collapseos/apps/ed/buf.asm

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; 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
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; transform line index HL into its corresponding memory address in BUF_LINES
; array.
bufLineAddr:
push de
ex de, hl
ld hl, BUF_LINES
add hl, de
add hl, de ; twice, because two bytes per line
pop de
ret
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; 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)
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call bufLineAddr
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; 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
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; Given line indexes in HL and DE where HL < DE < CNT, move all lines between
; DE and CNT by an offset of DE-HL. Also, adjust BUF_LINECNT by DE-HL.
; WARNING: no bounds check. The only consumer of this routine already does
; bounds check.
bufDelLines:
ex de, hl
push hl ; --> lvl 1
scf \ ccf
sbc hl, de ; HL now has delcount -1
inc hl ; adjust for actual delcount
; We have the number of lines to delete in HL. We're going to move this
; to BC for a LDIR, but before we do, there's two things we need to do:
; adjust buffer line count and multiply by 2 (we move words, not bytes).
push de ; --> lvl 2
ex de, hl ; del cnt now in DE
ld hl, (BUF_LINECNT)
scf \ ccf
sbc hl, de ; HL now has adjusted line cnt
ld (BUF_LINECNT), hl
; Good! one less thing to think about. Now, let's prepare moving DE
; (delcnt) to BC. But first, we'll multiply by 2.
sla e \ rl d
push hl \ pop bc ; BC: delcount * 2
pop de ; <-- lvl 2
pop hl ; <-- lvl 1
; At this point we have higher index in HL, lower index in DE and number
; of bytes to delete in BC. It's convenient because it's rather close
; to LDIR's signature! The only thing we need to do now is to translate
; those HL and DE indexes in memory addresses, that is, multiply by 2
; and add BUF_LINES
push hl ; --> lvl 1
ex de, hl
call bufLineAddr
ex de, hl
pop hl ; <-- lvl 1
call bufLineAddr
; Both HL and DE are translated. Go!
ldir
ret