collapseos/apps/zasm/parse.asm

; 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