rdos/debug/parse.asm

	; IN	DS:SI	remaining unparsed string
	;	CS:DI	error message
parse_error:
	push si
	mov si, .str1
	call putcs
	mov si, di
	call putcs
	mov si, .str2
	call putcs
	pop si
	call putds
	jmp crlf
.str1:	db "Not a ", 0
.str2:  db ": ", 0

	; Advance over whitespace
	; IN	DS:SI
eat_whitespace:
.loop:	lodsb
	cmp al, 0x20
	je .loop
	cmp al, 0x0A
	je .loop
	cmp al, 0x0D
	je .loop
	cmp al, 0x09
	je .loop
	dec si
	ret

	; Parse a register name
	; IN	DS:SI	string to read
	; OUT	CF set	if no match
	;	BX	register number * 2 if CF clear
eat_register:
	push si
	push es
	lodsw
	and ax, 0xDFDF
	; ES := CS
	push cs
	pop es
	mov di, rnames
	mov cx, 14
	repne scasw
	pop es
	jne .fail
	pop bx
	mov bx, di
	sub bx, (rnames+2)
	clc
	ret
.fail:	pop si
	stc
	ret
.emsg:	db "register name", 0

	; Parse hex digit
	; IN	DS:SI
	; OUT	AL
eat_hex_digit:
	push si
	lodsb
	sub al, '0'
	jc .err
	cmp al, 9
	jna .ret
	sub al, 7
	cmp al, 0xF
	ja .err
.ret:	add sp, 2
	ret
.err:	pop si
	stc
	ret
.emsg:	db "hex digit", 0

	; Parse hexadecimal byte
	; IN	DS:SI
	; OUT	DL or carry set
eat_hex_byte:
	push si
	mov cl, 4
	xor dl, dl

	call eat_hex_digit
	jc .err
	or dl, al
	shl dl, cl
	call eat_hex_digit
	jc .err
	or dl, al

	add sp, 2
	ret
.err:	pop si
	stc
	ret
.emsg:	db "hex byte", 0

	; Parse hexadecimal word
	; OUT	DX or carry set
eat_hex_word:
	push si
	xor dx, dx

	call eat_hex_byte
	jc .err
	mov dh, dl
	call eat_hex_byte
	jc .err

	add sp, 2
	ret
.err:	pop si
	stc
	ret
.emsg:	db "hex word", 0