basic: add buffer line index

CODE.md

@@ -51,6 +51,10 @@ Therefore, shadow registers should only be used in code that doesn't call
 routines or that call a routine that explicitly states that it preserves
 shadow registers.
 
+Another important note is that routines returning success with Z generally don't
+preserve AF: too complicated. But otherwise, AF is often preserved. For example,
+register fiddling routines in core try to preserve AF.
+
 ## Z for success
 
 The vast majority of routines use the Z flag to indicate success. When Z is set,
@@ -102,4 +106,12 @@ comments. Example:
     pop     af  ; <-- lvl 1
 
 I think that this should do the trick, so I'll do this consistently from now on.
+
+## String length
+
+Pretty much every routine expecting a string have no provision for a string
+that doesn't have null termination within 0xff bytes. Treat strings of such
+lengths with extra precaution and distrust proper handling of existing routines
+for those strings.
+
 [zasm]: ../apps/zasm/README.md

apps/basic/buf.asm

@@ -1,97 +1,117 @@
 ; *** Consts ***
+; maximum number of lines (line number maximum, however, is always 0xffff)
+.equ	BUF_MAXLINES	0x100
+; Size of the string pool
 .equ	BUF_POOLSIZE	0x1000
 
 ; *** Variables ***
-; A pointer to free space in the pool.
-.equ	BUF_FREE	BUF_RAMSTART
-; The line pool. Each line consists of a two bytes binary number followed by
-; a one byte length followed by the command string, which doesn't include its
-; line number (example "10 print 123" becomes "print 123"), but which is null
-; terminated. The one byte length includes null termination. For example, if
-; we have a line record starting at 0x1000 and that its length field indicates
-; 0x42, this means that the next line starts at 0x1045 (0x42+2+1).
-.equ	BUF_POOL	@+2
+; A pointer to the first free line
+.equ	BUF_LFREE	BUF_RAMSTART
+; A pointer to the first free byte in the pool
+.equ	BUF_PFREE	@+2
+; The line index. Each record consists of 4 bytes: 2 for line number,
+; 2 for pointer to string in pool. Kept in order of line numbers.
+.equ	BUF_LINES	@+2
+; The line pool. A list of null terminated strings. BUF_LINES records point
+; to those strings.
+.equ	BUF_POOL	@+BUF_MAXLINES*4
 .equ	BUF_RAMEND	@+BUF_POOLSIZE
 
 bufInit:
+	ld	hl, BUF_LINES
+	ld	(BUF_LFREE), hl
 	ld	hl, BUF_POOL
-	ld	(BUF_FREE), hl
+	ld	(BUF_PFREE), hl
 	ret
 
