string.c
3.32 KB
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/*
* 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.
*
* SPDX-License-Identifier: GPL-2.0+
*/
/* 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;
}
#define OP_T_THRES 8
#define OPSIZ (sizeof(op_t))
#define BYTE_COPY_FWD(dst_bp, src_bp, nbytes) \
do { \
int __d0; \
asm volatile( \
/* Clear the direction flag, so copying goes forward. */ \
"cld\n" \
/* Copy bytes. */ \
"rep\n" \
"movsb" : \
"=D" (dst_bp), "=S" (src_bp), "=c" (__d0) : \
"0" (dst_bp), "1" (src_bp), "2" (nbytes) : \
"memory"); \
} while (0)
#define WORD_COPY_FWD(dst_bp, src_bp, nbytes_left, nbytes) \
do { \
int __d0; \
asm volatile( \
/* Clear the direction flag, so copying goes forward. */ \
"cld\n" \
/* Copy longwords. */ \
"rep\n" \
"movsl" : \
"=D" (dst_bp), "=S" (src_bp), "=c" (__d0) : \
"0" (dst_bp), "1" (src_bp), "2" ((nbytes) / 4) : \
"memory"); \
(nbytes_left) = (nbytes) % 4; \
} while (0)
void *memcpy(void *dstpp, const void *srcpp, size_t len)
{
unsigned long int dstp = (long int)dstpp;
unsigned long int srcp = (long int)srcpp;
/* Copy from the beginning to the end. */
/* If there not too few bytes to copy, use word copy. */
if (len >= OP_T_THRES) {
/* Copy just a few bytes to make DSTP aligned. */
len -= (-dstp) % OPSIZ;
BYTE_COPY_FWD(dstp, srcp, (-dstp) % OPSIZ);
/* Copy from SRCP to DSTP taking advantage of the known
* alignment of DSTP. Number of bytes remaining is put
* in the third argument, i.e. in LEN. This number may
* vary from machine to machine.
*/
WORD_COPY_FWD(dstp, srcp, len, len);
/* Fall out and copy the tail. */
}
/* There are just a few bytes to copy. Use byte memory operations. */
BYTE_COPY_FWD(dstp, srcp, len);
return dstpp;
}