collapseos/apps/ed/buf.asm

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2019-07-13 14:01:20 -04:00
; buf - manage line buffer
;
; Lines in edited file aren't loaded in memory, their offsets is referenced to
; in this buffer.
;
; *** Consts ***
;
; Maximum number of lines allowed in the buffer.
.equ BUF_MAXLINES 0x800
; *** Variables ***
; Number of lines currently in the buffer
.equ BUF_LINECNT BUF_RAMSTART
; List of words pointing to scratchpad offsets
.equ BUF_LINES BUF_LINECNT+2
.equ BUF_RAMEND BUF_LINES+BUF_MAXLINES*2
; *** Code ***
bufInit:
xor a
ld (BUF_LINECNT), a
ret
; Add a new line with offset HL to the buffer
bufAddLine:
push de
push hl
ld hl, BUF_LINES
ld de, (BUF_LINECNT)
add hl, de
add hl, de ; twice, because two bytes per line
; HL now points to the specified line offset in memory
pop de ; what used to be in HL ends up in DE
; line offset popped back in HL
ld (hl), e
inc hl
ld (hl), d
; increase line count
ld hl, (BUF_LINECNT)
inc hl
ld (BUF_LINECNT), hl
; our initial HL is in DE. Before we pop DE back, let's swap these
; two so that all registers are preserved.
ex de, hl
pop de
ret
; Read line number specified in HL and loads the I/O buffer with it.
; Like ioGetLine, sets HL to line buffer pointer.
; Sets Z on success, unset if out of bounds.
bufGetLine:
push de
ld de, (BUF_LINECNT)
call cpHLDE
jr nc, .outOfBounds ; HL > (BUF_LINECNT)
ex de, hl
ld hl, BUF_LINES
add hl, de
add hl, de ; twice, because two bytes per line
; HL now points to seek offset in memory
ld e, (hl)
inc hl
ld d, (hl)
; DE has seek offset
ex de, hl
; and now HL has it. We're ready to call ioGetLine!
pop de
cp a ; ensure Z
jp ioGetLine ; preserves AF
.outOfBounds:
pop de
jp unsetZ