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dnl Alpha mpn_rshift -- Shift a number right.
dnl Copyright (C) 1994, 1995, 2000 Free Software Foundation, Inc.
dnl This file is part of the GNU MP Library.
dnl The GNU MP Library is free software; you can redistribute it and/or modify
dnl it under the terms of the GNU Library General Public License as published by
dnl the Free Software Foundation; either version 2 of the License, or (at your
dnl option) any later version.
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 Library General Public
dnl License for more details.
dnl You should have received a copy of the GNU Library General Public License
dnl along with the GNU MP Library; see the file COPYING.LIB. If not, write to
dnl the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
dnl MA 02111-1307, USA.
include(`../config.m4')
dnl INPUT PARAMETERS
dnl res_ptr r16
dnl s1_ptr r17
dnl size r18
dnl cnt r19
dnl This code runs at 4.8 cycles/limb on the 21064. With infinite unrolling,
dnl it would take 4 cycles/limb. It should be possible to get down to 3
dnl cycles/limb since both ldq and stq can be paired with the other used
dnl instructions. But there are many restrictions in the 21064 pipeline that
dnl makes it hard, if not impossible, to get down to 3 cycles/limb:
dnl 1. ldq has a 3 cycle delay, srl and sll have a 2 cycle delay.
dnl 2. Only aligned instruction pairs can be paired.
dnl 3. The store buffer or silo might not be able to deal with the bandwidth.
ASM_START()
PROLOGUE(mpn_rshift)
ldq r4,0(r17) C load first limb
addq r17,8,r17
subq r31,r19,r7
subq r18,1,r18
and r18,4-1,r20 C number of limbs in first loop
sll r4,r7,r0 C compute function result
beq r20,$L0
subq r18,r20,r18
ALIGN(8)
$Loop0:
ldq r3,0(r17)
addq r16,8,r16
addq r17,8,r17
subq r20,1,r20
srl r4,r19,r5
sll r3,r7,r6
bis r3,r3,r4
bis r5,r6,r8
stq r8,-8(r16)
bne r20,$Loop0
$L0: beq r18,$Lend
ALIGN(8)
$Loop: ldq r3,0(r17)
addq r16,32,r16
subq r18,4,r18
srl r4,r19,r5
sll r3,r7,r6
ldq r4,8(r17)
srl r3,r19,r1
bis r5,r6,r8
stq r8,-32(r16)
sll r4,r7,r2
ldq r3,16(r17)
srl r4,r19,r5
bis r1,r2,r8
stq r8,-24(r16)
sll r3,r7,r6
ldq r4,24(r17)
srl r3,r19,r1
bis r5,r6,r8
stq r8,-16(r16)
sll r4,r7,r2
addq r17,32,r17
bis r1,r2,r8
stq r8,-8(r16)
bgt r18,$Loop
$Lend: srl r4,r19,r8
stq r8,0(r16)
ret r31,(r26),1
EPILOGUE(mpn_rshift)
ASM_END()
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