V10/cmd/PDP11/crt/ulrem.s

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/ Unsigned long remainder

.globl	ulrem
.globl	csv, cret
ulrem:
	jsr	r5,csv
	tst	8.(r5)
	bne	hardlrem
	mov	10.(r5),r3
	bmi	hardlrem
	mov	6.(r5),r2
	mov	4.(r5),r1
	bmi	hardest
	clr	r0
	div	r3,r0
	mov	r1,r0
	mov	r2,r1
	div	r3,r0
	bvc	1f
	sub	r3,r0		/ this is the clever part
	div	r3,r0
	tst	r1
	beq	1f
	add	r3,r1
1:
	clr	r0
	jmp	cret

/ The divisor is known to be >= 2^15 so only 16 cycles are needed.
hardlrem:
	mov	6.(r5),r2
	mov	4.(r5),r1
	clr	r0
	mov	8.(r5),r3
	mov	$16.,r4
1:
	clc
	rol	r2
	rol	r1
	rol	r0
	cmp	r3,r0
	bhi	3f
	blo	2f
	cmp	10.(r5),r1
	blos	2f
3:
	sob	r4,1b
	br	1f
2:
	sub	10.(r5),r1
	sbc	r0
	sub	r3,r0
	sob	r4,1b
1:
	jmp	cret

/ The dividend is known to be >= 2^31 so 32 cycles are needed.
hardest:
	mov	6.(r5),r3
	mov	4.(r5),r2
	clr	r1
	clr	r0
	mov	$32.,r4
1:
	clc
	rol	r3
	rol	r2
	rol	r1
	rol	r0
	cmp	8.(r5),r0
	bhi	3f
	blo	2f
	cmp	10.(r5),r1
	blos	2f
3:
	sob	r4,1b
	br	1f
2:
	sub	10.(r5),r1
	sbc	r0
	sub	8.(r5),r0
	sob	r4,1b
1:
	jmp	cret