1 /*
2 * Oct 15, 2000 Matt Domsch <Matt_Domsch@dell.com>
3 * Nicer crc32 functions/docs submitted by linux@horizon.com. Thanks!
4 * Code was from the public domain, copyright abandoned. Code was
5 * subsequently included in the kernel, thus was re-licensed under the
6 * GNU GPL v2.
7 *
8 * Oct 12, 2000 Matt Domsch <Matt_Domsch@dell.com>
9 * Same crc32 function was used in 5 other places in the kernel.
10 * I made one version, and deleted the others.
11 * There are various incantations of crc32(). Some use a seed of 0 or ~0.
12 * Some xor at the end with ~0. The generic crc32() function takes
13 * seed as an argument, and doesn't xor at the end. Then individual
14 * users can do whatever they need.
15 * drivers/net/smc9194.c uses seed ~0, doesn't xor with ~0.
16 * fs/jffs2 uses seed 0, doesn't xor with ~0.
17 * fs/partitions/efi.c uses seed ~0, xor's with ~0.
18 *
19 * This source code is licensed under the GNU General Public License,
20 * Version 2. See the file COPYING for more details.
21 */
22
23 #include <linux/crc32.h>
24 #include <linux/kernel.h>
25 #include <linux/module.h>
26 #include <linux/compiler.h>
27 #include <linux/types.h>
28 #include <linux/slab.h>
29 #include <linux/init.h>
30 #include <asm/atomic.h>
31 #include "crc32defs.h"
32 #if CRC_LE_BITS == 8
33 #define tole(x) __constant_cpu_to_le32(x)
34 #define tobe(x) __constant_cpu_to_be32(x)
35 #else
36 #define tole(x) (x)
37 #define tobe(x) (x)
38 #endif
39 #include "crc32table.h"
40
41 MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
42 MODULE_DESCRIPTION("Ethernet CRC32 calculations");
43 MODULE_LICENSE("GPL");
44
45 /**
46 * crc32_le() - Calculate bitwise little-endian Ethernet AUTODIN II CRC32
47 * @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for
48 * other uses, or the previous crc32 value if computing incrementally.
49 * @p: pointer to buffer over which CRC is run
50 * @len: length of buffer @p
51 */
52 u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len);
53
54 #if CRC_LE_BITS == 1
55 /*
56 * In fact, the table-based code will work in this case, but it can be
57 * simplified by inlining the table in ?: form.
58 */
59
crc32_le(u32 crc,unsigned char const * p,size_t len)60 u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
61 {
62 int i;
63 while (len--) {
64 crc ^= *p++;
65 for (i = 0; i < 8; i++)
66 crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0);
67 }
68 return crc;
69 }
70 #else /* Table-based approach */
71
crc32_le(u32 crc,unsigned char const * p,size_t len)72 u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
73 {
74 # if CRC_LE_BITS == 8
75 const u32 *b =(u32 *)p;
76 const u32 *tab = crc32table_le;
77
78 # ifdef __LITTLE_ENDIAN
79 # define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8)
80 # else
81 # define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8)
82 # endif
83
84 crc = __cpu_to_le32(crc);
85 /* Align it */
86 if(unlikely(((long)b)&3 && len)){
87 do {
88 u8 *p = (u8 *)b;
89 DO_CRC(*p++);
90 b = (void *)p;
91 } while ((--len) && ((long)b)&3 );
92 }
93 if(likely(len >= 4)){
94 /* load data 32 bits wide, xor data 32 bits wide. */
95 size_t save_len = len & 3;
96 len = len >> 2;
97 --b; /* use pre increment below(*++b) for speed */
98 do {
99 crc ^= *++b;
100 DO_CRC(0);
101 DO_CRC(0);
102 DO_CRC(0);
103 DO_CRC(0);
104 } while (--len);
105 b++; /* point to next byte(s) */
106 len = save_len;
