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memmove.c

/*
 * Copyright (C) 2008-2009 Michal Simek <monstr@monstr.eu>
 * Copyright (C) 2008-2009 PetaLogix
 * Copyright (C) 2007 John Williams
 *
 * Reasonably optimised generic C-code for memcpy on Microblaze
 * This is generic C code to do efficient, alignment-aware memmove.
 *
 * It is based on demo code originally Copyright 2001 by Intel Corp, taken from
 * http://www.embedded.com/showArticle.jhtml?articleID=19205567
 *
 * Attempts were made, unsuccesfully, to contact the original
 * author of this code (Michael Morrow, Intel).  Below is the original
 * copyright notice.
 *
 * This software has been developed by Intel Corporation.
 * Intel specifically disclaims all warranties, express or
 * implied, and all liability, including consequential and
 * other indirect damages, for the use of this program, including
 * liability for infringement of any proprietary rights,
 * and including the warranties of merchantability and fitness
 * for a particular purpose. Intel does not assume any
 * responsibility for and errors which may appear in this program
 * not any responsibility to update it.
 */

#include <linux/types.h>
#include <linux/stddef.h>
#include <linux/compiler.h>
#include <linux/module.h>
#include <linux/string.h>

#ifdef __HAVE_ARCH_MEMMOVE
void *memmove(void *v_dst, const void *v_src, __kernel_size_t c)
{
      const char *src = v_src;
      char *dst = v_dst;

#ifdef CONFIG_OPT_LIB_FUNCTION
      const uint32_t *i_src;
      uint32_t *i_dst;
#endif

      if (!c)
            return v_dst;

      /* Use memcpy when source is higher than dest */
      if (v_dst <= v_src)
            return memcpy(v_dst, v_src, c);

#ifndef CONFIG_OPT_LIB_FUNCTION
      /* copy backwards, from end to beginning */
      src += c;
      dst += c;

      /* Simple, byte oriented memmove. */
      while (c--)
            *--dst = *--src;

      return v_dst;
#else
      /* The following code tries to optimize the copy by using unsigned
       * alignment. This will work fine if both source and destination are
       * aligned on the same boundary. However, if they are aligned on
       * different boundaries shifts will be necessary. This might result in
       * bad performance on MicroBlaze systems without a barrel shifter.
       */
      /* FIXME this part needs more test */
      /* Do a descending copy - this is a bit trickier! */
      dst += c;
      src += c;

      if (c >= 4) {
            unsigned  value, buf_hold;

            /* Align the destination to a word boundry. */
            /* This is done in an endian independant manner. */

            switch ((unsigned long)dst & 3) {
            case 3:
                  *--dst = *--src;
                  --c;
            case 2:
                  *--dst = *--src;
                  --c;
            case 1:
                  *--dst = *--src;
                  --c;
            }

            i_dst = (void *)dst;
            /* Choose a copy scheme based on the source */
            /* alignment relative to dstination. */
            switch ((unsigned long)src & 3) {
            case 0x0:   /* Both byte offsets are aligned */

                  i_src  = (const void *)src;

                  for (; c >= 4; c -= 4)
                        *--i_dst = *--i_src;

                  src  = (const void *)i_src;
                  break;
            case 0x1:   /* Unaligned - Off by 1 */
                  /* Word align the source */
                  i_src = (const void *) (((unsigned)src + 4) & ~3);

                  /* Load the holding buffer */
                  buf_hold = *--i_src >> 24;

                  for (; c >= 4; c -= 4) {
                        value = *--i_src;
                        *--i_dst = buf_hold << 8 | value;
                        buf_hold = value >> 24;
                  }

                  /* Realign the source */
                  src = (const void *)i_src;
                  src += 1;
                  break;
            case 0x2:   /* Unaligned - Off by 2 */
                  /* Word align the source */
                  i_src = (const void *) (((unsigned)src + 4) & ~3);

                  /* Load the holding buffer */
                  buf_hold = *--i_src >> 16;

                  for (; c >= 4; c -= 4) {
                        value = *--i_src;
                        *--i_dst = buf_hold << 16 | value;
                        buf_hold = value >> 16;
                  }

                  /* Realign the source */
                  src = (const void *)i_src;
                  src += 2;
                  break;
            case 0x3:   /* Unaligned - Off by 3 */
                  /* Word align the source */
                  i_src = (const void *) (((unsigned)src + 4) & ~3);

                  /* Load the holding buffer */
                  buf_hold = *--i_src >> 8;

                  for (; c >= 4; c -= 4) {
                        value = *--i_src;
                        *--i_dst = buf_hold << 24 | value;
                        buf_hold = value >> 8;
                  }

                  /* Realign the source */
                  src = (const void *)i_src;
                  src += 3;
                  break;
            }
            dst = (void *)i_dst;
      }

      /* simple fast copy, ... unless a cache boundry is crossed */
      /* Finish off any remaining bytes */
      switch (c) {
      case 4:
            *--dst = *--src;
      case 3:
            *--dst = *--src;
      case 2:
            *--dst = *--src;
      case 1:
            *--dst = *--src;
      }
      return v_dst;
#endif
}
EXPORT_SYMBOL(memmove);
#endif /* __HAVE_ARCH_MEMMOVE */

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