x86_string.c

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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.
 *
 * You can also choose to distribute this program under the terms of
 * the Unmodified Binary Distribution Licence (as given in the file
 * COPYING.UBDL), provided that you have satisfied its requirements.
 */

/** @file
 *
 * Optimised string operations
 *
 */

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );

#include <string.h>
#include <config/defaults.h>

/* Use generic_memcpy_reverse() if we cannot safely set the direction flag */
#ifdef UNSAFE_STD
#define USE_GENERIC_MEMCPY_REVERSE 1
#else
#define USE_GENERIC_MEMCPY_REVERSE 0
#endif

/**
 * 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;

        /* Use unoptimised version if we are not permitted to modify
         * the direction flag.
         */
        if ( USE_GENERIC_MEMCPY_REVERSE )
                return generic_memcpy_reverse ( dest, src, len );

        /* 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 );
        }
}