107 }
108 /* And the last few bytes */
109 if(len){
110 do {
111 u8 *p = (u8 *)b;
112 DO_CRC(*p++);
113 b = (void *)p;
114 } while (--len);
115 }
116
117 return __le32_to_cpu(crc);
118 #undef ENDIAN_SHIFT
119 #undef DO_CRC
120
121 # elif CRC_LE_BITS == 4
122 while (len--) {
123 crc ^= *p++;
124 crc = (crc >> 4) ^ crc32table_le[crc & 15];
125 crc = (crc >> 4) ^ crc32table_le[crc & 15];
126 }
127 return crc;
128 # elif CRC_LE_BITS == 2
129 while (len--) {
130 crc ^= *p++;
131 crc = (crc >> 2) ^ crc32table_le[crc & 3];
132 crc = (crc >> 2) ^ crc32table_le[crc & 3];
133 crc = (crc >> 2) ^ crc32table_le[crc & 3];
134 crc = (crc >> 2) ^ crc32table_le[crc & 3];
135 }
136 return crc;
137 # endif
138 }
139 #endif
140
141 /**
142 * crc32_be() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
143 * @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for
144 * other uses, or the previous crc32 value if computing incrementally.
145 * @p: pointer to buffer over which CRC is run
146 * @len: length of buffer @p
147 */
148 u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len);
149
150 #if CRC_BE_BITS == 1
151 /*
152 * In fact, the table-based code will work in this case, but it can be
153 * simplified by inlining the table in ?: form.
154 */
155
crc32_be(u32 crc,unsigned char const * p,size_t len)156 u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
157 {
158 int i;
159 while (len--) {
160 crc ^= *p++ << 24;
161 for (i = 0; i < 8; i++)
162 crc =
163 (crc << 1) ^ ((crc & 0x80000000) ? CRCPOLY_BE :
164 0);
165 }
166 return crc;
167 }
168
169 #else /* Table-based approach */
crc32_be(u32 crc,unsigned char const * p,size_t len)170 u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
171 {
172 # if CRC_BE_BITS == 8
173 const u32 *b =(u32 *)p;
174 const u32 *tab = crc32table_be;
175
176 # ifdef __LITTLE_ENDIAN
177 # define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8)
178 # else
179 # define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8)
180 # endif
181
182 crc = __cpu_to_be32(crc);
183 /* Align it */
184 if(unlikely(((long)b)&3 && len)){
185 do {
186 u8 *p = (u8 *)b;
187 DO_CRC(*p++);
188 b = (u32 *)p;
189 } while ((--len) && ((long)b)&3 );
190 }
191 if(likely(len >= 4)){
192 /* load data 32 bits wide, xor data 32 bits wide. */
193 size_t save_len = len & 3;
194 len = len >> 2;
195 --b; /* use pre increment below(*++b) for speed */
196 do {
197 crc ^= *++b;
198 DO_CRC(0);
199 DO_CRC(0);
200 DO_CRC(0);
201 DO_CRC(0);
202 } while (--len);
203 b++; /* point to next byte(s) */
204 len = save_len;
205 }
206 /* And the last few bytes */
207 if(len){
208 do {
209 u8 *p = (u8 *)b;
210 DO_CRC(*p++);
211 b = (void *)p;
212 } while (--len);
213 }
214 return __be32_to_cpu(crc);
215 #undef ENDIAN_SHIFT
216 #undef DO_CRC
217
218 # elif CRC_BE_BITS == 4
219 while (len--) {
220 crc ^= *p++ << 24;
221 crc = (crc << 4) ^ crc32table_be[crc >> 28];
222 crc = (crc << 4) ^ crc32table_be[crc >> 28];
223 }
224 return crc;
225 # elif CRC_BE_BITS == 2
226 while (len--) {
227 crc ^= *p++ << 24;
228 crc = (crc << 2) ^ crc32table_be[crc >> 30];
229 crc = (crc << 2) ^ crc32table_be[crc >> 30];
230 crc = (crc << 2) ^ crc32table_be[crc >> 30];
231 crc = (crc << 2) ^ crc32table_be[crc >> 30];
232 }
233 return crc;
234 # endif
235 }
236 #endif
237
238 EXPORT_SYMBOL(crc32_le);
239 EXPORT_SYMBOL(crc32_be);
240
241 /*
242 * A brief CRC tutorial.
