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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
41# define __force
42#ifndef __constant_cpu_to_le32
43#define __constant_cpu_to_le32(x) ((__force __le32)(__u32)(x))
44#endif
45#ifndef __constant_le32_to_cpu
46#define __constant_le32_to_cpu(x) ((__force __u32)(__le32)(x))
47#endif
48
49#if CRC_LE_BITS == 8
50#define tole(x) __constant_cpu_to_le32(x)
51#define tobe(x) __constant_cpu_to_be32(x)
52#else
53#define tole(x) (x)
54#define tobe(x) (x)
55#endif
56#include "crc32table.h"
57#ifdef UBI_LINUX
58MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
59MODULE_DESCRIPTION("Ethernet CRC32 calculations");
60MODULE_LICENSE("GPL");
61#endif
62/**
63 * crc32_le() - Calculate bitwise little-endian Ethernet AUTODIN II CRC32
64 * @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for
65 * other uses, or the previous crc32 value if computing incrementally.
66 * @p: pointer to buffer over which CRC is run
67 * @len: length of buffer @p
68 */
69u32 crc32_le(u32 crc, unsigned char const *p, size_t len);
70
71#if CRC_LE_BITS == 1
72/*
73 * In fact, the table-based code will work in this case, but it can be
74 * simplified by inlining the table in ?: form.
75 */
76
77u32 crc32_le(u32 crc, unsigned char const *p, size_t len)
78{
79 int i;
80 while (len--) {
81 crc ^= *p++;
82 for (i = 0; i < 8; i++)
83 crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0);
84 }
85 return crc;
86}
87#else /* Table-based approach */
88
89u32 crc32_le(u32 crc, unsigned char const *p, size_t len)
90{
91# if CRC_LE_BITS == 8
92 const u32 *b =(u32 *)p;
93 const u32 *tab = crc32table_le;
94
95# ifdef __LITTLE_ENDIAN
96# define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8)
97# else
98# define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8)
99# endif
100 //printf("Crc32_le crc=%x\n",crc);
101 crc = __cpu_to_le32(crc);
102 /* Align it */
103 if((((long)b)&3 && len)){
104 do {
105 u8 *p = (u8 *)b;
106 DO_CRC(*p++);
107 b = (void *)p;
108 } while ((--len) && ((long)b)&3 );
109 }
110 if((len >= 4)){
111 /* load data 32 bits wide, xor data 32 bits wide. */
112 size_t save_len = len & 3;
113 len = len >> 2;
114 --b; /* use pre increment below(*++b) for speed */
115 do {
116 crc ^= *++b;
117 DO_CRC(0);
118 DO_CRC(0);
119 DO_CRC(0);
120 DO_CRC(0);
121 } while (--len);
122 b++; /* point to next byte(s) */
123 len = save_len;
124 }
125 /* And the last few bytes */
126 if(len){
127 do {
128 u8 *p = (u8 *)b;
129 DO_CRC(*p++);
130 b = (void *)p;
131 } while (--len);
132 }
133
134 return __le32_to_cpu(crc);
135#undef ENDIAN_SHIFT
136#undef DO_CRC
137
138# elif CRC_LE_BITS == 4
139 while (len--) {
140 crc ^= *p++;
141 crc = (crc >> 4) ^ crc32table_le[crc & 15];
142 crc = (crc >> 4) ^ crc32table_le[crc & 15];
143 }
144 return crc;
145# elif CRC_LE_BITS == 2
146 while (len--) {
147 crc ^= *p++;
148 crc = (crc >> 2) ^ crc32table_le[crc & 3];
149 crc = (crc >> 2) ^ crc32table_le[crc & 3];
150 crc = (crc >> 2) ^ crc32table_le[crc & 3];
151 crc = (crc >> 2) ^ crc32table_le[crc & 3];
152 }
153 return crc;
154# endif
155}
156#endif
157#ifdef UBI_LINUX
158/**
159 * crc32_be() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
160 * @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for
161 * other uses, or the previous crc32 value if computing incrementally.
