string/memmove.c

   1 /* Copy memory to memory until the specified number of bytes
   2    has been copied.  Overlap is handled correctly.
   3    Copyright (C) 1991-2024 Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <https://www.gnu.org/licenses/>.  */
  19
  20 #include <string.h>
  21 #include <memcopy.h>
  22
  23 /* All this is so that bcopy.c can #include
  24    this file after defining some things.  */
  25 #ifndef a1
  26 #define a1      dest    /* First arg is DEST.  */
  27 #define a1const
  28 #define a2      src     /* Second arg is SRC.  */
  29 #define a2const const
  30 #undef memmove
  31 #endif
  32 #if     !defined(RETURN) || !defined(rettype)
  33 #define RETURN(s)       return (s)      /* Return DEST.  */
  34 #define rettype         void *
  35 #endif
  36
  37 #ifndef MEMMOVE
  38 #define MEMMOVE memmove
  39 #endif
  40
  41 rettype
  42 inhibit_loop_to_libcall
  43 MEMMOVE (a1const void *a1, a2const void *a2, size_t len)
  44 {
  45   unsigned long int dstp = (long int) dest;
  46   unsigned long int srcp = (long int) src;
  47
  48   /* This test makes the forward copying code be used whenever possible.
  49      Reduces the working set.  */
  50   if (dstp - srcp >= len)       /* *Unsigned* compare!  */
  51     {
  52       /* Copy from the beginning to the end.  */
  53
  54 #if MEMCPY_OK_FOR_FWD_MEMMOVE
  55       dest = memcpy (dest, src, len);
  56 #else
  57       /* If there not too few bytes to copy, use word copy.  */
  58       if (len >= OP_T_THRES)
  59         {
  60           /* Copy just a few bytes to make DSTP aligned.  */
  61           len -= (-dstp) % OPSIZ;
  62           BYTE_COPY_FWD (dstp, srcp, (-dstp) % OPSIZ);
  63
  64           /* Copy whole pages from SRCP to DSTP by virtual address
  65              manipulation, as much as possible.  */
  66
  67           PAGE_COPY_FWD_MAYBE (dstp, srcp, len, len);
  68
  69           /* Copy from SRCP to DSTP taking advantage of the known
  70              alignment of DSTP.  Number of bytes remaining is put
  71              in the third argument, i.e. in LEN.  This number may
  72              vary from machine to machine.  */
  73
  74           WORD_COPY_FWD (dstp, srcp, len, len);
  75
  76           /* Fall out and copy the tail.  */
  77         }
  78
  79       /* There are just a few bytes to copy.  Use byte memory operations.  */
  80       BYTE_COPY_FWD (dstp, srcp, len);
  81 #endif /* MEMCPY_OK_FOR_FWD_MEMMOVE */
  82     }
  83   else
  84     {
  85       /* Copy from the end to the beginning.  */
  86       srcp += len;
  87       dstp += len;
  88
  89       /* If there not too few bytes to copy, use word copy.  */
  90       if (len >= OP_T_THRES)
  91         {
  92           /* Copy just a few bytes to make DSTP aligned.  */
  93           len -= dstp % OPSIZ;
  94           BYTE_COPY_BWD (dstp, srcp, dstp % OPSIZ);
  95
  96           /* Copy from SRCP to DSTP taking advantage of the known
  97              alignment of DSTP.  Number of bytes remaining is put
  98              in the third argument, i.e. in LEN.  This number may
  99              vary from machine to machine.  */
 100
 101           WORD_COPY_BWD (dstp, srcp, len, len);
 102
 103           /* Fall out and copy the tail.  */
 104         }
 105
 106       /* There are just a few bytes to copy.  Use byte memory operations.  */
 107       BYTE_COPY_BWD (dstp, srcp, len);
 108     }
 109
 110   RETURN (dest);
 111 }
 112 #ifndef memmove
 113 libc_hidden_builtin_def (memmove)
 114 #endif