title	Calculate Free Space On A Drive
	name	('GETFREE')

; Return the number of unallocated kilobytes
; of space on the currently logged drive

bdos	equ	5
tbuff	equ	0080h

	entry	get_freek

	entry	extmsk

; Enter:	a = drive (0=A:, ..., 15=P:)
; Exit:		hl = free space on drive, in Kilobytes
;
get_freek:
	ld	(spacedrv),a	; save drive
	ld	e,a
	ld	c,14		; BDOS select disk function
	call	bdos
;
; check for CP/M Plus
;
	ld	c,12		; get bdos Version
	call	bdos		; if not cp/m 3 System
	cp	30h
	jr	c,dparams	; ..jump to calculate from alv
;
; calculate free space for CP/M Plus
;
	ld	de,tbuff	; set default dma
	ld	c,26
	call	bdos
	ld	c,46		; get disk freespace
	ld	a,(spacedrv)
	ld	e,a		; ..on this drive
	call	bdos
;
; Disk space is returned by CPM+ at dma for 3 bytes.
;
	ld	hl,(tbuff)	; Low to L, Mid to H
	ld	a,(tbuff+2)	; High to A
	ld	b,3		; Divide by 8 (SHR 3)
;
; Shift everything right into HL (64 MB max reportable)
;
div:	or	a		; Clear carry
	rra			; High
	rr	h		; Mid
	rr	l		; Low
	djnz	div
	ret			; hl = space free in Kbytes
;
; For CP/M 2 use this method:
;
dparams:
	ld	c,31		; BDOS get disk parameters function
	call	bdos
	inc	hl		; point to block shift-factor byte
	inc	hl
	ld	a,(hl)		; Get value and
	ld	(blkshf),a	; ..save it
	inc	hl		; point to max data block number
	inc	hl
	ld	a,(hl)
	ld	(extmsk),a	; save it
	inc	hl
	ld	e,(hl)		; Get (word) value into DE
	inc	hl
	ld	d,(hl)
	inc	de		; Add 1 for max number of blocks

; Compute amount of free space left on disk

dfree:	ld	c,27		; BDOS get allocation vector function
	push	de		; Save BLKMAX value
	call	bdos		; Get allocation vector into
	ld	b,h		; ..BC
	ld	c,l
	pop	hl		; Restore BLKMAX value to HL
	ld	de,0		; Inititialize count of free blocks

; At this point we have
;	BC = allocation vector address
;	DE = free block count
;	HL = number of data blocks on disk

cntfree:
	push   bc		; Save allocation map ptr
	ld     a,(bc)		; Get bit pattern of allocation byte
	ld     b,8		; Set to process 8 blocks
;
cnt2:	rla			; Rotate allocated block bit into carry flag
	jr	c,cnt3		; If set (bit=1), block is allocated
	inc	de		; If not set, block is not allocated, so
				; ..increment free block count
;
cnt3:	ld	c,a		; Save remaining allocation bits in C
	dec	hl		; Count down number of blocks on disk
	ld	a,l		; if down to zero
	or	h
	jr	z,cnt4		; ..branch
	ld	a,c		; Get back current allocation bit pattern
	djnz	cnt2		; Loop through 8 bits
	pop	bc		; Get ptr to allocation vector
	inc	bc		; Point to next allocation byte
	jr	cntfree		; Process next allocation byte

cnt4:	pop	bc		; clear stack
	ex	de,hl		; Free block count to HL
;
	ld	a,(blkshf)	; Get block shift factor
	sub	3		; Convert to log2 of K per block
	ret	z		; Done if 1K per block

; Convert for data blocks of more than 1K each

free2k:	add	hl,hl
	dec	a
	jr	nz,free2k
	ret			; HL * amount of free space on disk in K
;
spacedrv:ds	1
blkshf:	ds	1
extmsk:	ds	1

	end