cc65/libsrc/atari/lseek.s

;
; Christian Groessler, May 2002
;
; this file provides the lseek() function
;
; off_t __fastcall__ lseek(int fd, off_t offset, int whence);
;


 	.export		_lseek
	.import		incsp6,__oserror
	.import		__inviocb,ldax0sp,ldaxysp,fdtoiocb
	.import		__seterrno,__dos_type
	.import		fd_table
	.importzp	sreg,ptr1,ptr2,ptr3,ptr4
	.importzp	tmp1,tmp2,tmp3
	.include	"atari.inc"
	.include	"errno.inc"
	.include	"fd.inc"

; seeking not supported, return -1 and ENOSYS errno value
no_supp:jsr	incsp6
	lda	#<ENOSYS
	ldx	#>ENOSYS
	jsr	__seterrno
	ldx	#0
	stx	__oserror
	dex
	txa
	sta	sreg
	sta	sreg+1
	rts

parmerr:
iocberr:jsr	incsp6
	ldx	#255
	stx	sreg
	stx	sreg+1
	jmp	__inviocb


; lseek() entry point

.proc	_lseek

	cpx	#0		; sanity check whence parameter
	bne	parmerr
	cmp	#3		; valid values are 0..2
	bcs	parmerr
	sta	tmp1		; remember whence

	ldy	#5
	jsr	ldaxysp		; get fd
	jsr	fdtoiocb	; convert to iocb in A, fd_table index in X
	bmi	iocberr
	sta	tmp3		; remember iocb

	jsr	chk_supp	; check, whether seeking is supported by DOS/Disk
	bcc	no_supp

	ldx	tmp1		; whence
	beq	cur
	dex
	beq	end

; SEEK_SET
	dex
	stx	ptr3
	stx	ptr3+1
	stx	ptr4
	stx	ptr4+1
	beq	cont

; SEEK_CUR
cur:	ldx	tmp3
	lda	#38		; NOTE
	sta	ICCOM,x
	jsr	CIOV		; read it
	bmi	xxerr
l01:	lda	ICAX3,x		; low byte of position
	sta	ptr3
	lda	ICAX4,x		; med byte of position
	sta	ptr3+1
	lda	ICAX5,x		; high byte of position
	sta	ptr4
	lda	#0
	sta	ptr4+1
	beq	cont

; SEEK_END
end:	ldx	tmp3
	lda	#39		; get file size
	sta	ICCOM,x
	jsr	CIOV
	bpl	l01

; error returned from CIO
xxerr:	sty	__oserror
	bmi	iocberr

; check for offset 0, SEEK_CUR (get current position)
cont:	ldy	#3
	jsr	ldaxysp		; get upper word
	sta	ptr1
	stx	ptr1+1
	jsr	ldax0sp		; get lower word
	stx	tmp2
	ora	tmp2
	ora	ptr1
	ora	ptr1+1
	bne	seek
	lda	tmp1		; whence (0 = SEEK_CUR)
	bne	seek

; offset 0, SEEK_CUR: return current fp
ret:	jsr	incsp6

	lda	ptr4+1
	sta	sreg+1
	lda	ptr4
	sta	sreg
	ldx	ptr3+1
	lda	ptr3

.if 0
	; return exactly the position DOS has
	ldx	tmp3
	lda	#38		; NOTE
	sta	ICCOM,x
	jsr	CIOV		; read it
	bmi	xxerr
	lda	#0
	sta	sreg+1
	lda	ICAX5,x		; high byte of position
	sta	sreg
	lda	ICAX3,x		; low byte of position
	pha
	lda	ICAX4,x		; med byte of position
	tax
	pla
.endif

	rts

parmerr1: jmp	parmerr

; we have to call POINT
seek:	jsr	ldax0sp		; get lower word of new offset
	clc
	adc	ptr3
	sta	ptr3
	txa
	adc	ptr3+1
	sta	ptr3+1
	lda	ptr1
	adc	ptr4
	sta	ptr4
	lda	ptr1+1
	adc	ptr4+1
	sta	ptr4+1
	bne	parmerr1	; resulting value too large

	ldx	tmp3		; IOCB
	lda	ptr3
	sta	ICAX3,x
	lda	ptr3+1
	sta	ICAX4,x
	lda	ptr4
	sta	ICAX5,x
	lda	#37		;POINT
	sta	ICCOM,x
	jsr	CIOV
	bpl	ret
	bmi	xxerr

.endproc

; check, whether seeking is supported
; tmp3:		iocb
; X:		index into fd_table
;
; On non-SpartaDOS, seeking is not supported.
; We check, whether CIO function 39 (get file size) returns OK.
; If yes, NOTE and POINT work with real file offset.
; If not, NOTE and POINT work with the standard ScNum/Offset values.
; We remember a successful check in fd_table.ft_flag, bit 3.

chk_supp:
	lda	fd_table+ft_flag,x
	and	#8
	bne	supp

; do the test
	lda	__dos_type
	cmp	#SPARTADOS
	bne	ns1
	txa
	pha
	lda	DOS+1		; get SpartaDOS version
	cmp	#$40
	bcs	supp1		; SD-X (ver 4.xx) supports seeking on all disks
	ldx	tmp3		; iocb to use
	lda	#39		; get file size
	sta	ICCOM,x
	jsr	CIOV
	bmi	notsupp		; error code ? should be 168 (invalid command)

; seeking is supported on this DOS/Disk combination

supp1:	pla
	tax
	lda	#8
	ora	fd_table+ft_flag,x
	sta	fd_table+ft_flag,x
supp:	sec
	rts

notsupp:pla
ns1:	clc
	rts