minix/common/lib/libc/arch/x86_64/string/memset.S

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/* $NetBSD: memset.S,v 1.3 2009/08/01 20:35:45 dsl Exp $ */
/*-
* Copyright (c) 2009 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by David Laight.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <machine/asm.h>
#if defined(LIBC_SCCS)
RCSID("$NetBSD: memset.S,v 1.3 2009/08/01 20:35:45 dsl Exp $")
#endif
#ifndef _KERNEL
/* bzero, %rdi is buffer, %rsi length */
ENTRY(bzero)
mov %rsi,%rdx /* length */
xor %eax,%eax /* value to write */
jmp 1f
#endif
/* memset, %rdi is buffer, %rsi char to fill, %rdx length */
ENTRY(memset)
movzbq %sil,%rax /* byte value to fill */
mov %rdx,%rsi /* copy of length */
mov $0x0101010101010101,%r9
imul %r9,%rax /* fill value in all bytes */
1:
mov %rdi,%r9 /* Need to return buffer address */
or %edi,%edx /* address | length */
mov %rsi,%rcx
cmp $7,%rsi
jbe 10f /* jump if short fill */
test $7,%dl /* check for misaligned fill */
jnz 20f /* jump if misaligned */
/* Target aligned and length multiple of 8 */
2:
shr $3,%rcx
rep stosq
mov %r9,%rax
ret
/*
* Short transfer, any faffing here will generate mispredicted branches.
* So we keep it simple.
*/
10: rep stosb
mov %r9,%rax
ret
/*
* Buffer or length misaligned.
* Write pattern to first and last word of buffer, then fill middle.
* (This writes to some bytes more than once - possibly three times!.)
*/
20:
mov %rax,(%rdi)
movzbq %dil,%rdx /* low address for alignment */
mov %rax,-8(%rcx,%rdi)
and $7,%dl /* offset in word */
sub %rdx,%rcx /* adjust length ... */
add %rdx,%rdi /* ... and target */
jmp 2b