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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)