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 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 <https://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. */
66typedef 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. */
114extern void _wordcopy_fwd_aligned (long int, long int, size_t)
115 attribute_hidden __THROW;
116extern void _wordcopy_fwd_dest_aligned (long int, long int, size_t)
117 attribute_hidden __THROW;
118#define WORD_COPY_FWD(dst_bp, src_bp, nbytes_left, nbytes) \
119 do \
120 { \
121 if (src_bp % OPSIZ == 0) \
122 _wordcopy_fwd_aligned (dst_bp, src_bp, (nbytes) / OPSIZ); \
123 else \
124 _wordcopy_fwd_dest_aligned (dst_bp, src_bp, (nbytes) / OPSIZ); \
125 src_bp += (nbytes) & -OPSIZ; \
126 dst_bp += (nbytes) & -OPSIZ; \
127 (nbytes_left) = (nbytes) % OPSIZ; \
128 } while (0)
129
130/* Copy *up to* NBYTES_TO_COPY bytes from SRC_END_PTR to DST_END_PTR,
131 beginning at the words (of type op_t) right before the pointers and
132 continuing towards smaller addresses. May take advantage of that
133 DST_END_PTR is aligned on an OPSIZ multiple. If not all bytes could be
134 easily copied, store remaining number of bytes in NBYTES_REMAINING,
135 otherwise store 0. */
136extern void _wordcopy_bwd_aligned (long int, long int, size_t)
137 attribute_hidden __THROW;
138extern void _wordcopy_bwd_dest_aligned (long int, long int, size_t)
139 attribute_hidden __THROW;
140#define WORD_COPY_BWD(dst_ep, src_ep, nbytes_left, nbytes) \
141 do \
142 { \
143 if (src_ep % OPSIZ == 0) \
144 _wordcopy_bwd_aligned (dst_ep, src_ep, (nbytes) / OPSIZ); \
145 else \
146 _wordcopy_bwd_dest_aligned (dst_ep, src_ep, (nbytes) / OPSIZ); \
147 src_ep -= (nbytes) & -OPSIZ; \
148 dst_ep -= (nbytes) & -OPSIZ; \
149 (nbytes_left) = (nbytes) % OPSIZ; \
150 } while (0)
151
152/* The macro PAGE_COPY_FWD_MAYBE (dstp, srcp, nbytes_left, nbytes) is invoked
153 like WORD_COPY_FWD et al. The pointers should be at least word aligned.
154 This will check if virtual copying by pages can and should be done and do it
155 if so. The pointers will be aligned to PAGE_SIZE bytes. The macro requires
156 that pagecopy.h defines at least PAGE_COPY_THRESHOLD to 0. If
157 PAGE_COPY_THRESHOLD is non-zero, the header must also define PAGE_COPY_FWD
158 and PAGE_SIZE.
159*/
160#if PAGE_COPY_THRESHOLD
161
162# include <assert.h>
163
164# define PAGE_COPY_FWD_MAYBE(dstp, srcp, nbytes_left, nbytes) \
165 do \
166 { \
167 if ((nbytes) >= PAGE_COPY_THRESHOLD \
168 && PAGE_OFFSET ((dstp) - (srcp)) == 0) \
169 { \
170 /* The amount to copy is past the threshold for copying \
171 pages virtually with kernel VM operations, and the \
172 source and destination addresses have the same alignment. */ \
173 size_t nbytes_before = PAGE_OFFSET (-(dstp)); \
174 if (nbytes_before != 0) \
175 { \
176 /* First copy the words before the first page boundary. */ \
177 WORD_COPY_FWD (dstp, srcp, nbytes_left, nbytes_before); \
178 assert (nbytes_left == 0); \
179 nbytes -= nbytes_before; \
180 } \
181 PAGE_COPY_FWD (dstp, srcp, nbytes_left, nbytes); \
182 } \
183 } while (0)
184
185/* The page size is always a power of two, so we can avoid modulo division. */
186# define PAGE_OFFSET(n) ((n) & (PAGE_SIZE - 1))
187
188#else
189
190# define PAGE_COPY_FWD_MAYBE(dstp, srcp, nbytes_left, nbytes) /* nada */
191
192#endif
193
194/* Threshold value for when to enter the unrolled loops. */
195#define OP_T_THRES 16
196
197/* Set to 1 if memcpy is safe to use for forward-copying memmove with
198 overlapping addresses. This is 0 by default because memcpy implementations
199 are generally not safe for overlapping addresses. */
200#define MEMCPY_OK_FOR_FWD_MEMMOVE 0
201
202#endif /* memcopy.h */
203