1 | /* Copyright (C) 1991-2022 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 op_t unsigned long int |
50 | # define OPSIZ (sizeof (op_t)) |
51 | |
52 | /* Threshold value for when to enter the unrolled loops. */ |
53 | # define OP_T_THRES 16 |
54 | |
55 | /* Type to use for unaligned operations. */ |
56 | typedef unsigned char byte; |
57 | |
58 | # ifndef WORDS_BIGENDIAN |
59 | # define MERGE(w0, sh_1, w1, sh_2) (((w0) >> (sh_1)) | ((w1) << (sh_2))) |
60 | # else |
61 | # define MERGE(w0, sh_1, w1, sh_2) (((w0) << (sh_1)) | ((w1) >> (sh_2))) |
62 | # endif |
63 | |
64 | #endif /* In the GNU C library. */ |
65 | |
66 | #ifdef WORDS_BIGENDIAN |
67 | # define CMP_LT_OR_GT(a, b) ((a) > (b) ? 1 : -1) |
68 | #else |
69 | # define CMP_LT_OR_GT(a, b) memcmp_bytes ((a), (b)) |
70 | #endif |
71 | |
72 | /* BE VERY CAREFUL IF YOU CHANGE THIS CODE! */ |
73 | |
74 | /* The strategy of this memcmp is: |
75 | |
76 | 1. Compare bytes until one of the block pointers is aligned. |
77 | |
78 | 2. Compare using memcmp_common_alignment or |
79 | memcmp_not_common_alignment, regarding the alignment of the other |
80 | block after the initial byte operations. The maximum number of |
81 | full words (of type op_t) are compared in this way. |
82 | |
83 | 3. Compare the few remaining bytes. */ |
84 | |
85 | #ifndef WORDS_BIGENDIAN |
86 | /* memcmp_bytes -- Compare A and B bytewise in the byte order of the machine. |
87 | A and B are known to be different. |
88 | This is needed only on little-endian machines. */ |
89 | |
90 | static int memcmp_bytes (op_t, op_t) __THROW; |
91 | |
92 | static int |
93 | memcmp_bytes (op_t a, op_t b) |
94 | { |
95 | long int srcp1 = (long int) &a; |
96 | long int srcp2 = (long int) &b; |
97 | op_t a0, b0; |
98 | |
99 | do |
100 | { |
101 | a0 = ((byte *) srcp1)[0]; |
102 | b0 = ((byte *) srcp2)[0]; |
103 | srcp1 += 1; |
104 | srcp2 += 1; |
105 | } |
106 | while (a0 == b0); |
107 | return a0 - b0; |
108 | } |
109 | #endif |
110 | |
111 | static int memcmp_common_alignment (long, long, size_t) __THROW; |
112 | |
113 | /* memcmp_common_alignment -- Compare blocks at SRCP1 and SRCP2 with LEN `op_t' |
114 | objects (not LEN bytes!). Both SRCP1 and SRCP2 should be aligned for |
115 | memory operations on `op_t's. */ |
116 | static int |
117 | memcmp_common_alignment (long int srcp1, long int srcp2, size_t len) |
118 | { |
119 | op_t a0, a1; |
120 | op_t b0, b1; |
121 | |
122 | switch (len % 4) |
123 | { |
124 | default: /* Avoid warning about uninitialized local variables. */ |
125 | case 2: |
126 | a0 = ((op_t *) srcp1)[0]; |
127 | b0 = ((op_t *) srcp2)[0]; |
128 | srcp1 -= 2 * OPSIZ; |
129 | srcp2 -= 2 * OPSIZ; |
130 | len += 2; |
131 | goto do1; |
132 | case 3: |
133 | a1 = ((op_t *) srcp1)[0]; |
134 | b1 = ((op_t *) srcp2)[0]; |
135 | srcp1 -= OPSIZ; |
136 | srcp2 -= OPSIZ; |
137 | len += 1; |
138 | goto do2; |
139 | case 0: |
140 | if (OP_T_THRES <= 3 * OPSIZ && len == 0) |
141 | return 0; |
142 | a0 = ((op_t *) srcp1)[0]; |
143 | b0 = ((op_t *) srcp2)[0]; |
