basic: keep line index ordered and line numbers unique

apps/basic/buf.asm

@@ -33,16 +33,7 @@ bufInit:
 ; * not enough space in the pool
 ; * not enough space in the line index
 bufAdd:
-	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
+	; Check whether we have enough pool space. This is done in all cases.
 	call	strlen
 	inc	a		; strlen doesn't include line termination
 	exx			; preserve HL and DE
@@ -53,31 +44,81 @@ bufAdd:
 	exx			; restore
 	; no carry? HL >= BUF_RAMEND, error. Z already unset
 	ret	nc
-	; We have enough space.
-	; Third step: set line index data
-	push	de	; --> lvl 1
-	push	hl	; --> lvl 2
+
+	; Check the kind of operation we make: add, insert or replace?
+	call	bufFind
+	jr	z, .replace	; exact match, replace
+	call	c, .insert	; near match, insert
+
+	; do we have enough index space?
+	exx			; preserve HL and DE
 	ld	hl, (BUF_LFREE)
-	ld	(hl), e
-	inc	hl
-	ld	(hl), d
-	inc	hl
+	ld	de, BUF_POOL-4
+	or	a		; reset carry
+	sbc	hl, de
+	exx			; restore
+	; no carry? HL >= BUF_POOL, error. Z already unset
+	ret	nc
+
+	; We have enough space.
+	; set line index data
+	push	de	; --> lvl 1
+	ld	(ix), e
+	ld	(ix+1), d
 	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
+	ld	(ix+2), e
+	ld	(ix+3), d
+
+	; Increase line index size
+	ld	de, (BUF_LFREE)
+	inc	de \ inc de \ inc de \ inc de
+	ld	(BUF_LFREE), de
 
 	; Fourth step: copy string to pool
 	ld	de, (BUF_PFREE)
 	call	strcpyM
 	ld	(BUF_PFREE), de
-	pop	hl	; <-- lvl 2
 	pop	de	; <-- lvl 1
 	ret
 
+; No need to add a new line, just replace the current one.
+.replace:
+	ld	(ix), e
+	ld	(ix+1), d
+	push	de
+	ld	de, (BUF_PFREE)
+	ld	(ix+2), e
+	ld	(ix+3), d
+	call	strcpyM
+	ld	(BUF_PFREE), de
+	pop	de
+	ret
+
+; An insert is exactly like an add, except that lines following insertion point
+; first.
+.insert:
+	push	hl
+	push	de
+	push	bc
+	; We want a LDDR that moves from (BUF_LFREE)-1 to (BUF_LFREE)+3
+	; for a count of (BUF_LFREE)-BUF_LINES
+	ld	hl, (BUF_LFREE)
+	ld	de, BUF_LINES
+	or	a		; clear carry
+	sbc	hl, de
+	ld	b, h
+	ld	c, l
+	ld	hl, (BUF_LFREE)
+	ld	d, h
+	ld	e, l
+	dec	hl
+	inc	de \ inc de \ inc de
+	lddr
+	pop	bc
+	pop	de
+	pop	hl
+	ret
+
 ; 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:
@@ -98,6 +139,7 @@ bufEOF:
 	push	hl
 	push	de
 	push	ix \ pop hl
+	or	a		; clear carry
 	ld	de, (BUF_LFREE)
 	sbc	hl, de
 	jr	z, .empty
@@ -115,3 +157,25 @@ bufStr:
 	ld	l, (ix+2)
 	ld	h, (ix+3)
 	ret
+
+; Browse lines looking for number DE. Set IX to point to one of these :
+; 1 - an exact match
+; 2 - the first found line to have a higher line number
+; 3 - EOF
+; Set Z on an exact match, C on a near match, NZ and NC on EOF.
+bufFind:
+	call	bufFirst
+	ret	nz
+.loop:
+	ld	a, d
+	cp	(ix+1)
+	ret	c	; D < (IX+1), situation 2
+	jr	nz, .next
+	ld	a, e
+	cp	(ix)
+	ret	c	; E < (IX), situation 2
+	ret	z	; exact match!
+.next:
+	call	bufNext
+	ret	nz
+	jr	.loop