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Kyungmin Parkf399d4a2008-11-19 16:23:06 +01001/*
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#ifdef UBI_LINUX
24#include <linux/crc32.h>
25#include <linux/kernel.h>
26#include <linux/module.h>
27#include <linux/compiler.h>
28#endif
29#include <linux/types.h>
30
31#include <asm/byteorder.h>
32
33#ifdef UBI_LINUX
34#include <linux/slab.h>
35#include <linux/init.h>
36#include <asm/atomic.h>
37#endif
38#include "crc32defs.h"
39#define CRC_LE_BITS 8
40
Kyungmin Parkf399d4a2008-11-19 16:23:06 +010041#if CRC_LE_BITS == 8
Kim Phillipseef1cf22012-10-29 13:34:23 +000042#define tole(x) cpu_to_le32(x)
43#define tobe(x) cpu_to_be32(x)
Kyungmin Parkf399d4a2008-11-19 16:23:06 +010044#else
45#define tole(x) (x)
46#define tobe(x) (x)
47#endif
48#include "crc32table.h"
49#ifdef UBI_LINUX
50MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
51MODULE_DESCRIPTION("Ethernet CRC32 calculations");
52MODULE_LICENSE("GPL");
53#endif
54/**
55 * crc32_le() - Calculate bitwise little-endian Ethernet AUTODIN II CRC32
56 * @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for
57 * other uses, or the previous crc32 value if computing incrementally.
58 * @p: pointer to buffer over which CRC is run
59 * @len: length of buffer @p
60 */
61u32 crc32_le(u32 crc, unsigned char const *p, size_t len);
62
63#if CRC_LE_BITS == 1
64/*
65 * In fact, the table-based code will work in this case, but it can be
66 * simplified by inlining the table in ?: form.
67 */
68
69u32 crc32_le(u32 crc, unsigned char const *p, size_t len)
70{
71 int i;
72 while (len--) {
73 crc ^= *p++;
74 for (i = 0; i < 8; i++)
75 crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0);
76 }
77 return crc;
78}
79#else /* Table-based approach */
80
81u32 crc32_le(u32 crc, unsigned char const *p, size_t len)
82{
83# if CRC_LE_BITS == 8
84 const u32 *b =(u32 *)p;
85 const u32 *tab = crc32table_le;
86
87# ifdef __LITTLE_ENDIAN
88# define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8)
89# else
90# define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8)
91# endif
Wolfgang Denk455ae7e2008-12-16 01:02:17 +010092 /* printf("Crc32_le crc=%x\n",crc); */
Kyungmin Parkf399d4a2008-11-19 16:23:06 +010093 crc = __cpu_to_le32(crc);
94 /* Align it */
95 if((((long)b)&3 && len)){
96 do {
97 u8 *p = (u8 *)b;
98 DO_CRC(*p++);
99 b = (void *)p;
100 } while ((--len) && ((long)b)&3 );
101 }
102 if((len >= 4)){
103 /* load data 32 bits wide, xor data 32 bits wide. */
104 size_t save_len = len & 3;
Wolfgang Denk93e14592013-10-04 17:43:24 +0200105 len = len >> 2;
Kyungmin Parkf399d4a2008-11-19 16:23:06 +0100106 --b; /* use pre increment below(*++b) for speed */
107 do {
108 crc ^= *++b;
109 DO_CRC(0);
110 DO_CRC(0);
111 DO_CRC(0);
112 DO_CRC(0);
113 } while (--len);
114 b++; /* point to next byte(s) */
115 len = save_len;
116 }
117 /* And the last few bytes */
118 if(len){
119 do {
120 u8 *p = (u8 *)b;
121 DO_CRC(*p++);
122 b = (void *)p;
123 } while (--len);
124 }
125
126 return __le32_to_cpu(crc);
127#undef ENDIAN_SHIFT
128#undef DO_CRC
129
130# elif CRC_LE_BITS == 4
131 while (len--) {
132 crc ^= *p++;
133 crc = (crc >> 4) ^ crc32table_le[crc & 15];
134 crc = (crc >> 4) ^ crc32table_le[crc & 15];
135 }
136 return crc;
137# elif CRC_LE_BITS == 2
138 while (len--) {
139 crc ^= *p++;
140 crc = (crc >> 2) ^ crc32table_le[crc & 3];
141 crc = (crc >> 2) ^ crc32table_le[crc & 3];
142 crc = (crc >> 2) ^ crc32table_le[crc & 3];
143 crc = (crc >> 2) ^ crc32table_le[crc & 3];
144 }
145 return crc;
146# endif
147}
148#endif
149#ifdef UBI_LINUX
150/**
151 * crc32_be() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
152 * @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for
153 * other uses, or the previous crc32 value if computing incrementally.