144 | goto do3; |
145 | case 1: |
146 | a1 = ((op_t *) srcp1)[0]; |
147 | b1 = ((op_t *) srcp2)[0]; |
148 | srcp1 += OPSIZ; |
149 | srcp2 += OPSIZ; |
150 | len -= 1; |
151 | if (OP_T_THRES <= 3 * OPSIZ && len == 0) |
152 | goto do0; |
153 | /* Fall through. */ |
154 | } |
155 | |
156 | do |
157 | { |
158 | a0 = ((op_t *) srcp1)[0]; |
159 | b0 = ((op_t *) srcp2)[0]; |
160 | if (a1 != b1) |
161 | return CMP_LT_OR_GT (a1, b1); |
162 | |
163 | do3: |
164 | a1 = ((op_t *) srcp1)[1]; |
165 | b1 = ((op_t *) srcp2)[1]; |
166 | if (a0 != b0) |
167 | return CMP_LT_OR_GT (a0, b0); |
168 | |
169 | do2: |
170 | a0 = ((op_t *) srcp1)[2]; |
171 | b0 = ((op_t *) srcp2)[2]; |
172 | if (a1 != b1) |
173 | return CMP_LT_OR_GT (a1, b1); |
174 | |
175 | do1: |
176 | a1 = ((op_t *) srcp1)[3]; |
177 | b1 = ((op_t *) srcp2)[3]; |
178 | if (a0 != b0) |
179 | return CMP_LT_OR_GT (a0, b0); |
180 | |
181 | srcp1 += 4 * OPSIZ; |
182 | srcp2 += 4 * OPSIZ; |
183 | len -= 4; |
184 | } |
185 | while (len != 0); |
186 | |
187 | /* This is the right position for do0. Please don't move |
188 | it into the loop. */ |
189 | do0: |
190 | if (a1 != b1) |
191 | return CMP_LT_OR_GT (a1, b1); |
192 | return 0; |
193 | } |
194 | |
195 | static int memcmp_not_common_alignment (long, long, size_t) __THROW; |
196 | |
197 | /* memcmp_not_common_alignment -- Compare blocks at SRCP1 and SRCP2 with LEN |
198 | `op_t' objects (not LEN bytes!). SRCP2 should be aligned for memory |
199 | operations on `op_t', but SRCP1 *should be unaligned*. */ |
200 | static int |
201 | memcmp_not_common_alignment (long int srcp1, long int srcp2, size_t len) |
202 | { |
203 | op_t a0, a1, a2, a3; |
204 | op_t b0, b1, b2, b3; |
205 | op_t x; |
206 | int shl, shr; |
207 | |
208 | /* Calculate how to shift a word read at the memory operation |
209 | aligned srcp1 to make it aligned for comparison. */ |
210 | |
211 | shl = 8 * (srcp1 % OPSIZ); |
212 | shr = 8 * OPSIZ - shl; |
213 | |
214 | /* Make SRCP1 aligned by rounding it down to the beginning of the `op_t' |
215 | it points in the middle of. */ |
216 | srcp1 &= -OPSIZ; |
217 | |
218 | switch (len % 4) |
219 | { |
220 | default: /* Avoid warning about uninitialized local variables. */ |
221 | case 2: |
222 | a1 = ((op_t *) srcp1)[0]; |
223 | a2 = ((op_t *) srcp1)[1]; |
224 | b2 = ((op_t *) srcp2)[0]; |
225 | srcp1 -= 1 * OPSIZ; |
226 | srcp2 -= 2 * OPSIZ; |
227 | len += 2; |
228 | goto do1; |
229 | case 3: |
230 | a0 = ((op_t *) srcp1)[0]; |
231 | a1 = ((op_t *) srcp1)[1]; |
232 | b1 = ((op_t *) srcp2)[0]; |
233 | srcp2 -= 1 * OPSIZ; |
234 | len += 1; |
235 | goto do2; |
236 | case 0: |
237 | if (OP_T_THRES <= 3 * OPSIZ && len == 0) |
238 | return 0; |
239 | a3 = ((op_t *) srcp1)[0]; |
240 | a0 = ((op_t *) srcp1)[1]; |
241 | b0 = ((op_t *) srcp2)[0]; |
242 | srcp1 += 1 * OPSIZ; |
243 | goto do3; |
244 | case 1: |
245 | a2 = ((op_t *) srcp1)[0]; |
246 | a3 = ((op_t *) srcp1)[1]; |
247 | b3 = ((op_t *) srcp2)[0]; |
248 | srcp1 += 2 * OPSIZ; |
249 | srcp2 += 1 * OPSIZ; |
250 | len -= 1; |