243 *
244 * A CRC is a long-division remainder. You add the CRC to the message,
245 * and the whole thing (message+CRC) is a multiple of the given
246 * CRC polynomial. To check the CRC, you can either check that the
247 * CRC matches the recomputed value, *or* you can check that the
248 * remainder computed on the message+CRC is 0. This latter approach
249 * is used by a lot of hardware implementations, and is why so many
250 * protocols put the end-of-frame flag after the CRC.
251 *
252 * It's actually the same long division you learned in school, except that
253 * - We're working in binary, so the digits are only 0 and 1, and
254 * - When dividing polynomials, there are no carries. Rather than add and
255 * subtract, we just xor. Thus, we tend to get a bit sloppy about
256 * the difference between adding and subtracting.
257 *
258 * A 32-bit CRC polynomial is actually 33 bits long. But since it's
259 * 33 bits long, bit 32 is always going to be set, so usually the CRC
260 * is written in hex with the most significant bit omitted. (If you're
261 * familiar with the IEEE 754 floating-point format, it's the same idea.)
262 *
263 * Note that a CRC is computed over a string of *bits*, so you have
264 * to decide on the endianness of the bits within each byte. To get
265 * the best error-detecting properties, this should correspond to the
266 * order they're actually sent. For example, standard RS-232 serial is
267 * little-endian; the most significant bit (sometimes used for parity)
268 * is sent last. And when appending a CRC word to a message, you should
269 * do it in the right order, matching the endianness.
270 *
271 * Just like with ordinary division, the remainder is always smaller than
272 * the divisor (the CRC polynomial) you're dividing by. Each step of the
273 * division, you take one more digit (bit) of the dividend and append it
274 * to the current remainder. Then you figure out the appropriate multiple
275 * of the divisor to subtract to being the remainder back into range.
276 * In binary, it's easy - it has to be either 0 or 1, and to make the
277 * XOR cancel, it's just a copy of bit 32 of the remainder.
278 *
279 * When computing a CRC, we don't care about the quotient, so we can
280 * throw the quotient bit away, but subtract the appropriate multiple of
281 * the polynomial from the remainder and we're back to where we started,
282 * ready to process the next bit.
283 *
284 * A big-endian CRC written this way would be coded like:
285 * for (i = 0; i < input_bits; i++) {
286 * multiple = remainder & 0x80000000 ? CRCPOLY : 0;
287 * remainder = (remainder << 1 | next_input_bit()) ^ multiple;
288 * }
289 * Notice how, to get at bit 32 of the shifted remainder, we look
290 * at bit 31 of the remainder *before* shifting it.
291 *
292 * But also notice how the next_input_bit() bits we're shifting into
293 * the remainder don't actually affect any decision-making until
294 * 32 bits later. Thus, the first 32 cycles of this are pretty boring.
295 * Also, to add the CRC to a message, we need a 32-bit-long hole for it at
296 * the end, so we have to add 32 extra cycles shifting in zeros at the
297 * end of every message,
298 *
299 * So the standard trick is to rearrage merging in the next_input_bit()
300 * until the moment it's needed. Then the first 32 cycles can be precomputed,
301 * and merging in the final 32 zero bits to make room for the CRC can be
302 * skipped entirely.