154 * @p: pointer to buffer over which CRC is run
155 * @len: length of buffer @p
156 */
157u32 __attribute_pure__ crc32_be(u32 crc, unsigned char const *p, size_t len);
158
159#if CRC_BE_BITS == 1
160/*
161 * In fact, the table-based code will work in this case, but it can be
162 * simplified by inlining the table in ?: form.
163 */
164
165u32 __attribute_pure__ crc32_be(u32 crc, unsigned char const *p, size_t len)
166{
167 int i;
168 while (len--) {
169 crc ^= *p++ << 24;
170 for (i = 0; i < 8; i++)
171 crc =
172 (crc << 1) ^ ((crc & 0x80000000) ? CRCPOLY_BE :
173 0);
174 }
175 return crc;
176}
177
178#else /* Table-based approach */
179u32 __attribute_pure__ crc32_be(u32 crc, unsigned char const *p, size_t len)
180{
181# if CRC_BE_BITS == 8
182 const u32 *b =(u32 *)p;
183 const u32 *tab = crc32table_be;
184
185# ifdef __LITTLE_ENDIAN
186# define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8)
187# else
188# define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8)
189# endif
190
191 crc = __cpu_to_be32(crc);
192 /* Align it */
193 if(unlikely(((long)b)&3 && len)){
194 do {
195 u8 *p = (u8 *)b;
196 DO_CRC(*p++);
197 b = (u32 *)p;
198 } while ((--len) && ((long)b)&3 );
199 }
200 if(likely(len >= 4)){
201 /* load data 32 bits wide, xor data 32 bits wide. */
202 size_t save_len = len & 3;
Wolfgang Denk93e14592013-10-04 17:43:24 +0200203 len = len >> 2;
Kyungmin Parkf399d4a2008-11-19 16:23:06 +0100204 --b; /* use pre increment below(*++b) for speed */
205 do {
206 crc ^= *++b;
207 DO_CRC(0);
208 DO_CRC(0);
209 DO_CRC(0);
210 DO_CRC(0);
211 } while (--len);
212 b++; /* point to next byte(s) */
213 len = save_len;
214 }
215 /* And the last few bytes */
216 if(len){
217 do {
218 u8 *p = (u8 *)b;
219 DO_CRC(*p++);
220 b = (void *)p;
221 } while (--len);
222 }
223 return __be32_to_cpu(crc);
224#undef ENDIAN_SHIFT
225#undef DO_CRC
226
227# elif CRC_BE_BITS == 4
228 while (len--) {
229 crc ^= *p++ << 24;
230 crc = (crc << 4) ^ crc32table_be[crc >> 28];
231 crc = (crc << 4) ^ crc32table_be[crc >> 28];
232 }
233 return crc;
234# elif CRC_BE_BITS == 2
235 while (len--) {
236 crc ^= *p++ << 24;
237 crc = (crc << 2) ^ crc32table_be[crc >> 30];
238 crc = (crc << 2) ^ crc32table_be[crc >> 30];
239 crc = (crc << 2) ^ crc32table_be[crc >> 30];
240 crc = (crc << 2) ^ crc32table_be[crc >> 30];
241 }
242 return crc;
243# endif
244}
245#endif
246
247EXPORT_SYMBOL(crc32_le);
248EXPORT_SYMBOL(crc32_be);
249#endif
250/*
251 * A brief CRC tutorial.
252 *
253 * A CRC is a long-division remainder. You add the CRC to the message,
254 * and the whole thing (message+CRC) is a multiple of the given
255 * CRC polynomial. To check the CRC, you can either check that the
256 * CRC matches the recomputed value, *or* you can check that the
257 * remainder computed on the message+CRC is 0. This latter approach
258 * is used by a lot of hardware implementations, and is why so many
259 * protocols put the end-of-frame flag after the CRC.
260 *
261 * It's actually the same long division you learned in school, except that
262 * - We're working in binary, so the digits are only 0 and 1, and
263 * - When dividing polynomials, there are no carries. Rather than add and
264 * subtract, we just xor. Thus, we tend to get a bit sloppy about
265 * the difference between adding and subtracting.
266 *
267 * A 32-bit CRC polynomial is actually 33 bits long. But since it's
268 * 33 bits long, bit 32 is always going to be set, so usually the CRC
269 * is written in hex with the most significant bit omitted. (If you're
270 * familiar with the IEEE 754 floating-point format, it's the same idea.)
271 *
272 * Note that a CRC is computed over a string of *bits*, so you have
273 * to decide on the endianness of the bits within each byte. To get
274 * the best error-detecting properties, this should correspond to the
275 * order they're actually sent. For example, standard RS-232 serial is
276 * little-endian; the most significant bit (sometimes used for parity)
277 * is sent last. And when appending a CRC word to a message, you should
278 * do it in the right order, matching the endianness.
