sysdeps/generic/memcopy.h

   1 /* memcopy.h -- definitions for memory copy functions.  Generic C version.
   2    Copyright (C) 1991-2015 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 #include <pagecopy.h>
  44
  45 /* The macros defined in this file are:
  46
  47    BYTE_COPY_FWD(dst_beg_ptr, src_beg_ptr, nbytes_to_copy)
  48
  49    BYTE_COPY_BWD(dst_end_ptr, src_end_ptr, nbytes_to_copy)
  50
  51    WORD_COPY_FWD(dst_beg_ptr, src_beg_ptr, nbytes_remaining, nbytes_to_copy)
  52
  53    WORD_COPY_BWD(dst_end_ptr, src_end_ptr, nbytes_remaining, nbytes_to_copy)
  54
  55    MERGE(old_word, sh_1, new_word, sh_2)
  56      [I fail to understand.  I feel stupid.  --roland]
  57 */
  58
  59 /* Type to use for aligned memory operations.
  60    This should normally be the biggest type supported by a single load
  61    and store.  */
  62 #define op_t    unsigned long int
  63 #define OPSIZ   (sizeof(op_t))
  64
  65 /* Type to use for unaligned operations.  */
  66 typedef unsigned char byte;
  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 /* The macro PAGE_COPY_FWD_MAYBE (dstp, srcp, nbytes_left, nbytes) is invoked
 149    like WORD_COPY_FWD et al.  The pointers should be at least word aligned.
 150    This will check if virtual copying by pages can and should be done and do it
 151    if so.  The pointers will be aligned to PAGE_SIZE bytes.  The macro requires
 152    that pagecopy.h defines at least PAGE_COPY_THRESHOLD to 0.  If
 153    PAGE_COPY_THRESHOLD is non-zero, the header must also define PAGE_COPY_FWD
 154    and PAGE_SIZE.
 155 */
 156 #if PAGE_COPY_THRESHOLD
 157
 158 # include <assert.h>
 159
 160 # define PAGE_COPY_FWD_MAYBE(dstp, srcp, nbytes_left, nbytes)                 \
 161   do                                                                          \
 162     {                                                                         \
 163       if ((nbytes) >= PAGE_COPY_THRESHOLD &&                                  \
 164           PAGE_OFFSET ((dstp) - (srcp)) == 0)                                 \
 165         {                                                                     \
 166           /* The amount to copy is past the threshold for copying             \
 167              pages virtually with kernel VM operations, and the               \
 168              source and destination addresses have the same alignment.  */    \
 169           size_t nbytes_before = PAGE_OFFSET (-(dstp));                       \
 170           if (nbytes_before != 0)                                             \
 171             {                                                                 \
 172               /* First copy the words before the first page boundary.  */     \
 173               WORD_COPY_FWD (dstp, srcp, nbytes_left, nbytes_before);         \
 174               assert (nbytes_left == 0);                                      \
 175               nbytes -= nbytes_before;                                        \
 176             }                                                                 \
 177           PAGE_COPY_FWD (dstp, srcp, nbytes_left, nbytes);                    \
 178         }                                                                     \
 179     } while (0)
 180
 181 /* The page size is always a power of two, so we can avoid modulo division.  */
 182 # define PAGE_OFFSET(n) ((n) & (PAGE_SIZE - 1))
 183
 184 #else
 185
 186 # define PAGE_COPY_FWD_MAYBE(dstp, srcp, nbytes_left, nbytes) /* nada */
 187
 188 #endif
 189
 190 /* Threshold value for when to enter the unrolled loops.  */
 191 #define OP_T_THRES      16
 192
 193 /* Set to 1 if memcpy is safe to use for forward-copying memmove with
 194    overlapping addresses.  This is 0 by default because memcpy implementations
 195    are generally not safe for overlapping addresses.  */
 196 #define MEMCPY_OK_FOR_FWD_MEMMOVE 0
 197
 198 #endif /* memcopy.h */