98 lines
2.8 KiB
NASM
98 lines
2.8 KiB
NASM
; ed - line editor
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;
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; A text editor modeled after UNIX's ed, but simpler. The goal is to stay tight
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; on resources and to avoid having to implement screen management code (that is,
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; develop the machinery to have ncurses-like apps in Collapse OS).
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;
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; ed has a mechanism to avoid having to move a lot of memory around at each
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; edit. Each line is an element in an doubly-linked list and each element point
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; to an offset in the "scratchpad". The scratchpad starts with the file
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; contents and every time we change or add a line, that line goes to the end of
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; the scratch pad and linked lists are reorganized whenever lines are changed.
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; Contents itself is always appended to the scratchpad.
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;
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; That's on a resourceful UNIX system.
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;
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; That doubly linked list on the z80 would use 7 bytes per line (prev, next,
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; offset, len), which is a bit much. Moreover, there's that whole "scratchpad
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; being loaded in memory" thing that's a bit iffy. We sacrifice speed for
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; memory usage.
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;
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; So here's what we do. First, we have two scratchpads. The first one is the
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; file being read itself. The second one is memory, for modifications we
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; make to the file. When reading the file, we note the offset at which it ends.
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; All offsets under this limit refer to the first scratchpad. Other offsets
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; refer to the second.
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;
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; Then, our line list is just an array of 16-bit offsets. This means that we
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; don't have an easy access to line length and we have to move a lot of memory
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; around whenever we add or delete lines. Hopefully, "LDIR" will be our friend
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; here...
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;
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; *** Usage ***
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;
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; ed takes no argument. It reads from the currently selected blkdev and writes
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; to it. It repeatedly presents a prompt, waits for a command, execute the
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; command. 'q' to quit.
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;
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; Enter a number to print this line's number. For ed, we break with Collapse
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; OS's tradition of using hex representation. It would be needlessly confusing
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; when combined with commands (p, c, d, a, i). All numbers in ed are
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; represented in decimals.
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;
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; *** Requirements ***
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; BLOCKDEV_SIZE
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; blkGetC
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; blkSeek
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; printstr
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; printcrlf
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; stdioReadC
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; stdioGetLine
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; unsetZ
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edMain:
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; Dummy test. Read first line of file
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ld hl, 0
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call ioGetLine
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call printstr
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call printcrlf
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; Continue to loop
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edLoop:
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ld hl, .prompt
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call printstr
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.inner:
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call stdioReadC
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jr nz, .inner ; not done? loop
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; We're done. Process line.
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call printcrlf
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call stdioGetLine
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call .processLine
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ret z
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jr edLoop
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.prompt:
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.db ":", 0
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; Sets Z if we need to quit
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.processLine:
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ld a, (hl)
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cp 'q'
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ret z
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call parseDecimal
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jr z, .processNumber
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; nothing
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jr .processEnd
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.processNumber:
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; number is in IX
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; Because we don't have a line buffer yet, let's simply print seek
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; offsets.
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push ix \ pop hl
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call ioGetLine
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call printstr
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call printcrlf
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; continue to end
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.processEnd:
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call printcrlf
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jp unsetZ
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