tst	(sp)+ / bump sp
	jsr	r0,3f / have found a free block
	bic	r3,(r2) / set bit for this block i.e. assign block
	br	2f

free:
	mov	r2,-(sp) / save r2, r3
	mov	r3,-(sp)
	jsr	r0,3f / set up bit mask and word no. in free storage map
		      / for block
	bis	r3,(r2) / set free storage block bit; indicates free block
2:
	mov	(sp)+,r3 / restore r2, r3
	mov	(sp)+,r2
	tst	cdev / cdev = 0, block structured, drum; cdev = 1
		     / mountable device
	bne	1f
	incb	smod / set super block modified for drum
	rts	r0
1:
	incb	mmod / set super block modified for mountable device
	rts	r0
3:
	mov	r1,r2 / block number, k, = 1
	bic	$!7,r2 / clear all bits but 0,1,2; r2 = (k) mod (8)
	clr	r3
	bisb	2f(r2),r3 / use mask to set bit in r3 corresponding to
			  / (k) mod 8
	mov	r1,r2 / divide block number by 16
	asr	r2
	asr	r2
	asr	r2
	asr	r2
	bcc	1f / branch if bit 3 in r1 was 0 i.e., bit for block is in
		   / lower half of word
	swab	r3 / swap bytes in r3; bit in upper half of word in free
		   / storage map
1:
	asl	r2 / multiply block number by 2; r2 = k/8
	add	$systm+2,r2 / address of word of free storage map for drum
	    		    / with block bit in it
	tst	cdev
	beq	1f / cdev = 0 indicates device is drum
	add	$mount-systm,r2 / address of word of free storage map for
				/ mountable device with bit of block to be
				/ freed
1:
	rts	r0 / return to 'free'
2:
	.byte	1,2,4,10,20,40,100,200 / masks for bits 0,...,7

access:
	jsr	r0,iget / read in i-node for current directory (i-number
			/ passed in r1)
	mov	i.flgs,r2