apps/ed: first steps

apps/ed/glue.asm

@@ -0,0 +1,7 @@
+#include "user.h"
+.org	USER_CODE
+
+	jp	edMain
+
+#include "ed/main.asm"
+

apps/ed/main.asm

@@ -0,0 +1,62 @@
+; ed - line editor
+;
+; A text editor modeled after UNIX's ed, but simpler. The goal is to stay tight
+; on resources and to avoid having to implement screen management code (that is,
+; develop the machinery to have ncurses-like apps in Collapse OS).
+;
+; ed has a mechanism to avoid having to move a lot of memory around at each
+; edit. Each line is an element in an doubly-linked list and each element point
+; to an offset in the "scratchpad". The scratchpad starts with the file
+; contents and every time we change or add a line, that line goes to the end of
+; the scratch pad and linked lists are reorganized whenever lines are changed.
+; Contents itself is always appended to the scratchpad.
+;
+; 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
+; being loaded in memory" thing that's a bit iffy. We sacrifice speed for
+; memory usage.
+;
+; So here's what we do. First, we have two scratchpads. The first one is the
+; file being read itself. The second one is is memory, for modifications we
+; make to the file. When reading the file, we note the offset at which it ends.
+; All offsets under this limit refer to the first scratchpad. Other offsets
+; refer to the second.
+;
+; Then, our line list if just an array of 16-bit offsets. This means that we
+; don't have an easy access to line length and we have to move a lot of memory
+; around whenever we add or delete lines. Hopefully, "LDIR" will be our friend
+; here...
+;
+; *** Requirements ***
+; printstr
+; printcrlf
+; stdioReadC
+; stdioGetLine
+
+edMain:
+edLoop:
+	ld	hl, .prompt
+	call	printstr
+.inner:
+	call	stdioReadC
+	jr	nz, .inner	; not done? loop
+	; We're done. Process line.
+	call	printcrlf
+	call	stdioGetLine
+	call	edProcessLine
+	ret	z
+	jr	edLoop
+
+.prompt:
+	.db	":", 0
+
+; Sets Z if we need to quit
+edProcessLine:
+	call	printstr
+	ld	a, (hl)
+	cp	'q'
+	ret	z
+	call	printcrlf
+	jp	unsetZ

tools/emul/.gitignore

@@ -3,4 +3,5 @@
 /runbin/runbin
 /*/*-bin.h
 /cfsin/zasm
+/cfsin/ed
 /cfsin/user.h

tools/emul/Makefile

@@ -4,7 +4,7 @@ KERNEL = ../../kernel
 APPS = ../../apps
 ZASMBIN = zasm/zasm
 ZASMSH = ../zasm.sh
-SHELLAPPS = $(addprefix cfsin/, zasm)
+SHELLAPPS = $(addprefix cfsin/, zasm ed)
 CFSIN_CONTENTS = $(SHELLAPPS) cfsin/user.h
 
 .PHONY: all

tools/emul/shell/shell_.asm

@@ -34,6 +34,9 @@
 	jp	_blkPutC
 	jp	_blkSeek
 	jp	_blkTell
+	jp	printcrlf
+	jp	stdioReadC
+	jp	stdioGetLine
 
 #include "core.asm"
 #include "err.h"

tools/emul/shell/user.h

@@ -27,3 +27,6 @@
 .equ	_blkPutC		0x3f
 .equ	_blkSeek		0x42
 .equ	_blkTell		0x45
+.equ	printcrlf		0x48
+.equ	stdioReadC		0x4b
+.equ	stdioGetLine	0x4e