glibc/sysdeps/x86_64/memset.S

/* memset/bzero -- set memory area to CH/0
   Optimized version for x86-64.
   Copyright (C) 2002, 2003 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Andreas Jaeger <aj@suse.de>.

   The GNU C 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 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <sysdep.h>
#include "asm-syntax.h"
#include "bp-sym.h"
#include "bp-asm.h"

/* BEWARE: `#ifdef memset' means that memset is redefined as `bzero' */
#define BZERO_P (defined memset)

/* This is somehow experimental and could made dependend on the cache
   size.  */
#define LARGE $120000

        .text
ENTRY (memset)
#if BZERO_P
	mov	%rsi,%rdx	/* Adjust parameter.  */
	xorq	%rsi,%rsi	/* Fill with 0s.  */
#endif
	cmp	$0x7,%rdx	/* Check for small length.  */
	mov	%rdi,%rcx	/* Save ptr as return value.  */
	jbe	7f

#if BZERO_P
	mov	%rsi,%r8	/* Just copy 0.  */
#else
	/* Populate 8 bit data to full 64-bit.  */
	movabs	$0x0101010101010101,%r8
	movzbl	%sil,%eax
	imul	%rax,%r8
#endif
	test	$0x7,%edi	/* Check for alignment.  */
	je	2f

	.p2align 4
1:	/* Align ptr to 8 byte.  */
	mov	%sil,(%rcx)
	dec	%rdx
	inc	%rcx
	test	$0x7,%ecx
	jne	1b

2:	/* Check for really large regions.  */
	mov	%rdx,%rax
	shr	$0x6,%rax
	je	4f
	cmp	LARGE, %rdx
	jae	11f

	.p2align 4
3:	/* Copy 64 bytes.  */
	mov	%r8,(%rcx)
	mov	%r8,0x8(%rcx)
	mov	%r8,0x10(%rcx)
	mov	%r8,0x18(%rcx)
	mov	%r8,0x20(%rcx)
	mov	%r8,0x28(%rcx)
	mov	%r8,0x30(%rcx)
	mov	%r8,0x38(%rcx)
	add	$0x40,%rcx
	dec	%rax
	jne	3b

4:	/* Copy final bytes.  */
	and	$0x3f,%edx
	mov	%rdx,%rax
	shr	$0x3,%rax
	je	6f

5:	/* First in chunks of 8 bytes.  */
	mov	%r8,(%rcx)
	add	$0x8,%rcx
	dec	%rax
	jne	5b
6:
	and	$0x7,%edx
7:
	test	%rdx,%rdx
	je	9f
8:	/* And finally as bytes (up to 7).  */
	mov	%sil,(%rcx)
	inc	%rcx
	dec	%rdx
	jne	8b
9:
#if BZERO_P
	nop
#else
	/* Load result (only if used as memset).  */
	mov	%rdi,%rax	/* start address of destination is result */
#endif
	retq

	.p2align 4
11:	/* Copy 64 bytes without polluting the cache.  */
	/* We could use	movntdq    %xmm0,(%rcx) here to further
	   speed up for large cases but let's not use XMM registers.  */
	movnti	%r8,(%rcx)
	movnti  %r8,0x8(%rcx)
	movnti  %r8,0x10(%rcx)
	movnti  %r8,0x18(%rcx)
	movnti  %r8,0x20(%rcx)
	movnti  %r8,0x28(%rcx)
	movnti  %r8,0x30(%rcx)
	movnti  %r8,0x38(%rcx)
	add	$0x40,%rcx
	dec	%rax
	jne	11b
	jmp	4b

END (memset)
#if !BZERO_P
libc_hidden_builtin_def (memset)
#endif