ed: add '.' and '$' support

apps/ed/README.md

@@ -63,3 +63,7 @@ Addresses can be expressed relatively to the current line with `+` and `-`.
 lines before current line and ending 2 lines after it`.
 
 `+` alone means `+1`, `-` means `-1`.
+
+`.` means current line. It can usually be ommitted. `p` is the same as `.p`.
+
+`$` means the last line of the buffer.

apps/ed/cmd.asm

@@ -7,8 +7,7 @@
 .equ	ABSOLUTE	0
 ; handles +, - and ".". For +, easy. For -, addr is negative. For ., it's 0.
 .equ	RELATIVE	1
-.equ	BOF		2
+.equ	EOF		2
-.equ	EOF		3
 
 ; *** Variables ***
 
@@ -86,6 +85,10 @@ cmdParse:
 	jr	z, .plusOrMinus
 	cp	'-'
 	jr	z, .plusOrMinus
+	cp	'.'
+	jr	z, .dot
+	cp	'$'
+	jr	z, .eof
 	call	parseDecimalDigit
 	jr	c, .notHandled
 	; straight number
@@ -95,14 +98,22 @@ cmdParse:
 	ret	nz
 	dec	de	; from 1-based to 0-base
 	jr	.end
+.dot:
+	inc	hl	; advance cmd cursor
+	; the rest is the same as .notHandled
 .notHandled:
-	; something else. Something we don't handle. Our addr is therefore "."
+	; something else. It's probably our command. Our addr is therefore "."
 	ld	a, RELATIVE
 	ld	(ix), a
 	xor	a		; sets Z
 	ld	(ix+1), a
 	ld	(ix+2), a
 	ret
+.eof:
+	inc	hl		; advance cmd cursor
+	ld	a, EOF
+	ld	(ix), a
+	ret			; Z set during earlier CP
 .plusOrMinus:
 	push	af		; preserve that + or -
 	ld	a, RELATIVE

apps/ed/main.asm

@@ -14,8 +14,7 @@
 ; That's on a resourceful UNIX system.
 ;
 ; That doubly linked list on the z80 would use 7 bytes per line (prev, next,
-; offset, len), which is a bit much. Moreover, there's that whole "scratchpad
+; offset, len), which is a bit much.
-; being loaded in memory" thing that's a bit iffy.
 ;
 ; We sacrifice speed for memory usage by making that linked list into a simple
 ; array of pointers to line contents in scratchpad. This means that we
@@ -159,6 +158,8 @@ edResolveAddr:
 	ld	a, (ix)
 	cp	RELATIVE
 	jr	z, .relative
+	cp	EOF
+	jr	z, .eof
 	; absolute
 	ld	l, (ix+1)
 	ld	h, (ix+2)
@@ -171,6 +172,10 @@ edResolveAddr:
 	add	hl, de
 	pop	de
 	ret
+.eof:
+	ld	hl, (BUF_LINECNT)
+	dec	hl
+	ret
 
 ; Read absolute addr1 in HL and addr2 in DE. Also, check bounds and set Z if
 ; both addresses are within bounds, unset if not.