sysdeps/generic/memcopy.h

   1 /* memcopy.h -- definitions for memory copy functions.  Generic C version.
   2    Copyright (C) 1991, 1992, 1993, 1997, 2004 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, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 /* The strategy of the memory functions is:
  22
  23      1. Copy bytes until the destination pointer is aligned.
  24
  25      2. Copy words in unrolled loops.  If the source and destination
  26      are not aligned in the same way, use word memory operations,
  27      but shift and merge two read words before writing.
  28
  29      3. Copy the few remaining bytes.
  30
  31    This is fast on processors that have at least 10 registers for
  32    allocation by GCC, and that can access memory at reg+const in one
  33    instruction.
  34
  35    I made an "exhaustive" test of this memmove when I wrote it,
  36    exhaustive in the sense that I tried all alignment and length
  37    combinations, with and without overlap.  */
  38
  39 #include <sys/cdefs.h>
  40 #include <endian.h>
  41
  42 /* The macros defined in this file are:
  43
  44    BYTE_COPY_FWD(dst_beg_ptr, src_beg_ptr, nbytes_to_copy)
  45
  46    BYTE_COPY_BWD(dst_end_ptr, src_end_ptr, nbytes_to_copy)
  47
  48    WORD_COPY_FWD(dst_beg_ptr, src_beg_ptr, nbytes_remaining, nbytes_to_copy)
  49
  50    WORD_COPY_BWD(dst_end_ptr, src_end_ptr, nbytes_remaining, nbytes_to_copy)
  51
  52    MERGE(old_word, sh_1, new_word, sh_2)
  53      [I fail to understand.  I feel stupid.  --roland]
  54 */
  55
  56 /* Type to use for aligned memory operations.
  57    This should normally be the biggest type supported by a single load
  58    and store.  */
  59 #define op_t    unsigned long int
  60 #define OPSIZ   (sizeof(op_t))
  61
  62 /* Type to use for unaligned operations.  */
  63 typedef unsigned char byte;
  64
  65 /* Optimal type for storing bytes in registers.  */
  66 #define reg_char        char
  67
  68 #if __BYTE_ORDER == __LITTLE_ENDIAN
  69 #define MERGE(w0, sh_1, w1, sh_2) (((w0) >> (sh_1)) | ((w1) << (sh_2)))
  70 #endif
  71 #if __BYTE_ORDER == __BIG_ENDIAN
  72 #define MERGE(w0, sh_1, w1, sh_2) (((w0) << (sh_1)) | ((w1) >> (sh_2)))
  73 #endif
  74
  75 /* Copy exactly NBYTES bytes from SRC_BP to DST_BP,
  76    without any assumptions about alignment of the pointers.  */
  77 #define BYTE_COPY_FWD(dst_bp, src_bp, nbytes)                                 \
  78   do                                                                          \
  79     {                                                                         \
  80       size_t __nbytes = (nbytes);                                             \
  81       while (__nbytes > 0)                                                    \
  82         {                                                                     \
  83           byte __x = ((byte *) src_bp)[0];                                    \
  84           src_bp += 1;                                                        \
  85           __nbytes -= 1;                                                      \
  86           ((byte *) dst_bp)[0] = __x;                                         \
  87           dst_bp += 1;                                                        \
  88         }                                                                     \
  89     } while (0)
  90
  91 /* Copy exactly NBYTES_TO_COPY bytes from SRC_END_PTR to DST_END_PTR,
  92    beginning at the bytes right before the pointers and continuing towards
  93    smaller addresses.  Don't assume anything about alignment of the
  94    pointers.  */
  95 #define BYTE_COPY_BWD(dst_ep, src_ep, nbytes)                                 \
  96   do                                                                          \
  97     {                                                                         \
  98       size_t __nbytes = (nbytes);                                             \
  99       while (__nbytes > 0)                                                    \
 100         {                                                                     \
 101           byte __x;                                                           \
 102           src_ep -= 1;                                                        \
 103           __x = ((byte *) src_ep)[0];                                         \
 104           dst_ep -= 1;                                                        \
 105           __nbytes -= 1;                                                      \
 106           ((byte *) dst_ep)[0] = __x;                                         \
 107         }                                                                     \
 108     } while (0)
 109
 110 /* Copy *up to* NBYTES bytes from SRC_BP to DST_BP, with
 111    the assumption that DST_BP is aligned on an OPSIZ multiple.  If
 112    not all bytes could be easily copied, store remaining number of bytes
 113    in NBYTES_LEFT, otherwise store 0.  */
 114 extern void _wordcopy_fwd_aligned (long int, long int, size_t) __THROW;
 115 extern void _wordcopy_fwd_dest_aligned (long int, long int, size_t) __THROW;
 116 #define WORD_COPY_FWD(dst_bp, src_bp, nbytes_left, nbytes)                    \
 117   do                                                                          \
 118     {                                                                         \
 119       if (src_bp % OPSIZ == 0)                                                \
 120         _wordcopy_fwd_aligned (dst_bp, src_bp, (nbytes) / OPSIZ);             \
 121       else                                                                    \
 122         _wordcopy_fwd_dest_aligned (dst_bp, src_bp, (nbytes) / OPSIZ);        \
 123       src_bp += (nbytes) & -OPSIZ;                                            \
 124       dst_bp += (nbytes) & -OPSIZ;                                            \
 125       (nbytes_left) = (nbytes) % OPSIZ;                                       \
 126     } while (0)
 127
 128 /* Copy *up to* NBYTES_TO_COPY bytes from SRC_END_PTR to DST_END_PTR,
 129    beginning at the words (of type op_t) right before the pointers and
 130    continuing towards smaller addresses.  May take advantage of that
 131    DST_END_PTR is aligned on an OPSIZ multiple.  If not all bytes could be
 132    easily copied, store remaining number of bytes in NBYTES_REMAINING,
 133    otherwise store 0.  */
 134 extern void _wordcopy_bwd_aligned (long int, long int, size_t) __THROW;
 135 extern void _wordcopy_bwd_dest_aligned (long int, long int, size_t) __THROW;
 136 #define WORD_COPY_BWD(dst_ep, src_ep, nbytes_left, nbytes)                    \
 137   do                                                                          \
 138     {                                                                         \
 139       if (src_ep % OPSIZ == 0)                                                \
 140         _wordcopy_bwd_aligned (dst_ep, src_ep, (nbytes) / OPSIZ);             \
 141       else                                                                    \
 142         _wordcopy_bwd_dest_aligned (dst_ep, src_ep, (nbytes) / OPSIZ);        \
 143       src_ep -= (nbytes) & -OPSIZ;                                            \
 144       dst_ep -= (nbytes) & -OPSIZ;                                            \
 145       (nbytes_left) = (nbytes) % OPSIZ;                                       \
 146     } while (0)
 147
 148
 149 /* Threshold value for when to enter the unrolled loops.  */
 150 #define OP_T_THRES      16