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/*
* Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
*
* 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 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., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301, USA.
*/
/** @file
*
* Optimised string operations
*
*/
FILE_LICENCE ( GPL2_OR_LATER );
#include <string.h>
/**
* Copy memory area
*
* @v dest Destination address
* @v src Source address
* @v len Length
* @ret dest Destination address
*/
void * __attribute__ (( noinline )) __memcpy ( void *dest, const void *src,
size_t len ) {
void *edi = dest;
const void *esi = src;
int discard_ecx;
/* We often do large dword-aligned and dword-length block
* moves. Using movsl rather than movsb speeds these up by
* around 32%.
*/
__asm__ __volatile__ ( "rep movsl"
: "=&D" ( edi ), "=&S" ( esi ),
"=&c" ( discard_ecx )
: "0" ( edi ), "1" ( esi ), "2" ( len >> 2 )
: "memory" );
__asm__ __volatile__ ( "rep movsb"
: "=&D" ( edi ), "=&S" ( esi ),
"=&c" ( discard_ecx )
: "0" ( edi ), "1" ( esi ), "2" ( len & 3 )
: "memory" );
return dest;
}
/**
* Copy memory area backwards
*
* @v dest Destination address
* @v src Source address
* @v len Length
* @ret dest Destination address
*/
void * __attribute__ (( noinline )) __memcpy_reverse ( void *dest,
const void *src,
size_t len ) {
void *edi = ( dest + len - 1 );
const void *esi = ( src + len - 1 );
int discard_ecx;
/* Assume memmove() is not performance-critical, and perform a
* bytewise copy for simplicity.
*/
__asm__ __volatile__ ( "std\n\t"
"rep movsb\n\t"
"cld\n\t"
: "=&D" ( edi ), "=&S" ( esi ),
"=&c" ( discard_ecx )
: "0" ( edi ), "1" ( esi ),
"2" ( len )
: "memory" );
return dest;
}
/**
* Copy (possibly overlapping) memory area
*
* @v dest Destination address
* @v src Source address
* @v len Length
* @ret dest Destination address
*/
void * __memmove ( void *dest, const void *src, size_t len ) {
if ( dest <= src ) {
return __memcpy ( dest, src, len );
} else {
return __memcpy_reverse ( dest, src, len );
}
}
/**
* Swap memory areas
*
* @v dest Destination address
* @v src Source address
* @v len Length
* @ret dest Destination address
*/
void * memswap ( void *dest, void *src, size_t len ) {
size_t discard_c;
int discard;
__asm__ __volatile__ ( "\n1:\n\t"
"dec %2\n\t"
"js 2f\n\t"
"movb (%0,%2), %b3\n\t"
"xchgb (%1,%2), %b3\n\t"
"movb %b3, (%0,%2)\n\t"
"jmp 1b\n\t"
"2:\n\t"
: "=r" ( src ), "=r" ( dest ),
"=&c" ( discard_c ), "=&q" ( discard )
: "0" ( src ), "1" ( dest ), "2" ( len )
: "memory" );
return dest;
}
/**
* Calculate length of string
*
* @v string String
* @ret len Length (excluding NUL)
*/
size_t strlen ( const char *string ) {
const char *discard_D;
size_t len_plus_one;
__asm__ __volatile__ ( "repne scasb\n\t"
"not %1\n\t"
: "=&D" ( discard_D ), "=&c" ( len_plus_one )
: "0" ( string ), "1" ( -1UL ), "a" ( 0 ) );
return ( len_plus_one - 1 );
}
/**
* Compare strings (up to a specified length)
*
* @v str1 First string
* @v str2 Second string
* @v len Maximum length
* @ret diff Difference
*/
int strncmp ( const char *str1, const char *str2, size_t len ) {
const void *discard_S;
const void *discard_D;
size_t discard_c;
int diff;
__asm__ __volatile__ ( "\n1:\n\t"
"dec %2\n\t"
"js 2f\n\t"
"lodsb\n\t"
"scasb\n\t"
"jne 3f\n\t"
"testb %b3, %b3\n\t"
"jnz 1b\n\t"
/* Equal */
"\n2:\n\t"
"xor %3, %3\n\t"
"jmp 4f\n\t"
/* Not equal; CF indicates difference */
"\n3:\n\t"
"sbb %3, %3\n\t"
"orb $1, %b3\n\t"
"\n4:\n\t"
: "=&S" ( discard_S ), "=&D" ( discard_D ),
"=&c" ( discard_c ), "=&a" ( diff )
: "0" ( str1 ), "1" ( str2 ), "2" ( len ) );
return diff;
}
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