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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
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ret
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