279 *
280 * Just like with ordinary division, the remainder is always smaller than
281 * the divisor (the CRC polynomial) you're dividing by. Each step of the
282 * division, you take one more digit (bit) of the dividend and append it
283 * to the current remainder. Then you figure out the appropriate multiple
284 * of the divisor to subtract to being the remainder back into range.
285 * In binary, it's easy - it has to be either 0 or 1, and to make the
286 * XOR cancel, it's just a copy of bit 32 of the remainder.
287 *
288 * When computing a CRC, we don't care about the quotient, so we can
289 * throw the quotient bit away, but subtract the appropriate multiple of
290 * the polynomial from the remainder and we're back to where we started,
291 * ready to process the next bit.
292 *
293 * A big-endian CRC written this way would be coded like:
294 * for (i = 0; i < input_bits; i++) {
295 * multiple = remainder & 0x80000000 ? CRCPOLY : 0;
296 * remainder = (remainder << 1 | next_input_bit()) ^ multiple;
297 * }
298 * Notice how, to get at bit 32 of the shifted remainder, we look
299 * at bit 31 of the remainder *before* shifting it.
300 *
301 * But also notice how the next_input_bit() bits we're shifting into
302 * the remainder don't actually affect any decision-making until
303 * 32 bits later. Thus, the first 32 cycles of this are pretty boring.
304 * Also, to add the CRC to a message, we need a 32-bit-long hole for it at
305 * the end, so we have to add 32 extra cycles shifting in zeros at the
306 * end of every message,
307 *
308 * So the standard trick is to rearrage merging in the next_input_bit()
309 * until the moment it's needed. Then the first 32 cycles can be precomputed,
310 * and merging in the final 32 zero bits to make room for the CRC can be
311 * skipped entirely.
312 * This changes the code to:
313 * for (i = 0; i < input_bits; i++) {
314 * remainder ^= next_input_bit() << 31;
315 * multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
316 * remainder = (remainder << 1) ^ multiple;
317 * }
318 * With this optimization, the little-endian code is simpler:
319 * for (i = 0; i < input_bits; i++) {
320 * remainder ^= next_input_bit();
321 * multiple = (remainder & 1) ? CRCPOLY : 0;
322 * remainder = (remainder >> 1) ^ multiple;
323 * }
324 *
325 * Note that the other details of endianness have been hidden in CRCPOLY
326 * (which must be bit-reversed) and next_input_bit().
327 *
328 * However, as long as next_input_bit is returning the bits in a sensible
329 * order, we can actually do the merging 8 or more bits at a time rather
330 * than one bit at a time:
331 * for (i = 0; i < input_bytes; i++) {
332 * remainder ^= next_input_byte() << 24;
333 * for (j = 0; j < 8; j++) {
334 * multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
335 * remainder = (remainder << 1) ^ multiple;
336 * }
337 * }
338 * Or in little-endian:
339 * for (i = 0; i < input_bytes; i++) {
340 * remainder ^= next_input_byte();
341 * for (j = 0; j < 8; j++) {
342 * multiple = (remainder & 1) ? CRCPOLY : 0;
343 * remainder = (remainder << 1) ^ multiple;
344 * }
345 * }
346 * If the input is a multiple of 32 bits, you can even XOR in a 32-bit
347 * word at a time and increase the inner loop count to 32.
348 *
349 * You can also mix and match the two loop styles, for example doing the
350 * bulk of a message byte-at-a-time and adding bit-at-a-time processing
351 * for any fractional bytes at the end.
352 *
353 * The only remaining optimization is to the byte-at-a-time table method.
354 * Here, rather than just shifting one bit of the remainder to decide
355 * in the correct multiple to subtract, we can shift a byte at a time.
356 * This produces a 40-bit (rather than a 33-bit) intermediate remainder,
357 * but again the multiple of the polynomial to subtract depends only on
358 * the high bits, the high 8 bits in this case.
359 *
360 * The multile we need in that case is the low 32 bits of a 40-bit
361 * value whose high 8 bits are given, and which is a multiple of the
362 * generator polynomial. This is simply the CRC-32 of the given
363 * one-byte message.
364 *
365 * Two more details: normally, appending zero bits to a message which
366 * is already a multiple of a polynomial produces a larger multiple of that
367 * polynomial. To enable a CRC to detect this condition, it's common to
368 * invert the CRC before appending it. This makes the remainder of the
369 * message+crc come out not as zero, but some fixed non-zero value.
370 *
371 * The same problem applies to zero bits prepended to the message, and
372 * a similar solution is used. Instead of starting with a remainder of
373 * 0, an initial remainder of all ones is used. As long as you start
374 * the same way on decoding, it doesn't make a difference.
