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x86: Import the glibc memset implementation

Browse source 
The new implementation is about twice as fast as the old. This is from
glibc-2.14, sysdeps/i386/memset.c.

Signed-off-by: Gabe Black <gabeblack@chromium.org>
This commit is contained in:
Gabe Black 2011-11-14 14:47:18 +00:00 committed by Graeme Russ
parent 60a9b6bfdd
commit dbaef6ef33
3 changed files with 89 additions and 1 deletions
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2
arch/x86/include/asm/string.h
View file

@ -23,7 +23,7 @@ extern void * memmove(void *, const void *, __kernel_size_t);
#undef __HAVE_ARCH_MEMCHR
extern void * memchr(const void *, int, __kernel_size_t);
#undef __HAVE_ARCH_MEMSET
#define __HAVE_ARCH_MEMSET
extern void * memset(void *, int, __kernel_size_t);
#undef __HAVE_ARCH_MEMZERO

1
arch/x86/lib/Makefile
View file

@ -38,6 +38,7 @@ COBJS-$(CONFIG_SYS_GENERIC_TIMER) += pcat_timer.o
COBJS-$(CONFIG_PCI) += pci.o
COBJS-$(CONFIG_PCI) += pci_type1.o
COBJS-$(CONFIG_SYS_X86_REALMODE) += realmode.o
COBJS-y += string.o
COBJS-$(CONFIG_SYS_X86_ISR_TIMER) += timer.o
COBJS-$(CONFIG_VIDEO) += video_bios.o
COBJS-$(CONFIG_VIDEO) += video.o

87
arch/x86/lib/string.c Normal file
View file

@ -0,0 +1,87 @@
/*
* Copyright (C) 1991,1992,1993,1997,1998,2003, 2005 Free Software Foundation, Inc.
* This file is part of the GNU C Library.
* Copyright (c) 2011 The Chromium OS Authors.
*
* See file CREDITS for list of people who contributed to this
* project.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of
* the License, or (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston,
* MA 02111-1307 USA
*/
/* From glibc-2.14, sysdeps/i386/memset.c */
#include <compiler.h>
#include <asm/string.h>
#include <linux/types.h>
typedef uint32_t op_t;
void *memset(void *dstpp, int c, size_t len)
{
int d0;
unsigned long int dstp = (unsigned long int) dstpp;
/* This explicit register allocation improves code very much indeed. */
register op_t x asm("ax");
x = (unsigned char) c;
/* Clear the direction flag, so filling will move forward. */
asm volatile("cld");
/* This threshold value is optimal. */
if (len >= 12) {
/* Fill X with four copies of the char we want to fill with. */
x |= (x << 8);
x |= (x << 16);
/* Adjust LEN for the bytes handled in the first loop. */
len -= (-dstp) % sizeof(op_t);
/*
* There are at least some bytes to set. No need to test for
* LEN == 0 in this alignment loop.
*/
/* Fill bytes until DSTP is aligned on a longword boundary. */
asm volatile(
"rep\n"
"stosb" /* %0, %2, %3 */ :
"=D" (dstp), "=c" (d0) :
"0" (dstp), "1" ((-dstp) % sizeof(op_t)), "a" (x) :
"memory");
/* Fill longwords. */
asm volatile(
"rep\n"
"stosl" /* %0, %2, %3 */ :
"=D" (dstp), "=c" (d0) :
"0" (dstp), "1" (len / sizeof(op_t)), "a" (x) :
"memory");
len %= sizeof(op_t);
}
/* Write the last few bytes. */
asm volatile(
"rep\n"
"stosb" /* %0, %2, %3 */ :
"=D" (dstp), "=c" (d0) :
"0" (dstp), "1" (len), "a" (x) :
"memory");
return dstpp;
}