-; Add line at (HL) with line number DE to the pool. The string at (HL) should
+; Add line at (HL) with line number DE to the buffer. The string at (HL) should
 ; not contain the line number prefix or the whitespace between the line number
 ; and the comment.
 ; Note that an empty string is *not* an error. It will be saved as a line.
-; Don't send strings that are more than 0xfe in length. It won't work well.
 ; Z for success.
-; The only error condition that is handled is when there is not enough space
-; left in the pool to add a string of (HL)'s size. In that case, nothing will
-; be done and Z will be unset.
-;
-; DESTROYED REGISTER: DE. Too much pushpopping around to keep it. Not worth it.
+; Error conditions are:
+; * not enough space in the pool
+; * not enough space in the line index
 bufAdd:
-	push	hl	; --> lvl 1
-	push	de	; --> lvl 2
-	; First step: see if we're within the pool's bounds
+	exx			; preserve HL and DE
+	; First step: do we have index space?
+	ld	hl, (BUF_LFREE)
+	ld	de, BUF_POOL
+	or	a		; reset carry
+	sbc	hl, de
+	exx			; restore
+	; no carry? HL >= BUF_POOL, error. Z already unset
+	ret	nc
+	; Second step: see if we're within the pool's bounds
 	call	strlen
 	inc	a		; strlen doesn't include line termination
-	ld	hl, (BUF_FREE)
+	exx			; preserve HL and DE
+	ld	hl, (BUF_PFREE)
 	call	addHL
-	; add overhead (3b)
-	inc	hl \ inc hl \ inc hl
 	ld	de, BUF_RAMEND
 	sbc	hl, de
+	exx			; restore
 	; no carry? HL >= BUF_RAMEND, error. Z already unset
-	jr	nc, .error
-	; We have enough space, proceed
-	ld	hl, (BUF_FREE)
-	pop	de		; <-- lvl 2
+	ret	nc
+	; We have enough space.
+	; Third step: set line index data
+	push	de	; --> lvl 1
+	push	hl	; --> lvl 2
+	ld	hl, (BUF_LFREE)
 	ld	(hl), e
 	inc	hl
 	ld	(hl), d
 	inc	hl
-	; A has been untouched since that strlen call. Let's use it as-is.
-	ld	(hl), a
-	inc	hl	; HL now points to dest for our string.
-	ex	de, hl
-	pop	hl \ push hl	; <--> lvl 1. recall orig, but also preserve
+	ld	de, (BUF_PFREE)
+	ld	(hl), e
+	inc	hl
+	ld	(hl), d
+	inc	hl
+	ld	(BUF_LFREE), hl
+	pop	hl \ push hl	; <-- lvl 2, restore and preserve
+
+	; Fourth step: copy string to pool
+	ld	de, (BUF_PFREE)
 	call	strcpyM
-	; Copying done. Let's update the free zone marker.
-	ld	(BUF_FREE), de
-	xor	a		; set Z
-	pop	hl		; <-- lvl 1
+	ld	(BUF_PFREE), de
+	pop	hl	; <-- lvl 2
+	pop	de	; <-- lvl 1
 	ret
-.error:
+
+; Set IX to point to the beginning of the pool.
+; Z set if (IX) is a valid line, unset if the pool is empty.
+bufFirst:
+	ld	ix, BUF_LINES
+	jp	bufEOF
+
+; Given a valid line record in IX, move IX to the next line.
+; This routine doesn't check that IX is valid. Ensure IX validity before
+; calling.
+bufNext:
+	inc	ix \ inc ix \ inc ix \ inc ix
+	jp	bufEOF
+
+; Returns whether line index at IX is past the end of file, that is,
+; whether IX == (BUF_LFREE)
+; Z is set when not EOF, unset when EOF.
+bufEOF:
+	push	hl
+	push	de
+	push	ix \ pop hl
+	ld	de, (BUF_LFREE)
+	sbc	hl, de
+	jr	z, .empty
+	cp	a		; ensure Z
+.end:
 	pop	de
 	pop	hl
 	ret
+.empty:
+	call	unsetZ
+	jr	.end
 
-; Set IX to point to the first valid line we have in the pool.
-; Error if the pool is empty.
-; Z for success.
-bufFirst:
-	ld	a, (BUF_POOL+2)
-	or	a
-	jp	z, unsetZ
-	ld	ix, BUF_POOL
-	xor	a		; set Z
-	ret
-
-; Given a valid line record in IX, move IX to the next valid line.
-; This routine doesn't check that IX is valid. Ensure IX validity before
-; calling. This routine also doesn't check that the next line is within the
-; bounds of the pool because this check is done during bufAdd.
-; The only possible error is if there is no next line.
-; Z for success.
-bufNext:
-	push	de		; --> lvl 1
-	ld	d, 0
-	ld	e, (ix+2)
-	add	ix, de
-	inc	ix \ inc ix \ inc ix
-	pop	de		; <-- lvl 1
-	ld	a, (ix+2)
-	or	a
-	jp	z, unsetZ
-	xor	a		; set Z
+; Given a line index in (IX), set HL to its associated string pointer.
+bufStr:
+	ld	l, (ix+2)
+	ld	h, (ix+3)
 	ret

apps/basic/main.asm

@@ -118,8 +118,7 @@ basLIST:
 	call	printstr
 	ld	a, ' '
 	call	stdioPutC
-	push	ix \ pop hl
-	inc	hl \ inc hl \ inc hl
+	call	bufStr
 	call	printstr
 	call	printcrlf
 	call	bufNext