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collapseos/apps/zasm/parse.asm
2019-05-10 21:19:34 -04:00

134 lines
2.5 KiB
NASM

; Parse the decimal char at A and extract it's 0-9 numerical value. Put the
; result in A.
;
; On success, the carry flag is reset. On error, it is set.
parseDecimalDigit:
; First, let's see if we have an easy 0-9 case
cp '0'
ret c ; if < '0', we have a problem
sub a, '0' ; our value now is valid if it's < 10
cp 10 ; on success, C is set, which is the opposite
; of what we want
ccf ; invert C flag
ret
; Parse string at (HL) as a decimal value and return value in IX under the
; same conditions as parseNumber.
parseDecimal:
push hl
push de
push bc
ld ix, 0
.loop:
ld a, (hl)
cp 0
jr z, .end ; success!
call parseDecimalDigit
jr c, .error
; Now, let's add A to IX. First, multiply by 10.
ld d, ixh ; we need a copy of the initial copy for later
ld e, ixl
add ix, ix ; x2
add ix, ix ; x4
add ix, ix ; x8
add ix, de ; x9
add ix, de ; x10
add a, ixl
jr nc, .nocarry
inc ixh
.nocarry:
ld ixl, a
; We didn't bother checking for the C flag at each step because we
; check for overflow afterwards. If ixh < d, we overflowed
ld a, ixh
cp d
jr c, .error ; carry is set? overflow
inc hl
jr .loop
.error:
call JUMP_UNSETZ
.end:
pop bc
pop de
pop hl
ret
; Parse string at (HL) as a hexadecimal value and return value in IX under the
; same conditions as parseNumber.
parseHexadecimal:
push hl
xor a
ld ixh, a
inc hl ; get rid of "0x"
inc hl
call strlen
cp 3
jr c, .single
cp 5
jr c, .double
; too long, error
jr .error
.double:
call JUMP_PARSEHEXPAIR ; moves HL to last char of pair
jr c, .error
inc hl ; now HL is on first char of next pair
ld ixh, a
.single:
call JUMP_PARSEHEXPAIR
jr c, .error
ld ixl, a
cp a ; ensure Z
jr .end
.error:
call JUMP_UNSETZ
.end:
pop hl
ret
; Sets Z if (HL) has a '0x' or '0X' prefix.
hasHexPrefix:
ld a, (hl)
cp '0'
ret nz
push hl
inc hl
ld a, (hl)
cp 'x'
jr z, .end
cp 'X'
.end:
pop hl
ret
; Parses the string at (HL) and returns the 16-bit value in IX.
; As soon as the number doesn't fit 16-bit any more, parsing stops and the
; number is invalid. If the number is valid, Z is set, otherwise, unset.
parseNumber:
call hasHexPrefix
jr z, parseHexadecimal
jr parseDecimal
; Parse string in (HL) and return its numerical value whether its a number
; literal or a symbol. Returns value in IX.
; Sets Z if number or symbol is valid, unset otherwise.
parseNumberOrSymbol:
call parseNumber
ret z
; Not a number. Try symbol
push de
call symGetVal
jr nz, .notfound ; Z already unset
; Found! value in DE. We need it in IX
ld ixh, d
ld ixl, e
; Z already set
.notfound:
pop de
ret