1/* memcopy.h -- definitions for memory copy functions. Generic C version.
2 Copyright (C) 1991-2023 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. */
65typedef 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. */
113extern void _wordcopy_fwd_aligned (long int, long int, size_t)
114 attribute_hidden __THROW;
115extern 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. */
135extern void _wordcopy_bwd_aligned (long int, long int, size_t)
136 attribute_hidden __THROW;
137extern 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