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203 lines
7.6 KiB
C
203 lines
7.6 KiB
C
/* memcopy.h -- definitions for memory copy functions. Generic C version.
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Copyright (C) 1991-2019 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Torbjorn Granlund (tege@sics.se).
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef _MEMCOPY_H
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#define _MEMCOPY_H 1
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/* The strategy of the memory functions is:
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1. Copy bytes until the destination pointer is aligned.
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2. Copy words in unrolled loops. If the source and destination
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are not aligned in the same way, use word memory operations,
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but shift and merge two read words before writing.
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3. Copy the few remaining bytes.
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This is fast on processors that have at least 10 registers for
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allocation by GCC, and that can access memory at reg+const in one
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instruction.
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I made an "exhaustive" test of this memmove when I wrote it,
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exhaustive in the sense that I tried all alignment and length
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combinations, with and without overlap. */
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#include <sys/cdefs.h>
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#include <endian.h>
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#include <pagecopy.h>
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/* The macros defined in this file are:
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BYTE_COPY_FWD(dst_beg_ptr, src_beg_ptr, nbytes_to_copy)
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BYTE_COPY_BWD(dst_end_ptr, src_end_ptr, nbytes_to_copy)
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WORD_COPY_FWD(dst_beg_ptr, src_beg_ptr, nbytes_remaining, nbytes_to_copy)
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WORD_COPY_BWD(dst_end_ptr, src_end_ptr, nbytes_remaining, nbytes_to_copy)
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MERGE(old_word, sh_1, new_word, sh_2)
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[I fail to understand. I feel stupid. --roland]
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*/
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/* Type to use for aligned memory operations.
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This should normally be the biggest type supported by a single load
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and store. */
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#define op_t unsigned long int
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#define OPSIZ (sizeof(op_t))
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/* Type to use for unaligned operations. */
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typedef unsigned char byte;
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#if __BYTE_ORDER == __LITTLE_ENDIAN
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#define MERGE(w0, sh_1, w1, sh_2) (((w0) >> (sh_1)) | ((w1) << (sh_2)))
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#endif
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#if __BYTE_ORDER == __BIG_ENDIAN
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#define MERGE(w0, sh_1, w1, sh_2) (((w0) << (sh_1)) | ((w1) >> (sh_2)))
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#endif
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/* Copy exactly NBYTES bytes from SRC_BP to DST_BP,
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without any assumptions about alignment of the pointers. */
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#define BYTE_COPY_FWD(dst_bp, src_bp, nbytes) \
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do \
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{ \
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size_t __nbytes = (nbytes); \
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while (__nbytes > 0) \
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{ \
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byte __x = ((byte *) src_bp)[0]; \
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src_bp += 1; \
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__nbytes -= 1; \
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((byte *) dst_bp)[0] = __x; \
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dst_bp += 1; \
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} \
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} while (0)
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/* Copy exactly NBYTES_TO_COPY bytes from SRC_END_PTR to DST_END_PTR,
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beginning at the bytes right before the pointers and continuing towards
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smaller addresses. Don't assume anything about alignment of the
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pointers. */
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#define BYTE_COPY_BWD(dst_ep, src_ep, nbytes) \
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do \
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{ \
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size_t __nbytes = (nbytes); \
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while (__nbytes > 0) \
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{ \
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byte __x; \
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src_ep -= 1; \
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__x = ((byte *) src_ep)[0]; \
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dst_ep -= 1; \
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__nbytes -= 1; \
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((byte *) dst_ep)[0] = __x; \
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} \
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} while (0)
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/* Copy *up to* NBYTES bytes from SRC_BP to DST_BP, with
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the assumption that DST_BP is aligned on an OPSIZ multiple. If
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not all bytes could be easily copied, store remaining number of bytes
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in NBYTES_LEFT, otherwise store 0. */
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extern void _wordcopy_fwd_aligned (long int, long int, size_t)
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attribute_hidden __THROW;
