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LOAD: do not mistake a line number for the end of file marker #6

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LOAD: do not mistake a line number for the end of file marker #6

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52 changes: 50 additions & 2 deletions src/cpmio.asm
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,7 @@ FCBRC .equ FCB+15 ; file's record count (0 to 128)
FCBCR .equ FCB+32 ; current (next) record
FCBLN .equ FCB+33 ; FCB length
FTYPE .db "TBA" ; tasty basic file type
lastnum .dw 0 ; last line number the loader read

haschar:
push bc
Expand Down Expand Up @@ -98,16 +99,63 @@ lo1:
ld hl,(textunfilled)
lo2:
ld a,(de) ; get char from buffer
cp 1ah ; is it EOF?
jr z,lo3 ; yes, all done
ld (hl),a ; copy char to text area
inc hl ; and update pointers
inc de
ld (textunfilled),hl
dec b ; end of record?
jr z,lo1 ; yes, so try next record
jr lo2 ; no, copy next char
; The whole file is in memory now. Walk the lines to find where the program
; ends: only at a line's first byte can 1ah be the end of file marker, and
; even there it is only the marker when the two bytes do not read as a line
; number after the one before it. Line numbers ascend; what follows the
; marker does not.
lo3:
ld de,(textunfilled) ; de -> past the last byte read
ld hl,0
ld (lastnum),hl ; no line read yet
ld hl,textbegin
lo4:
push hl ; hl -> a line's first byte
or a
sbc hl,de
pop hl
jr nc,lo7 ; nothing left: no marker in the file
ld a,(hl)
cp EOF
jr nz,lo5 ; not the marker, so a line: read it
push hl ; the marker, where a line could begin:
ld a,(hl) ; does it read as the next number?
inc hl
ld h,(hl)
ld l,a
ld bc,(lastnum)
or a
sbc hl,bc
pop hl
jr z,lo7 ; not greater than the last: the end
jr c,lo7
lo5:
ld a,(hl) ; this line's number is the one the
ld (lastnum),a ; next one has to beat
inc hl
ld a,(hl)
ld (lastnum+1),a
inc hl
lo6:
push hl
or a
sbc hl,de
pop hl
jr nc,lo7 ; ran off the end mid line
ld a,(hl)
inc hl
cp cr ; a line ends at its first cr
jr nz,lo6
jr lo4
lo7:
ld (textunfilled),hl
jp rstart
save:
call fname ; ** save **
Expand Down