251 | if (OP_T_THRES <= 3 * OPSIZ && len == 0) |
252 | goto do0; |
253 | /* Fall through. */ |
254 | } |
255 | |
256 | do |
257 | { |
258 | a0 = ((op_t *) srcp1)[0]; |
259 | b0 = ((op_t *) srcp2)[0]; |
260 | x = MERGE(a2, shl, a3, shr); |
261 | if (x != b3) |
262 | return CMP_LT_OR_GT (x, b3); |
263 | |
264 | do3: |
265 | a1 = ((op_t *) srcp1)[1]; |
266 | b1 = ((op_t *) srcp2)[1]; |
267 | x = MERGE(a3, shl, a0, shr); |
268 | if (x != b0) |
269 | return CMP_LT_OR_GT (x, b0); |
270 | |
271 | do2: |
272 | a2 = ((op_t *) srcp1)[2]; |
273 | b2 = ((op_t *) srcp2)[2]; |
274 | x = MERGE(a0, shl, a1, shr); |
275 | if (x != b1) |
276 | return CMP_LT_OR_GT (x, b1); |
277 | |
278 | do1: |
279 | a3 = ((op_t *) srcp1)[3]; |
280 | b3 = ((op_t *) srcp2)[3]; |
281 | x = MERGE(a1, shl, a2, shr); |
282 | if (x != b2) |
283 | return CMP_LT_OR_GT (x, b2); |
284 | |
285 | srcp1 += 4 * OPSIZ; |
286 | srcp2 += 4 * OPSIZ; |
287 | len -= 4; |
288 | } |
289 | while (len != 0); |
290 | |
291 | /* This is the right position for do0. Please don't move |
292 | it into the loop. */ |
293 | do0: |
294 | x = MERGE(a2, shl, a3, shr); |
295 | if (x != b3) |
296 | return CMP_LT_OR_GT (x, b3); |
297 | return 0; |
298 | } |
299 | |
300 | int |
301 | MEMCMP (const void *s1, const void *s2, size_t len) |
302 | { |
303 | op_t a0; |
304 | op_t b0; |
305 | long int srcp1 = (long int) s1; |
306 | long int srcp2 = (long int) s2; |
307 | op_t res; |
308 | |
309 | if (len >= OP_T_THRES) |
310 | { |
311 | /* There are at least some bytes to compare. No need to test |
312 | for LEN == 0 in this alignment loop. */ |
313 | while (srcp2 % OPSIZ != 0) |
314 | { |
315 | a0 = ((byte *) srcp1)[0]; |
316 | b0 = ((byte *) srcp2)[0]; |
317 | srcp1 += 1; |
318 | srcp2 += 1; |
319 | res = a0 - b0; |
320 | if (res != 0) |
321 | return res; |
322 | len -= 1; |
323 | } |
324 | |
325 | /* SRCP2 is now aligned for memory operations on `op_t'. |
326 | SRCP1 alignment determines if we can do a simple, |
327 | aligned compare or need to shuffle bits. */ |
328 | |
329 | if (srcp1 % OPSIZ == 0) |
330 | res = memcmp_common_alignment (srcp1, srcp2, len: len / OPSIZ); |
331 | else |
332 | res = memcmp_not_common_alignment (srcp1, srcp2, len: len / OPSIZ); |
333 | if (res != 0) |
334 | return res; |
335 | |
336 | /* Number of bytes remaining in the interval [0..OPSIZ-1]. */ |
337 | srcp1 += len & -OPSIZ; |
338 | srcp2 += len & -OPSIZ; |
339 | len %= OPSIZ; |
340 | } |
341 | |
342 | /* There are just a few bytes to compare. Use byte memory operations. */ |
343 | while (len != 0) |
344 | { |
345 | a0 = ((byte *) srcp1)[0]; |
346 | b0 = ((byte *) srcp2)[0]; |
347 | srcp1 += 1; |
348 | srcp2 += 1; |
349 | res = a0 - b0; |
350 | if (res != 0) |
351 | return res; |
352 | len -= 1; |
353 | } |
354 | |
355 | return 0; |
356 | } |
357 | libc_hidden_builtin_def(memcmp) |
358 | #ifdef weak_alias |
359 | # undef bcmp |
360 | weak_alias (memcmp, bcmp) |
361 | #endif |
362 | |
363 | #undef __memcmpeq |
364 | strong_alias (memcmp, __memcmpeq) |
365 | libc_hidden_def(__memcmpeq) |
366 | |