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/* alpha rshift
* Copyright (C) 1994, 1995, 1998, 1999,
* 2000, 2001, 2002 Free Software Foundation, Inc.
*
* This file is part of Libgcrypt.
*
* Libgcrypt is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* Libgcrypt 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*
* Note: This code is heavily based on the GNU MP Library.
* Actually it's the same code with only minor changes in the
* way the data is stored; this is to support the abstraction
* of an optional secure memory allocation which may be used
* to avoid revealing of sensitive data due to paging etc.
*/
/*******************
* mpi_limb_t
* _gcry_mpih_rshift( mpi_ptr_t wp, (r16)
* mpi_ptr_t up, (r17)
* mpi_size_t usize, (r18)
* unsigned cnt) (r19)
*
* This code runs at 4.8 cycles/limb on the 21064. With infinite unrolling,
* it would take 4 cycles/limb. It should be possible to get down to 3
* cycles/limb since both ldq and stq can be paired with the other used
* instructions. But there are many restrictions in the 21064 pipeline that
* makes it hard, if not impossible, to get down to 3 cycles/limb:
*
* 1. ldq has a 3 cycle delay, srl and sll have a 2 cycle delay.
* 2. Only aligned instruction pairs can be paired.
* 3. The store buffer or silo might not be able to deal with the bandwidth.
*/
.set noreorder
.set noat
.text
.align 3
.globl _gcry_mpih_rshift
.ent _gcry_mpih_rshift
_gcry_mpih_rshift:
.frame $30,0,$26,0
ldq $4,0($17) # load first limb
addq $17,8,$17
subq $31,$19,$7
subq $18,1,$18
and $18,4-1,$20 # number of limbs in first loop
sll $4,$7,$0 # compute function result
beq $20,.R0
subq $18,$20,$18
.align 3
.Roop0:
ldq $3,0($17)
addq $16,8,$16
addq $17,8,$17
subq $20,1,$20
srl $4,$19,$5
sll $3,$7,$6
bis $3,$3,$4
bis $5,$6,$8
stq $8,-8($16)
bne $20,.Roop0
.R0: beq $18,.Rend
.align 3
.Roop: ldq $3,0($17)
addq $16,32,$16
subq $18,4,$18
srl $4,$19,$5
sll $3,$7,$6
ldq $4,8($17)
srl $3,$19,$1
bis $5,$6,$8
stq $8,-32($16)
sll $4,$7,$2
ldq $3,16($17)
srl $4,$19,$5
bis $1,$2,$8
stq $8,-24($16)
sll $3,$7,$6
ldq $4,24($17)
srl $3,$19,$1
bis $5,$6,$8
stq $8,-16($16)
sll $4,$7,$2
addq $17,32,$17
bis $1,$2,$8
stq $8,-8($16)
bgt $18,.Roop
.Rend: srl $4,$19,$8
stq $8,0($16)
ret $31,($26),1
.end _gcry_mpih_rshift
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