1 /* Copyright (C) 1991-2023 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contributed by Torbjorn Granlund (tege@sics.se).
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 #ifdef HAVE_CONFIG_H
20 # include "config.h"
21 #endif
22
23 #if defined HAVE_STRING_H || defined _LIBC
24 # include <string.h>
25 #endif
26
27 #undef memcmp
28
29 #ifndef MEMCMP
30 # define MEMCMP memcmp
31 #endif
32
33 #ifdef _LIBC
34
35 # include <memcopy.h>
36 # include <endian.h>
37
38 # if __BYTE_ORDER == __BIG_ENDIAN
39 # define WORDS_BIGENDIAN
40 # endif
41
42 #else /* Not in the GNU C library. */
43
44 # include <sys/types.h>
45
46 /* Type to use for aligned memory operations.
47 This should normally be the biggest type supported by a single load
48 and store. Must be an unsigned type. */
49 # define OPSIZ (sizeof (op_t))
50
51 /* Type to use for unaligned operations. */
52 typedef unsigned char byte;
53
54 # ifndef WORDS_BIGENDIAN
55 # define MERGE(w0, sh_1, w1, sh_2) (((w0) >> (sh_1)) | ((w1) << (sh_2)))
56 # else
57 # define MERGE(w0, sh_1, w1, sh_2) (((w0) << (sh_1)) | ((w1) >> (sh_2)))
58 # endif
59
60 #endif /* In the GNU C library. */
61
62 #ifdef WORDS_BIGENDIAN
63 # define CMP_LT_OR_GT(a, b) ((a) > (b) ? 1 : -1)
64 #else
65 # define CMP_LT_OR_GT(a, b) memcmp_bytes ((a), (b))
66 #endif
67
68 /* BE VERY CAREFUL IF YOU CHANGE THIS CODE! */
69
70 /* The strategy of this memcmp is:
71
72 1. Compare bytes until one of the block pointers is aligned.
73
74 2. Compare using memcmp_common_alignment or
75 memcmp_not_common_alignment, regarding the alignment of the other
76 block after the initial byte operations. The maximum number of
77 full words (of type op_t) are compared in this way.
78
79 3. Compare the few remaining bytes. */
80
81 #ifndef WORDS_BIGENDIAN
82 /* memcmp_bytes -- Compare A and B bytewise in the byte order of the machine.
83 A and B are known to be different.
84 This is needed only on little-endian machines. */
85
86 static int memcmp_bytes (op_t, op_t) __THROW;
87
88 static int
89 memcmp_bytes (op_t a, op_t b)
90 {
91 long int srcp1 = (long int) &a;
92 long int srcp2 = (long int) &b;
93 op_t a0, b0;
94
95 do
96 {
97 a0 = ((byte *) srcp1)[0];
98 b0 = ((byte *) srcp2)[0];
99 srcp1 += 1;
100 srcp2 += 1;
101 }
102 while (a0 == b0);
103 return a0 - b0;
104 }
105 #endif
106
107 static int memcmp_common_alignment (long, long, size_t) __THROW;
108
109 /* memcmp_common_alignment -- Compare blocks at SRCP1 and SRCP2 with LEN `op_t'
110 objects (not LEN bytes!). Both SRCP1 and SRCP2 should be aligned for
111 memory operations on `op_t's. */
112 static int
113 memcmp_common_alignment (long int srcp1, long int srcp2, size_t len)
114 {
115 op_t a0, a1;
116 op_t b0, b1;
117
118 switch (len % 4)
119 {
120 default: /* Avoid warning about uninitialized local variables. */
