collapseos/apps/zasm/symbol.asm
2019-05-18 18:56:27 -04:00

258 lines
6.1 KiB
NASM

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