; CONTIG.M68 -- Counts the number of free blocks and maximum number of 
; contiguous free blocks on a disk.

; Mike Vandeman, Synanon Church
; May 31, 1983

; 06/05/84 Largely rewritten by Tom Dahlquist to make it 1) device
; independent, and 2) reentrant.

; 10/24/86 Bug fixed by Irwin Goldstein.  The bit map is read & tested in
; word units instead of longwords, because for some devices (most notably
; a 400 MB drive formatted to 13 logicals) where the bitmap does not use
; up all of the last longword, CONTIG was giving too many blocks free.
; (The LSR instruction was starting with the unused portion of the last
; longword.  This is probably due in part to the way the AM100/L swaps
; words around.)

; Usage: CONTIG devn:

	SEARCH 	SYS
	SEARCH 	SYSSYM
	RADIX	10			;use decimal arithmetic

;	Workspace map

	DSECT
DDB:	BLKB	D.DDB
MAXCNT:	LWORD	0
WRKSIZ=.

	PSECT
	PHDR	-1,PV$RSM,PH$REU!PH$REE	;set program header

;	A0 -> work area throughout this code.

CONTIG:	GETIMP	WRKSIZ,A0		; get required memory and
	CLEAR	@A0,WRKSIZ		; clear it.
	BYP				;find first non-blank character
	FSPEC	@A0			; get device specification...
	TST	D.FIL(A0)		; no file name allowed...
	JNE	ERROR			; die if one given.
	INIT	@A0
	MOV	#2,D.REC(A0)		;enter physical record # in DDB (start with 2)
	MOV	D.DVR(A0),A1		; A1 -> device driver
	MOV	^O24(A1),D0		; D0 = # of blocks on device

;	Throughout the  rest of the code the following register assignments
;	are used:
;	A2:  -> next word to be read from current bitmap block
;	D0:  decremented counter of total # of blocks on disk
;	D1:  total # of free blocks
;	D2:  counter of # of contig blocks in current area
;	D3:  decremented counter of words in current bitmap block
;	D4:  decremented counter of bits in current word
;	D5:  current word

	CLR	D1			; clear total free block counter and
	CLR	D2			; current contig space counter.

LOOP1:	READ	@A0			;read disk block
	MOV	D.BUF(A0),A2		;get address of buffer
	MOV	#255,D3			;# of words to be tested (-1)

LOOP2:	MOVW	(A2)+,D5		;get next word to be tested
	MOV	#15,D4			;# of bits to be tested (-1)
	
LOOP3:	LSRW	D5,#1			;get bit to test
	BCS	ONE			;one?
	INC	D1			;increment # of free blocks
	INC	D2			;increment # of contiguous free blocks
	BR	NXTBIT

ONE:	CMP	D2,MAXCNT(A0)		;new high for contig ?
	BLOS	1$			;no
	MOV	D2,MAXCNT(A0)		;yes, save it
1$:	CLR	D2			;start counting again
	
NXTBIT:	DEC	D0
	BEQ	DONE
	DBF	D4,LOOP3		;loop to next bit
	DBF	D3,LOOP2		;loop to the next longword
	CTRLC	EXIT			;let me out on a ^C
	INC	D.REC(A0)		; go get next block of bitmap...
	BR	LOOP1

DONE:	CMP	D2,MAXCNT(A0)		;new high for contig ?
	BLOS	TYPE			;no
	MOV	D2,MAXCNT(A0)		;yes, save it

TYPE:	TYPESP	<Total free blocks:>		;display # of free blocks
	DCVT	0,OT$TRM
	CRLF
	TYPESP	<Largest contiguous space:>	;display # contig free blocks
	MOV	MAXCNT(A0),D1
	DCVT	0,OT$TRM
	CRLF

EXIT:	EXIT

ERROR:	TYPECR	<?Syntax is:  CONTIG devn:>
	EXIT

	EVEN
	END

.