1 /* memcopy.h -- definitions for memory copy functions. Generic C version. 2 Copyright (C) 1991-2021 Free Software Foundation, Inc. 3 This file is part of the GNU C Library. 4 5 The GNU C Library is free software; you can redistribute it and/or 6 modify it under the terms of the GNU Lesser General Public 7 License as published by the Free Software Foundation; either 8 version 2.1 of the License, or (at your option) any later version. 9 10 The GNU C Library is distributed in the hope that it will be useful, 11 but WITHOUT ANY WARRANTY; without even the implied warranty of 12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 13 Lesser General Public License for more details. 14 15 You should have received a copy of the GNU Lesser General Public 16 License along with the GNU C Library; if not, see 17 <https://www.gnu.org/licenses/>. */ 18 19 #ifndef _MEMCOPY_H 20 #define _MEMCOPY_H 1 21 22 /* The strategy of the memory functions is: 23 24 1. Copy bytes until the destination pointer is aligned. 25 26 2. Copy words in unrolled loops. If the source and destination 27 are not aligned in the same way, use word memory operations, 28 but shift and merge two read words before writing. 29 30 3. Copy the few remaining bytes. 31 32 This is fast on processors that have at least 10 registers for 33 allocation by GCC, and that can access memory at reg+const in one 34 instruction. 35 36 I made an "exhaustive" test of this memmove when I wrote it, 37 exhaustive in the sense that I tried all alignment and length 38 combinations, with and without overlap. */ 39 40 #include <sys/cdefs.h> 41 #include <endian.h> 42 #include <pagecopy.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) 114 attribute_hidden __THROW; 115 extern void _wordcopy_fwd_dest_aligned (long int, long int, size_t) 116 attribute_hidden __THROW; 117 #define WORD_COPY_FWD(dst_bp, src_bp, nbytes_left, nbytes) \ 118 do \ 119 { \ 120 if (src_bp % OPSIZ == 0) \ 121 _wordcopy_fwd_aligned (dst_bp, src_bp, (nbytes) / OPSIZ); \ 122 else \ 123 _wordcopy_fwd_dest_aligned (dst_bp, src_bp, (nbytes) / OPSIZ); \ 124 src_bp += (nbytes) & -OPSIZ; \ 125 dst_bp += (nbytes) & -OPSIZ; \ 126 (nbytes_left) = (nbytes) % OPSIZ; \ 127 } while (0) 128 129 /* Copy *up to* NBYTES_TO_COPY bytes from SRC_END_PTR to DST_END_PTR, 130 beginning at the words (of type op_t) right before the pointers and 131 continuing towards smaller addresses. May take advantage of that 132 DST_END_PTR is aligned on an OPSIZ multiple. If not all bytes could be 133 easily copied, store remaining number of bytes in NBYTES_REMAINING, 134 otherwise store 0. */ 135 extern void _wordcopy_bwd_aligned (long int, long int, size_t) 136 attribute_hidden __THROW; 137 extern void _wordcopy_bwd_dest_aligned (long int, long int, size_t) 138 attribute_hidden __THROW; 139 #define WORD_COPY_BWD(dst_ep, src_ep, nbytes_left, nbytes) \ 140 do \ 141 { \ 142 if (src_ep % OPSIZ == 0) \ 143 _wordcopy_bwd_aligned (dst_ep, src_ep, (nbytes) / OPSIZ); \ 144 else \ 145 _wordcopy_bwd_dest_aligned (dst_ep, src_ep, (nbytes) / OPSIZ); \ 146 src_ep -= (nbytes) & -OPSIZ; \ 147 dst_ep -= (nbytes) & -OPSIZ; \ 148 (nbytes_left) = (nbytes) % OPSIZ; \ 149 } while (0) 150 151 /* The macro PAGE_COPY_FWD_MAYBE (dstp, srcp, nbytes_left, nbytes) is invoked 152 like WORD_COPY_FWD et al. The pointers should be at least word aligned. 153 This will check if virtual copying by pages can and should be done and do it 154 if so. The pointers will be aligned to PAGE_SIZE bytes. The macro requires 155 that pagecopy.h defines at least PAGE_COPY_THRESHOLD to 0. If 156 PAGE_COPY_THRESHOLD is non-zero, the header must also define PAGE_COPY_FWD 157 and PAGE_SIZE. 158 */ 159 #if PAGE_COPY_THRESHOLD 160 161 # include <assert.h> 162 163 # define PAGE_COPY_FWD_MAYBE(dstp, srcp, nbytes_left, nbytes) \ 164 do \ 165 { \ 166 if ((nbytes) >= PAGE_COPY_THRESHOLD \ 167 && PAGE_OFFSET ((dstp) - (srcp)) == 0) \ 168 { \ 169 /* The amount to copy is past the threshold for copying \ 170 pages virtually with kernel VM operations, and the \ 171 source and destination addresses have the same alignment. */ \ 172 size_t nbytes_before = PAGE_OFFSET (-(dstp)); \ 173 if (nbytes_before != 0) \ 174 { \ 175 /* First copy the words before the first page boundary. */ \ 176 WORD_COPY_FWD (dstp, srcp, nbytes_left, nbytes_before); \ 177 assert (nbytes_left == 0); \ 178 nbytes -= nbytes_before; \ 179 } \ 180 PAGE_COPY_FWD (dstp, srcp, nbytes_left, nbytes); \ 181 } \ 182 } while (0) 183 184 /* The page size is always a power of two, so we can avoid modulo division. */ 185 # define PAGE_OFFSET(n) ((n) & (PAGE_SIZE - 1)) 186 187 #else 188 189 # define PAGE_COPY_FWD_MAYBE(dstp, srcp, nbytes_left, nbytes) /* nada */ 190 191 #endif 192 193 /* Threshold value for when to enter the unrolled loops. */ 194 #define OP_T_THRES 16 195 196 /* Set to 1 if memcpy is safe to use for forward-copying memmove with 197 overlapping addresses. This is 0 by default because memcpy implementations 198 are generally not safe for overlapping addresses. */ 199 #define MEMCPY_OK_FOR_FWD_MEMMOVE 0 200 201 #endif /* memcopy.h */ 202