303 * This changes the code to:
304 * for (i = 0; i < input_bits; i++) {
305 * remainder ^= next_input_bit() << 31;
306 * multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
307 * remainder = (remainder << 1) ^ multiple;
308 * }
309 * With this optimization, the little-endian code is simpler:
310 * for (i = 0; i < input_bits; i++) {
311 * remainder ^= next_input_bit();
312 * multiple = (remainder & 1) ? CRCPOLY : 0;
313 * remainder = (remainder >> 1) ^ multiple;
314 * }
315 *
316 * Note that the other details of endianness have been hidden in CRCPOLY
317 * (which must be bit-reversed) and next_input_bit().
318 *
319 * However, as long as next_input_bit is returning the bits in a sensible
320 * order, we can actually do the merging 8 or more bits at a time rather
321 * than one bit at a time:
322 * for (i = 0; i < input_bytes; i++) {
323 * remainder ^= next_input_byte() << 24;
324 * for (j = 0; j < 8; j++) {
325 * multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
326 * remainder = (remainder << 1) ^ multiple;
327 * }
328 * }
329 * Or in little-endian:
330 * for (i = 0; i < input_bytes; i++) {
331 * remainder ^= next_input_byte();
332 * for (j = 0; j < 8; j++) {
333 * multiple = (remainder & 1) ? CRCPOLY : 0;
334 * remainder = (remainder << 1) ^ multiple;
335 * }
336 * }
337 * If the input is a multiple of 32 bits, you can even XOR in a 32-bit
338 * word at a time and increase the inner loop count to 32.
339 *
340 * You can also mix and match the two loop styles, for example doing the
341 * bulk of a message byte-at-a-time and adding bit-at-a-time processing
342 * for any fractional bytes at the end.
343 *
344 * The only remaining optimization is to the byte-at-a-time table method.
345 * Here, rather than just shifting one bit of the remainder to decide
346 * in the correct multiple to subtract, we can shift a byte at a time.
347 * This produces a 40-bit (rather than a 33-bit) intermediate remainder,
348 * but again the multiple of the polynomial to subtract depends only on
349 * the high bits, the high 8 bits in this case.
350 *
351 * The multiple we need in that case is the low 32 bits of a 40-bit
352 * value whose high 8 bits are given, and which is a multiple of the
353 * generator polynomial. This is simply the CRC-32 of the given
354 * one-byte message.
355 *
356 * Two more details: normally, appending zero bits to a message which
357 * is already a multiple of a polynomial produces a larger multiple of that
358 * polynomial. To enable a CRC to detect this condition, it's common to
359 * invert the CRC before appending it. This makes the remainder of the
360 * message+crc come out not as zero, but some fixed non-zero value.
361 *
362 * The same problem applies to zero bits prepended to the message, and
363 * a similar solution is used. Instead of starting with a remainder of
364 * 0, an initial remainder of all ones is used. As long as you start
365 * the same way on decoding, it doesn't make a difference.
366 */
367
368 #ifdef UNITTEST
369
370 #include <stdlib.h>
371 #include <stdio.h>
372
373 #if 0 /*Not used at present */
374 static void
375 buf_dump(char const *prefix, unsigned char const *buf, size_t len)
376 {
377 fputs(prefix, stdout);
378 while (len--)
379 printf(" %02x", *buf++);
380 putchar('\n');
381
382 }
383 #endif
384
bytereverse(unsigned char * buf,size_t len)385 static void bytereverse(unsigned char *buf, size_t len)
386 {
387 while (len--) {
388 unsigned char x = bitrev8(*buf);
389 *buf++ = x;
390 }
391 }
392
random_garbage(unsigned char * buf,size_t len)393 static void random_garbage(unsigned char *buf, size_t len)
394 {
395 while (len--)
396 *buf++ = (unsigned char) random();
397 }
398
399 #if 0 /* Not used at present */
400 static void store_le(u32 x, unsigned char *buf)
401 {
402 buf[0] = (unsigned char) x;
403 buf[1] = (unsigned char) (x >> 8);
404 buf[2] = (unsigned char) (x >> 16);
405 buf[3] = (unsigned char) (x >> 24);
406 }
407 #endif
408
store_be(u32 x,unsigned char * buf)409 static void store_be(u32 x, unsigned char *buf)
410 {
411 buf[0] = (unsigned char) (x >> 24);
412 buf[1] = (unsigned char) (x >> 16);
413 buf[2] = (unsigned char) (x >> 8);
414 buf[3] = (unsigned char) x;
415 }
416
417 /*
418 * This checks that CRC(buf + CRC(buf)) = 0, and that
419 * CRC commutes with bit-reversal. This has the side effect
420 * of bytewise bit-reversing the input buffer, and returns
421 * the CRC of the reversed buffer.
