collapseos/apps/zasm/symbol.asm
2019-05-13 20:23:10 -04:00

249 lines
6.1 KiB
NASM

; Manages both constants and labels within a same namespace and registry.
;
; About local labels: They are treated as regular labels except they start with
; a dot (example: ".foo"). Because labels are registered in order and because
; constants are registered in the second pass, they end up at the end of the
; symbol list and don't mix with labels. Therefore, we easily iterate through
; local labels of a context by starting from that context's index and iterating
; as long as symbol name start with a '.'
; *** 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
; *** 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)
; Index of the symbol found during the last symSetContext call
.equ SYM_CONTEXT_IDX SYM_NAMES+SYM_BUFSIZE
; Pointer, in the SYM_NAMES buffer, of the string found during the last
; symSetContext call
.equ SYM_CONTEXT_PTR SYM_CONTEXT_IDX+1
.equ SYM_RAMEND SYM_CONTEXT_PTR+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 JUMP_UNSETZ
ret
.do:
; A is already 0
call JUMP_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_CONTEXT_IDX), a
ld hl, SYM_CONTEXT_PTR
ld (SYM_CONTEXT_PTR), hl
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_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_NAMES
ld de, SYM_NAMES+SYM_BUFSIZE
.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 JUMP_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 hl, de ; 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_NAMES+SYM_BUFSIZE
ld a, c
call JUMP_ADDHL
call cpHLDE
pop de
pop hl
jr nc, .error ; HL >= DE
; HL point to where we want to add the string
ex hl, de ; 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
; 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_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_VALUES
call JUMP_ADDHL
call JUMP_ADDHL ; twice because our values are words
; Everything is set! DE is our value HL points to the proper index in
; SYM_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
; Find name (HL) in SYM_NAMES and returns matching index in A.
; If we find something, Z is set, otherwise unset.
symFind:
push hl
call _symFind
pop hl
ret
; Same as symFind, but leaks HL
_symFind:
push bc
push de
; First, what's our strlen?
call strlen
ld c, a ; let's save that
call symIsLabelLocal ; save Z for after the 3 next lines, which
; doesn't touch flags. We need to call this now
; before we lose HL.
ex hl, de ; it's easier if HL is haystack and DE is
; needle.
ld b, 0
ld hl, SYM_NAMES
jr nz, .loop ; not local? jump right to loop
; local? then we need to adjust B and HL
ld hl, (SYM_CONTEXT_PTR)
ld a, (SYM_CONTEXT_IDX)
ld b, a
xor a
sub b
ld b, a
.loop:
ld a, c ; recall strlen
call JUMP_STRNCMP
jr z, .match
; ok, next!
call _symNext
jr nz, .nomatch ; end of the chain, nothing found
djnz .loop
; exhausted djnz? no match
.nomatch:
call JUMP_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
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_VALUES
call JUMP_ADDHL
call JUMP_ADDHL ; twice because our values are words
ld e, (hl)
inc hl
ld d, (hl)
pop hl
ret
; Find symbol name (HL) in the symbol list and set SYM_CONTEXT_* accordingly.
; When symFind will be called with a symbol name starting with a '.', the search
; will begin at that context instead of the beginning of the register.
; Sets Z if symbol is found, unsets it if not.
symSetContext:
push hl
call _symFind
jr nz, .end ; Z already unset
ld (SYM_CONTEXT_IDX), a
ld (SYM_CONTEXT_PTR), hl
; Z already set
.end:
pop hl
ret