121 case 2:
122 a0 = ((op_t *) srcp1)[0];
123 b0 = ((op_t *) srcp2)[0];
124 srcp1 -= 2 * OPSIZ;
125 srcp2 -= 2 * OPSIZ;
126 len += 2;
127 goto do1;
128 case 3:
129 a1 = ((op_t *) srcp1)[0];
130 b1 = ((op_t *) srcp2)[0];
131 srcp1 -= OPSIZ;
132 srcp2 -= OPSIZ;
133 len += 1;
134 goto do2;
135 case 0:
136 if (OP_T_THRES <= 3 * OPSIZ && len == 0)
137 return 0;
138 a0 = ((op_t *) srcp1)[0];
139 b0 = ((op_t *) srcp2)[0];
140 goto do3;
141 case 1:
142 a1 = ((op_t *) srcp1)[0];
143 b1 = ((op_t *) srcp2)[0];
144 srcp1 += OPSIZ;
145 srcp2 += OPSIZ;
146 len -= 1;
147 if (OP_T_THRES <= 3 * OPSIZ && len == 0)
148 goto do0;
149 /* Fall through. */
150 }
151
152 do
153 {
154 a0 = ((op_t *) srcp1)[0];
155 b0 = ((op_t *) srcp2)[0];
156 if (a1 != b1)
157 return CMP_LT_OR_GT (a1, b1);
158
159 do3:
160 a1 = ((op_t *) srcp1)[1];
161 b1 = ((op_t *) srcp2)[1];
162 if (a0 != b0)
163 return CMP_LT_OR_GT (a0, b0);
164
165 do2:
166 a0 = ((op_t *) srcp1)[2];
167 b0 = ((op_t *) srcp2)[2];
168 if (a1 != b1)
169 return CMP_LT_OR_GT (a1, b1);
170
171 do1:
172 a1 = ((op_t *) srcp1)[3];
173 b1 = ((op_t *) srcp2)[3];
174 if (a0 != b0)
175 return CMP_LT_OR_GT (a0, b0);
176
177 srcp1 += 4 * OPSIZ;
178 srcp2 += 4 * OPSIZ;
179 len -= 4;
180 }
181 while (len != 0);
182
183 /* This is the right position for do0. Please don't move
184 it into the loop. */
185 do0:
186 if (a1 != b1)
187 return CMP_LT_OR_GT (a1, b1);
188 return 0;
189 }
190
191 static int memcmp_not_common_alignment (long, long, size_t) __THROW;
192
193 /* memcmp_not_common_alignment -- Compare blocks at SRCP1 and SRCP2 with LEN
194 `op_t' objects (not LEN bytes!). SRCP2 should be aligned for memory
195 operations on `op_t', but SRCP1 *should be unaligned*. */
196 static int
197 memcmp_not_common_alignment (long int srcp1, long int srcp2, size_t len)
198 {
199 op_t a0, a1, a2, a3;
200 op_t b0, b1, b2, b3;
201 op_t x;
202 int shl, shr;
203
204 /* Calculate how to shift a word read at the memory operation
205 aligned srcp1 to make it aligned for comparison. */
206
207 shl = 8 * (srcp1 % OPSIZ);
208 shr = 8 * OPSIZ - shl;
209
210 /* Make SRCP1 aligned by rounding it down to the beginning of the `op_t'
211 it points in the middle of. */
212 srcp1 &= -OPSIZ;
213
214 switch (len % 4)
215 {
216 default: /* Avoid warning about uninitialized local variables. */
217 case 2:
218 a1 = ((op_t *) srcp1)[0];
219 a2 = ((op_t *) srcp1)[1];
220 b2 = ((op_t *) srcp2)[0];
221 srcp1 -= 1 * OPSIZ;
222 srcp2 -= 2 * OPSIZ;
223 len += 2;
224 goto do1;
225 case 3:
226 a0 = ((op_t *) srcp1)[0];
227 a1 = ((op_t *) srcp1)[1];
228 b1 = ((op_t *) srcp2)[0];
229 srcp2 -= 1 * OPSIZ;
230 len += 1;
231 goto do2;
232 case 0:
233 if (OP_T_THRES <= 3 * OPSIZ && len == 0)
234 return 0;
235 a3 = ((op_t *) srcp1)[0];
236 a0 = ((op_t *) srcp1)[1];
