dnl  ARM v6t2 mpn_gcd_1.

dnl  Based on the K7 gcd_1.asm, by Kevin Ryde.  Rehacked for ARM by Torbjörn
dnl  Granlund.

dnl  Copyright 2000-2002, 2005, 2009, 2011, 2012 Free Software Foundation, Inc.

dnl  This file is part of the GNU MP Library.
dnl
dnl  The GNU MP Library is free software; you can redistribute it and/or modify
dnl  it under the terms of either:
dnl
dnl    * the GNU Lesser General Public License as published by the Free
dnl      Software Foundation; either version 3 of the License, or (at your
dnl      option) any later version.
dnl
dnl  or
dnl
dnl    * the GNU General Public License as published by the Free Software
dnl      Foundation; either version 2 of the License, or (at your option) any
dnl      later version.
dnl
dnl  or both in parallel, as here.
dnl
dnl  The GNU MP Library is distributed in the hope that it will be useful, but
dnl  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
dnl  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
dnl  for more details.
dnl
dnl  You should have received copies of the GNU General Public License and the
dnl  GNU Lesser General Public License along with the GNU MP Library.  If not,
dnl  see https://www.gnu.org/licenses/.

include(`../config.m4')

C	     cycles/bit (approx)
C StrongARM	 -
C XScale	 -
C Cortex-A7	 ?
C Cortex-A8	 ?
C Cortex-A9	 5.3
C Cortex-A15	 3.5
C Numbers measured with: speed -CD -s8-32 -t24 mpn_gcd_1

C TODO
C  * Optimise inner-loop better.
C  * Push saving/restoring of callee-user regs into call code

C Threshold of when to call bmod when U is one limb.  Should be about
C (time_in_cycles(bmod_1,1) + call_overhead) / (cycles/bit).
define(`BMOD_THRES_LOG2', 7)

C INPUT PARAMETERS
define(`up',    `r0')
define(`n',     `r1')
define(`v0',    `r2')

ifdef(`BMOD_1_TO_MOD_1_THRESHOLD',,
  `define(`BMOD_1_TO_MOD_1_THRESHOLD',0xffffffff)')

ASM_START()
	TEXT
	ALIGN(16)
PROLOGUE(mpn_gcd_1)
	push	{r4, r7, lr}
	ldr	r3, [up]	C U low limb

	orr	r3, r3, v0
	rbit	r4, r3
	clz	r4, r4		C min(ctz(u0),ctz(v0))

	rbit	r12, v0
	clz	r12, r12
	mov	v0, v0, lsr r12

	mov	r7, v0

	cmp	n, #1
	bne	L(nby1)

C Both U and V are single limbs, reduce with bmod if u0 >> v0.
	ldr	r3, [up]
	cmp	v0, r3, lsr #BMOD_THRES_LOG2
	bhi	L(red1)

L(bmod):mov	r3, #0		C carry argument
	bl	mpn_modexact_1c_odd
	b	L(red0)

L(nby1):cmp	n, #BMOD_1_TO_MOD_1_THRESHOLD
	blo	L(bmod)

	bl	mpn_mod_1

L(red0):mov	r3, r0
L(red1):cmp	r3, #0
	rbit	r12, r3
	clz	r12, r12
	bne	L(mid)
	b	L(end)

	ALIGN(8)
L(top):	movcs	r3, r1		C if x-y < 0
	movcs	r7, r0		C use x,y-x
L(mid):	mov	r3, r3, lsr r12	C
	mov	r0, r3		C
	subs	r1, r7, r3	C
	rsb	r3, r7, r3	C
	rbit	r12, r1
	clz	r12, r12	C
	bne	L(top)		C

L(end):	mov	r0, r7, lsl r4
	pop	{r4, r7, pc}
EPILOGUE()