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glibc/ports/sysdeps/alpha/rshift.S
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# Alpha 21064 __mpn_rshift -- | |
# Copyright (C) 1994, 1995 Free Software Foundation, Inc. | |
# This file is part of the GNU MP Library. | |
# The GNU MP Library 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. | |
# The GNU MP Library 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 the GNU MP Library. If not, see <http://www.gnu.org/licenses/>. | |
# INPUT PARAMETERS | |
# res_ptr r16 | |
# s1_ptr r17 | |
# size r18 | |
# 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 __mpn_rshift | |
.ent __mpn_rshift | |
__mpn_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,.L0 | |
subq $18,$20,$18 | |
.align 3 | |
.Loop0: | |
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,.Loop0 | |
.L0: beq $18,.Lend | |
.align 3 | |
.Loop: 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,.Loop | |
.Lend: srl $4,$19,$8 | |
stq $8,0($16) | |
ret $31,($26),1 | |
.end __mpn_rshift |