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extern void _wordcopy_fwd_dest_aligned (long int, long int, size_t)
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attribute_hidden __THROW;
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#define WORD_COPY_FWD(dst_bp, src_bp, nbytes_left, nbytes) \
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do \
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{ \
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if (src_bp % OPSIZ == 0) \
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_wordcopy_fwd_aligned (dst_bp, src_bp, (nbytes) / OPSIZ); \
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else \
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_wordcopy_fwd_dest_aligned (dst_bp, src_bp, (nbytes) / OPSIZ); \
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src_bp += (nbytes) & -OPSIZ; \
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dst_bp += (nbytes) & -OPSIZ; \
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(nbytes_left) = (nbytes) % OPSIZ; \
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} while (0)
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/* Copy *up to* NBYTES_TO_COPY bytes from SRC_END_PTR to DST_END_PTR,
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beginning at the words (of type op_t) right before the pointers and
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continuing towards smaller addresses. May take advantage of that
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DST_END_PTR is aligned on an OPSIZ multiple. If not all bytes could be
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easily copied, store remaining number of bytes in NBYTES_REMAINING,
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otherwise store 0. */
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extern void _wordcopy_bwd_aligned (long int, long int, size_t)
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attribute_hidden __THROW;
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extern void _wordcopy_bwd_dest_aligned (long int, long int, size_t)
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attribute_hidden __THROW;
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#define WORD_COPY_BWD(dst_ep, src_ep, nbytes_left, nbytes) \
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do \
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{ \
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if (src_ep % OPSIZ == 0) \
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_wordcopy_bwd_aligned (dst_ep, src_ep, (nbytes) / OPSIZ); \
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else \
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_wordcopy_bwd_dest_aligned (dst_ep, src_ep, (nbytes) / OPSIZ); \
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src_ep -= (nbytes) & -OPSIZ; \
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dst_ep -= (nbytes) & -OPSIZ; \
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(nbytes_left) = (nbytes) % OPSIZ; \
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} while (0)
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/* The macro PAGE_COPY_FWD_MAYBE (dstp, srcp, nbytes_left, nbytes) is invoked
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like WORD_COPY_FWD et al. The pointers should be at least word aligned.
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This will check if virtual copying by pages can and should be done and do it
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if so. The pointers will be aligned to PAGE_SIZE bytes. The macro requires
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that pagecopy.h defines at least PAGE_COPY_THRESHOLD to 0. If
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PAGE_COPY_THRESHOLD is non-zero, the header must also define PAGE_COPY_FWD
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and PAGE_SIZE.
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*/
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#if PAGE_COPY_THRESHOLD
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# include <assert.h>
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# define PAGE_COPY_FWD_MAYBE(dstp, srcp, nbytes_left, nbytes) \
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do \
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{ \
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if ((nbytes) >= PAGE_COPY_THRESHOLD && \
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PAGE_OFFSET ((dstp) - (srcp)) == 0) \
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{ \
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/* The amount to copy is past the threshold for copying \
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pages virtually with kernel VM operations, and the \
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source and destination addresses have the same alignment. */ \
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size_t nbytes_before = PAGE_OFFSET (-(dstp)); \
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if (nbytes_before != 0) \
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{ \
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/* First copy the words before the first page boundary. */ \
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WORD_COPY_FWD (dstp, srcp, nbytes_left, nbytes_before); \
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assert (nbytes_left == 0); \
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nbytes -= nbytes_before; \
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} \
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PAGE_COPY_FWD (dstp, srcp, nbytes_left, nbytes); \
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} \
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} while (0)
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/* The page size is always a power of two, so we can avoid modulo division. */
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# define PAGE_OFFSET(n) ((n) & (PAGE_SIZE - 1))
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#else
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# define PAGE_COPY_FWD_MAYBE(dstp, srcp, nbytes_left, nbytes) /* nada */
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#endif
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/* Threshold value for when to enter the unrolled loops. */
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#define OP_T_THRES 16
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/* Set to 1 if memcpy is safe to use for forward-copying memmove with
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overlapping addresses. This is 0 by default because memcpy implementations
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are generally not safe for overlapping addresses. */
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#define MEMCPY_OK_FOR_FWD_MEMMOVE 0
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#endif /* memcopy.h */
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