/* PowerPC-32  sub_n -- Subtract two limb vectors of the same length > 0
 *			and store difference in a third limb vector.
 * Copyright (C) 1992, 1994, 1995, 1997, 1998 Free Software Foundation, Inc.
 *
 * This file is part of GnuPG.
 *
 * GnuPG is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * GnuPG is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

#include "sysdep.h"
#include "asm-syntax.h"


#ifndef USE_PPC_PATCHES

/*******************
 *  mpi_limb_t
 *  mpihelp_sub_n( mpi_ptr_t res_ptr,	(r3)
 *		   mpi_ptr_t s1_ptr,	(r4)
 *		   mpi_ptr_t s2_ptr,	(r5)
 *		   mpi_size_t size)	(r6)
 */

	.toc
	.extern mpihelp_sub_n[DS]
	.extern .mpihelp_sub_n
.csect [PR]
	.align 2
	.globl mpihelp_sub_n
	.globl .mpihelp_sub_n
	.csect mpihelp_sub_n[DS]
mpihelp_sub_n:
	.long .mpihelp_sub_n, TOC[tc0], 0
	.csect [PR]
.mpihelp_sub_n:
	mtctr	6		# copy size into CTR
	lwz	8,0(4)		# load least significant s1 limb
	lwz	0,0(5)		# load least significant s2 limb
	addi	3,3,-4		# offset res_ptr, it is updated before used
	subfc	7,0,8		# add least significant limbs, set cy
	bdz	Lend		# If done, skip loop
Loop:	lwzu	8,4(4)		# load s1 limb and update s1_ptr
	lwzu	0,4(5)		# load s2 limb and update s2_ptr
	stwu	7,4(3)		# store previous limb in load latency slot
	subfe	7,0,8		# add new limbs with cy, set cy
	bdnz	Loop		# decrement CTR and loop back
Lend:	stw	7,4(3)		# store ultimate result limb
	subfe	3,0,0		# load !cy into ...
	subfic	3,3,0		# ... return value register
	blr

#else

/* mp_limb_t mpn_sub_n (mp_ptr res_ptr, mp_srcptr s1_ptr, mp_srcptr s2_ptr,
			mp_size_t size)
   Calculate s1-s2 and put result in res_ptr; return borrow, 0 or 1.  */

/* Note on optimisation: This code is optimal for the 601.  Almost every other
   possible 2-unrolled inner loop will not be.	Also, watch out for the
   alignment...  */

EALIGN(mpihelp_sub_n,3,1)
/* Set up for loop below.  */
       mtcrf 0x01,%r6
       srwi. %r7,%r6,1
       mtctr %r7
       bt    31,2f

/* Set the carry (clear the borrow).  */
       subfc %r0,%r0,%r0
/* Adjust pointers for loop.  */
       addi  %r3,%r3,-4
       addi  %r4,%r4,-4
       addi  %r5,%r5,-4
       b     0f

2:     lwz   %r7,0(%r5)
       lwz   %r6,0(%r4)
       subfc %r6,%r7,%r6
       stw   %r6,0(%r3)
	beq   1f

/* Align start of loop to an odd word boundary to guarantee that the
   last two words can be fetched in one access (for 601).  This turns
   out to be important.  */
0:
       lwz   %r9,4(%r4)
       lwz   %r8,4(%r5)
       lwzu  %r6,8(%r4)
       lwzu  %r7,8(%r5)
       subfe %r8,%r8,%r9
       stw   %r8,4(%r3)
       subfe %r6,%r7,%r6
       stwu  %r6,8(%r3)
       bdnz  0b
/* Return the borrow. */
1:     subfe %r3,%r3,%r3
       neg   %r3,%r3
       blr
END(mpihelp_sub_n)
#endif