422 */
test_step(u32 init,unsigned char * buf,size_t len)423 static u32 test_step(u32 init, unsigned char *buf, size_t len)
424 {
425 u32 crc1, crc2;
426 size_t i;
427
428 crc1 = crc32_be(init, buf, len);
429 store_be(crc1, buf + len);
430 crc2 = crc32_be(init, buf, len + 4);
431 if (crc2)
432 printf("\nCRC cancellation fail: 0x%08x should be 0\n",
433 crc2);
434
435 for (i = 0; i <= len + 4; i++) {
436 crc2 = crc32_be(init, buf, i);
437 crc2 = crc32_be(crc2, buf + i, len + 4 - i);
438 if (crc2)
439 printf("\nCRC split fail: 0x%08x\n", crc2);
440 }
441
442 /* Now swap it around for the other test */
443
444 bytereverse(buf, len + 4);
445 init = bitrev32(init);
446 crc2 = bitrev32(crc1);
447 if (crc1 != bitrev32(crc2))
448 printf("\nBit reversal fail: 0x%08x -> 0x%08x -> 0x%08x\n",
449 crc1, crc2, bitrev32(crc2));
450 crc1 = crc32_le(init, buf, len);
451 if (crc1 != crc2)
452 printf("\nCRC endianness fail: 0x%08x != 0x%08x\n", crc1,
453 crc2);
454 crc2 = crc32_le(init, buf, len + 4);
455 if (crc2)
456 printf("\nCRC cancellation fail: 0x%08x should be 0\n",
457 crc2);
458
459 for (i = 0; i <= len + 4; i++) {
460 crc2 = crc32_le(init, buf, i);
461 crc2 = crc32_le(crc2, buf + i, len + 4 - i);
462 if (crc2)
463 printf("\nCRC split fail: 0x%08x\n", crc2);
464 }
465
466 return crc1;
467 }
468
469 #define SIZE 64
470 #define INIT1 0
471 #define INIT2 0
472
main(void)473 int main(void)
474 {
475 unsigned char buf1[SIZE + 4];
476 unsigned char buf2[SIZE + 4];
477 unsigned char buf3[SIZE + 4];
478 int i, j;
479 u32 crc1, crc2, crc3;
480
481 for (i = 0; i <= SIZE; i++) {
482 printf("\rTesting length %d...", i);
483 fflush(stdout);
484 random_garbage(buf1, i);
485 random_garbage(buf2, i);
486 for (j = 0; j < i; j++)
487 buf3[j] = buf1[j] ^ buf2[j];
488
489 crc1 = test_step(INIT1, buf1, i);
490 crc2 = test_step(INIT2, buf2, i);
491 /* Now check that CRC(buf1 ^ buf2) = CRC(buf1) ^ CRC(buf2) */
492 crc3 = test_step(INIT1 ^ INIT2, buf3, i);
493 if (crc3 != (crc1 ^ crc2))
494 printf("CRC XOR fail: 0x%08x != 0x%08x ^ 0x%08x\n",
495 crc3, crc1, crc2);
496 }
497 printf("\nAll test complete. No failures expected.\n");
498 return 0;
499 }
500
501 #endif /* UNITTEST */
502