Better tabselect

Torbjorn Granlund tg at
Fri Apr 12 17:14:41 CEST 2013

I'd suggest to use the loop below for sparc64.  It limits `which' to be <
2^32 by creating the mask based on 32-bit comparison.  It would be
possible to replace "subcc o1,1,o1; subc ..." by "addcc o1,-1,o1; addxc
..." for newer chips, but I think that's no use.

I sincerely apologise for the odd number of insns in the loop.  :-)

(Note that we support >= 2^32 operand sizes in mpn for 64bit chips, but
that doesn't mean that the number of vectors in tabselect need to be
that large.)

	sllx	n, 3, stride
	mov	tp, tporig
	sub	n, 4, j
	brlz	j, L(outer_end)

	clr	data0
	clr	data1
	clr	data2
	clr	data3
	mov	tporig, tp
	mov	nents, i
	mov	which, %o1

L(top):	subcc	%o1, 1, %o1		C set carry iff o1 = 0
	ldx	[tp + 0], t0
	subc	%g0, %g0, mask
	ldx	[tp + 8], t1
	sub	i, 1, i
	ldx	[tp + 16], t2
	ldx	[tp + 24], t3
	add	tp, stride, tp
	and	t0, mask, t0
	and	t1, mask, t1
	or	t0, data0, data0
	and	t2, mask, t2
	or	t1, data1, data1
	and	t3, mask, t3
	or	t2, data2, data2
	brnz	i, L(top)
	 or	t3, data3, data3

	stx	data0, [rp + 0]
	subcc	j, 4, j
	stx	data1, [rp + 8]
	stx	data2, [rp + 16]
	stx	data3, [rp + 24]
	add	tporig, (4 * 8), tporig

	brgez	j, L(outer_loop)
	 add	rp, (4 * 8), rp


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