+;
+; Christian Groessler, May-2000
+; Moved from fdtable.s to it's own file by Daniel Serpell, 2009.
+;
+; Convert file descriptor to IOCB number
+;
+
+ .include "atari.inc"
+ .include "fd.inc"
+ .import fd_table,fd_index
+ .export fdtoiocb
+
+ .code
+
+; gets fd in ax
+; return iocb index in A, fd_table index in X
+; return N bit set for invalid fd
+; all registers destroyed
+.proc fdtoiocb
+
+ cpx #0
+ bne inval
+ cmp #MAX_FD_INDEX
+ bcs inval
+ tax
+ lda fd_index,x
+ asl a ; create index into fd table
+ asl a
+ tax
+ lda #$ff
+ cmp fd_table+ft_iocb,x ; entry in use?
+ beq inval ; no, return error
+ lda fd_table+ft_usa,x ; get usage counter
+ beq inval ; 0? should not happen
+ lda fd_table+ft_iocb,x ; get iocb
+ rts
+
+inval: ldx #$ff ; sets N
+ rts
+
+.endproc ; fdtoiocb