375 */
376
377#ifdef UNITTEST
378
379#include <stdlib.h>
380#include <stdio.h>
381
382#ifdef UBI_LINUX /*Not used at present */
383static void
384buf_dump(char const *prefix, unsigned char const *buf, size_t len)
385{
386 fputs(prefix, stdout);
387 while (len--)
388 printf(" %02x", *buf++);
389 putchar('\n');
390
391}
392#endif
393
394static void bytereverse(unsigned char *buf, size_t len)
395{
396 while (len--) {
397 unsigned char x = bitrev8(*buf);
398 *buf++ = x;
399 }
400}
401
402static void random_garbage(unsigned char *buf, size_t len)
403{
404 while (len--)
405 *buf++ = (unsigned char) random();
406}
407
408#ifdef UBI_LINUX /* Not used at present */
409static void store_le(u32 x, unsigned char *buf)
410{
411 buf[0] = (unsigned char) x;
412 buf[1] = (unsigned char) (x >> 8);
413 buf[2] = (unsigned char) (x >> 16);
414 buf[3] = (unsigned char) (x >> 24);
415}
416#endif
417
418static void store_be(u32 x, unsigned char *buf)
419{
420 buf[0] = (unsigned char) (x >> 24);
421 buf[1] = (unsigned char) (x >> 16);
422 buf[2] = (unsigned char) (x >> 8);
423 buf[3] = (unsigned char) x;
424}
425
426/*
427 * This checks that CRC(buf + CRC(buf)) = 0, and that
428 * CRC commutes with bit-reversal. This has the side effect
429 * of bytewise bit-reversing the input buffer, and returns
430 * the CRC of the reversed buffer.
431 */
432static u32 test_step(u32 init, unsigned char *buf, size_t len)
433{
434 u32 crc1, crc2;
435 size_t i;
436
437 crc1 = crc32_be(init, buf, len);
438 store_be(crc1, buf + len);
439 crc2 = crc32_be(init, buf, len + 4);
440 if (crc2)
441 printf("\nCRC cancellation fail: 0x%08x should be 0\n",
442 crc2);
443
444 for (i = 0; i <= len + 4; i++) {
445 crc2 = crc32_be(init, buf, i);
446 crc2 = crc32_be(crc2, buf + i, len + 4 - i);
447 if (crc2)
448 printf("\nCRC split fail: 0x%08x\n", crc2);
449 }
450
451 /* Now swap it around for the other test */
452
453 bytereverse(buf, len + 4);
454 init = bitrev32(init);
455 crc2 = bitrev32(crc1);
456 if (crc1 != bitrev32(crc2))
457 printf("\nBit reversal fail: 0x%08x -> 0x%08x -> 0x%08x\n",
458 crc1, crc2, bitrev32(crc2));
459 crc1 = crc32_le(init, buf, len);
460 if (crc1 != crc2)
461 printf("\nCRC endianness fail: 0x%08x != 0x%08x\n", crc1,
462 crc2);
463 crc2 = crc32_le(init, buf, len + 4);
464 if (crc2)
465 printf("\nCRC cancellation fail: 0x%08x should be 0\n",
466 crc2);
467
468 for (i = 0; i <= len + 4; i++) {
469 crc2 = crc32_le(init, buf, i);
470 crc2 = crc32_le(crc2, buf + i, len + 4 - i);
471 if (crc2)
472 printf("\nCRC split fail: 0x%08x\n", crc2);
473 }
474
475 return crc1;
476}
477
478#define SIZE 64
479#define INIT1 0
480#define INIT2 0
481
482int main(void)
483{
484 unsigned char buf1[SIZE + 4];
485 unsigned char buf2[SIZE + 4];
486 unsigned char buf3[SIZE + 4];
487 int i, j;
488 u32 crc1, crc2, crc3;
489
490 for (i = 0; i <= SIZE; i++) {
491 printf("\rTesting length %d...", i);
492 fflush(stdout);
493 random_garbage(buf1, i);
494 random_garbage(buf2, i);
495 for (j = 0; j < i; j++)
496 buf3[j] = buf1[j] ^ buf2[j];
497
498 crc1 = test_step(INIT1, buf1, i);
499 crc2 = test_step(INIT2, buf2, i);
500 /* Now check that CRC(buf1 ^ buf2) = CRC(buf1) ^ CRC(buf2) */
501 crc3 = test_step(INIT1 ^ INIT2, buf3, i);
502 if (crc3 != (crc1 ^ crc2))
503 printf("CRC XOR fail: 0x%08x != 0x%08x ^ 0x%08x\n",
504 crc3, crc1, crc2);
505 }
506 printf("\nAll test complete. No failures expected.\n");
507 return 0;
508}
509
510#endif /* UNITTEST */