sysdeps/generic/memcopy.h

   1 /* memcopy.h -- definitions for memory copy functions.  Generic C version.
   2    Copyright (C) 1991-2014 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Torbjorn Granlund (tege@sics.se).
   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    <http://www.gnu.org/licenses/>.  */
  19
  20 #ifndef _MEMCOPY_H
  21 #define _MEMCOPY_H      1
  22
  23 /* The strategy of the memory functions is:
  24
  25      1. Copy bytes until the destination pointer is aligned.
  26
  27      2. Copy words in unrolled loops.  If the source and destination
  28      are not aligned in the same way, use word memory operations,
  29      but shift and merge two read words before writing.
  30
  31      3. Copy the few remaining bytes.
  32
  33    This is fast on processors that have at least 10 registers for
  34    allocation by GCC, and that can access memory at reg+const in one
  35    instruction.
  36
  37    I made an "exhaustive" test of this memmove when I wrote it,
  38    exhaustive in the sense that I tried all alignment and length
  39    combinations, with and without overlap.  */
  40
  41 #include <sys/cdefs.h>
  42 #include <endian.h>
  43
  44 /* The macros defined in this file are:
  45
  46    BYTE_COPY_FWD(dst_beg_ptr, src_beg_ptr, nbytes_to_copy)
  47
  48    BYTE_COPY_BWD(dst_end_ptr, src_end_ptr, nbytes_to_copy)
  49
  50    WORD_COPY_FWD(dst_beg_ptr, src_beg_ptr, nbytes_remaining, nbytes_to_copy)
  51
  52    WORD_COPY_BWD(dst_end_ptr, src_end_ptr, nbytes_remaining, nbytes_to_copy)
  53
  54    MERGE(old_word, sh_1, new_word, sh_2)
  55      [I fail to understand.  I feel stupid.  --roland]
  56 */
  57
  58 /* Type to use for aligned memory operations.
  59    This should normally be the biggest type supported by a single load
  60    and store.  */
  61 #define op_t    unsigned long int
  62 #define OPSIZ   (sizeof(op_t))
  63
  64 /* Type to use for unaligned operations.  */
  65 typedef unsigned char byte;
  66
  67 #if __BYTE_ORDER == __LITTLE_ENDIAN
  68 #define MERGE(w0, sh_1, w1, sh_2) (((w0) >> (sh_1)) | ((w1) << (sh_2)))
  69 #endif
  70 #if __BYTE_ORDER == __BIG_ENDIAN
  71 #define MERGE(w0, sh_1, w1, sh_2) (((w0) << (sh_1)) | ((w1) >> (sh_2)))
  72 #endif
  73
  74 /* Copy exactly NBYTES bytes from SRC_BP to DST_BP,
  75    without any assumptions about alignment of the pointers.  */
  76 #define BYTE_COPY_FWD(dst_bp, src_bp, nbytes)                                 \
  77   do                                                                          \
  78     {                                                                         \
  79       size_t __nbytes = (nbytes);                                             \
  80       while (__nbytes > 0)                                                    \
  81         {                                                                     \
  82           byte __x = ((byte *) src_bp)[0];                                    \
  83           src_bp += 1;                                                        \
  84           __nbytes -= 1;                                                      \
  85           ((byte *) dst_bp)[0] = __x;                                         \
  86           dst_bp += 1;                                                        \
  87         }                                                                     \
  88     } while (0)
  89
  90 /* Copy exactly NBYTES_TO_COPY bytes from SRC_END_PTR to DST_END_PTR,
  91    beginning at the bytes right before the pointers and continuing towards
  92    smaller addresses.  Don't assume anything about alignment of the
  93    pointers.  */
  94 #define BYTE_COPY_BWD(dst_ep, src_ep, nbytes)                                 \
  95   do                                                                          \
  96     {                                                                         \
  97       size_t __nbytes = (nbytes);                                             \
  98       while (__nbytes > 0)                                                    \
  99         {                                                                     \
 100           byte __x;                                                           \
 101           src_ep -= 1;                                                        \
 102           __x = ((byte *) src_ep)[0];                                         \
 103           dst_ep -= 1;                                                        \
 104           __nbytes -= 1;                                                      \
 105           ((byte *) dst_ep)[0] = __x;                                         \
 106         }                                                                     \
 107     } while (0)
 108
 109 /* Copy *up to* NBYTES bytes from SRC_BP to DST_BP, with
 110    the assumption that DST_BP is aligned on an OPSIZ multiple.  If
 111    not all bytes could be easily copied, store remaining number of bytes
 112    in NBYTES_LEFT, otherwise store 0.  */
 113 extern void _wordcopy_fwd_aligned (long int, long int, size_t) __THROW;
 114 extern void _wordcopy_fwd_dest_aligned (long int, long int, size_t) __THROW;
 115 #define WORD_COPY_FWD(dst_bp, src_bp, nbytes_left, nbytes)                    \
 116   do                                                                          \
 117     {                                                                         \
 118       if (src_bp % OPSIZ == 0)                                                \
 119         _wordcopy_fwd_aligned (dst_bp, src_bp, (nbytes) / OPSIZ);             \
 120       else                                                                    \
 121         _wordcopy_fwd_dest_aligned (dst_bp, src_bp, (nbytes) / OPSIZ);        \
 122       src_bp += (nbytes) & -OPSIZ;                                            \
 123       dst_bp += (nbytes) & -OPSIZ;                                            \
 124       (nbytes_left) = (nbytes) % OPSIZ;                                       \
 125     } while (0)
 126
 127 /* Copy *up to* NBYTES_TO_COPY bytes from SRC_END_PTR to DST_END_PTR,
 128    beginning at the words (of type op_t) right before the pointers and
 129    continuing towards smaller addresses.  May take advantage of that
 130    DST_END_PTR is aligned on an OPSIZ multiple.  If not all bytes could be
 131    easily copied, store remaining number of bytes in NBYTES_REMAINING,
 132    otherwise store 0.  */
 133 extern void _wordcopy_bwd_aligned (long int, long int, size_t) __THROW;
 134 extern void _wordcopy_bwd_dest_aligned (long int, long int, size_t) __THROW;
 135 #define WORD_COPY_BWD(dst_ep, src_ep, nbytes_left, nbytes)                    \
 136   do                                                                          \
 137     {                                                                         \
 138       if (src_ep % OPSIZ == 0)                                                \
 139         _wordcopy_bwd_aligned (dst_ep, src_ep, (nbytes) / OPSIZ);             \
 140       else                                                                    \
 141         _wordcopy_bwd_dest_aligned (dst_ep, src_ep, (nbytes) / OPSIZ);        \
 142       src_ep -= (nbytes) & -OPSIZ;                                            \
 143       dst_ep -= (nbytes) & -OPSIZ;                                            \
 144       (nbytes_left) = (nbytes) % OPSIZ;                                       \
 145     } while (0)
 146
 147
 148 /* Threshold value for when to enter the unrolled loops.  */
 149 #define OP_T_THRES      16
 150
 151 #endif /* memcopy.h */