237 b0 = ((op_t *) srcp2)[0];
238 srcp1 += 1 * OPSIZ;
239 goto do3;
240 case 1:
241 a2 = ((op_t *) srcp1)[0];
242 a3 = ((op_t *) srcp1)[1];
243 b3 = ((op_t *) srcp2)[0];
244 srcp1 += 2 * OPSIZ;
245 srcp2 += 1 * OPSIZ;
246 len -= 1;
247 if (OP_T_THRES <= 3 * OPSIZ && len == 0)
248 goto do0;
249 /* Fall through. */
250 }
251
252 do
253 {
254 a0 = ((op_t *) srcp1)[0];
255 b0 = ((op_t *) srcp2)[0];
256 x = MERGE(a2, shl, a3, shr);
257 if (x != b3)
258 return CMP_LT_OR_GT (x, b3);
259
260 do3:
261 a1 = ((op_t *) srcp1)[1];
262 b1 = ((op_t *) srcp2)[1];
263 x = MERGE(a3, shl, a0, shr);
264 if (x != b0)
265 return CMP_LT_OR_GT (x, b0);
266
267 do2:
268 a2 = ((op_t *) srcp1)[2];
269 b2 = ((op_t *) srcp2)[2];
270 x = MERGE(a0, shl, a1, shr);
271 if (x != b1)
272 return CMP_LT_OR_GT (x, b1);
273
274 do1:
275 a3 = ((op_t *) srcp1)[3];
276 b3 = ((op_t *) srcp2)[3];
277 x = MERGE(a1, shl, a2, shr);
278 if (x != b2)
279 return CMP_LT_OR_GT (x, b2);
280
281 srcp1 += 4 * OPSIZ;
282 srcp2 += 4 * OPSIZ;
283 len -= 4;
284 }
285 while (len != 0);
286
287 /* This is the right position for do0. Please don't move
288 it into the loop. */
289 do0:
290 x = MERGE(a2, shl, a3, shr);
291 if (x != b3)
292 return CMP_LT_OR_GT (x, b3);
293 return 0;
294 }
295
296 int
297 MEMCMP (const void *s1, const void *s2, size_t len)
298 {
299 op_t a0;
300 op_t b0;
301 long int srcp1 = (long int) s1;
302 long int srcp2 = (long int) s2;
303 op_t res;
304
305 if (len >= OP_T_THRES)
306 {
307 /* There are at least some bytes to compare. No need to test
308 for LEN == 0 in this alignment loop. */
309 while (srcp2 % OPSIZ != 0)
310 {
311 a0 = ((byte *) srcp1)[0];
312 b0 = ((byte *) srcp2)[0];
313 srcp1 += 1;
314 srcp2 += 1;
315 res = a0 - b0;
316 if (res != 0)
317 return res;
318 len -= 1;
319 }
320
321 /* SRCP2 is now aligned for memory operations on `op_t'.
322 SRCP1 alignment determines if we can do a simple,
323 aligned compare or need to shuffle bits. */
324
325 if (srcp1 % OPSIZ == 0)
326 res = memcmp_common_alignment (srcp1, srcp2, len / OPSIZ);
327 else
328 res = memcmp_not_common_alignment (srcp1, srcp2, len / OPSIZ);
329 if (res != 0)
330 return res;
331
332 /* Number of bytes remaining in the interval [0..OPSIZ-1]. */
333 srcp1 += len & -OPSIZ;
334 srcp2 += len & -OPSIZ;
335 len %= OPSIZ;
336 }
337
338 /* There are just a few bytes to compare. Use byte memory operations. */
339 while (len != 0)
340 {
341 a0 = ((byte *) srcp1)[0];
342 b0 = ((byte *) srcp2)[0];
343 srcp1 += 1;
344 srcp2 += 1;
345 res = a0 - b0;
346 if (res != 0)
347 return res;
348 len -= 1;
349 }
350
351 return 0;
352 }
353 libc_hidden_builtin_def(memcmp)
354 #ifdef weak_alias
355 # undef bcmp
356 weak_alias (memcmp, bcmp)
357 #endif
358
359 #undef __memcmpeq
360 strong_alias (memcmp, __memcmpeq)
361 libc_hidden_def(__memcmpeq)