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/* Copyright (C) 1996 Free Software Foundation, Inc.
Contributed by Richard Henderson (rth@tamu.edu)
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
The GNU C 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
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA. */
/* Fill a block of memory with zeros. Optimized for the Alpha architecture:
- memory accessed as aligned quadwords only
- destination memory not read unless needed for good cache behaviour
- basic blocks arranged to optimize branch prediction for full-quadword
aligned memory blocks.
- partial head and tail quadwords constructed with byte-mask instructions
This is generally scheduled for the EV5 (got to look out for my own
interests :-), but with EV4 needs in mind. There *should* be no more
stalls for the EV4 than there are for the EV5.
*/
#include <sysdep.h>
.set noat
.set noreorder
.text
/* There is a problem with either gdb (as of 4.16) or gas (as of 2.7) that
doesn't like putting the entry point for a procedure somewhere in the
middle of the procedure descriptor. Work around this by putting the main
loop in its own procedure descriptor. */
/* On entry to this basic block:
t3 == loop counter
t4 == bytes in partial final word
a0 == possibly misaligned destination pointer */
.ent bzero_loop
.align 3
bzero_loop:
.frame sp, 0, ra, 0
.prologue 0
beq t3, $tail #
blbc t3, 0f # skip single store if count even
stq_u zero, 0(a0) # e0 : store one word
subq t3, 1, t3 # .. e1 :
addq a0, 8, a0 # e0 :
beq t3, $tail # .. e1 :
0: stq_u zero, 0(a0) # e0 : store two words
subq t3, 2, t3 # .. e1 :
stq_u zero, 8(a0) # e0 :
addq a0, 16, a0 # .. e1 :
bne t3, 0b # e1 :
$tail: bne t4, 1f # is there a tail to do?
ret # no
1: ldq_u t0, 0(a0) # yes, load original data
mskqh t0, t4, t0 #
stq_u t0, 0(a0) #
ret #
.end bzero_loop
ENTRY(bzero)
.prologue 0
mov a0, v0 # e0 : move return value in place
beq a1, $done # .. e1 : early exit for zero-length store
and a0, 7, t1 # e0 :
addq a1, t1, a1 # e1 : add dest misalignment to count
srl a1, 3, t3 # e0 : loop = count >> 3
and a1, 7, t4 # .. e1 : find number of bytes in tail
unop # :
beq t1, bzero_loop # e1 : aligned head, jump right in
ldq_u t0, 0(a0) # e0 : load original data to mask into
cmpult a1, 8, t2 # .. e1 : is this a sub-word set?
bne t2, $oneq # e1 :
mskql t0, a0, t0 # e0 : we span words. finish this partial
subq t3, 1, t3 # e0 :
addq a0, 8, a0 # .. e1 :
stq_u t0, -8(a0) # e0 :
br bzero_loop # .. e1 :
.align 3
$oneq:
mskql t0, a0, t2 # e0 :
mskqh t0, a1, t3 # e0 :
or t2, t3, t0 # e1 :
stq_u t0, 0(a0) # e0 :
$done: ret
END(bzero)
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