162 * @p: pointer to buffer over which CRC is run
163 * @len: length of buffer @p
164 */
165u32 __attribute_pure__ crc32_be(u32 crc, unsigned char const *p, size_t len);
166
167#if CRC_BE_BITS == 1
168/*
169 * In fact, the table-based code will work in this case, but it can be
170 * simplified by inlining the table in ?: form.
171 */
172
173u32 __attribute_pure__ crc32_be(u32 crc, unsigned char const *p, size_t len)
174{
175 int i;
176 while (len--) {
177 crc ^= *p++ << 24;
178 for (i = 0; i < 8; i++)
179 crc =
180 (crc << 1) ^ ((crc & 0x80000000) ? CRCPOLY_BE :
181 0);
182 }
183 return crc;
184}
185
186#else /* Table-based approach */
187u32 __attribute_pure__ crc32_be(u32 crc, unsigned char const *p, size_t len)
188{
189# if CRC_BE_BITS == 8
190 const u32 *b =(u32 *)p;
191 const u32 *tab = crc32table_be;
192
193# ifdef __LITTLE_ENDIAN
194# define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8)
195# else
196# define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8)
197# endif
198
199 crc = __cpu_to_be32(crc);
200 /* Align it */
201 if(unlikely(((long)b)&3 && len)){
202 do {
203 u8 *p = (u8 *)b;
204 DO_CRC(*p++);
205 b = (u32 *)p;
206 } while ((--len) && ((long)b)&3 );
207 }
208 if(likely(len >= 4)){
209 /* load data 32 bits wide, xor data 32 bits wide. */
210 size_t save_len = len & 3;
211 len = len >> 2;
212 --b; /* use pre increment below(*++b) for speed */
213 do {
214 crc ^= *++b;
215 DO_CRC(0);
216 DO_CRC(0);
217 DO_CRC(0);
218 DO_CRC(0);
219 } while (--len);
220 b++; /* point to next byte(s) */
221 len = save_len;
222 }
223 /* And the last few bytes */
224 if(len){
225 do {
226 u8 *p = (u8 *)b;
227 DO_CRC(*p++);
228 b = (void *)p;
229 } while (--len);
230 }
231 return __be32_to_cpu(crc);
232#undef ENDIAN_SHIFT
233#undef DO_CRC
234
235# elif CRC_BE_BITS == 4
236 while (len--) {
237 crc ^= *p++ << 24;
238 crc = (crc << 4) ^ crc32table_be[crc >> 28];
239 crc = (crc << 4) ^ crc32table_be[crc >> 28];
240 }
241 return crc;
242# elif CRC_BE_BITS == 2
243 while (len--) {
244 crc ^= *p++ << 24;
245 crc = (crc << 2) ^ crc32table_be[crc >> 30];
246 crc = (crc << 2) ^ crc32table_be[crc >> 30];
247 crc = (crc << 2) ^ crc32table_be[crc >> 30];
248 crc = (crc << 2) ^ crc32table_be[crc >> 30];
249 }
250 return crc;
251# endif
252}
253#endif
254
255EXPORT_SYMBOL(crc32_le);
256EXPORT_SYMBOL(crc32_be);
257#endif
258/*
259 * A brief CRC tutorial.
260 *
261 * A CRC is a long-division remainder. You add the CRC to the message,
262 * and the whole thing (message+CRC) is a multiple of the given
263 * CRC polynomial. To check the CRC, you can either check that the
264 * CRC matches the recomputed value, *or* you can check that the
265 * remainder computed on the message+CRC is 0. This latter approach
266 * is used by a lot of hardware implementations, and is why so many
267 * protocols put the end-of-frame flag after the CRC.
268 *
269 * It's actually the same long division you learned in school, except that
270 * - We're working in binary, so the digits are only 0 and 1, and
271 * - When dividing polynomials, there are no carries. Rather than add and
272 * subtract, we just xor. Thus, we tend to get a bit sloppy about
273 * the difference between adding and subtracting.
274 *
275 * A 32-bit CRC polynomial is actually 33 bits long. But since it's
276 * 33 bits long, bit 32 is always going to be set, so usually the CRC
277 * is written in hex with the most significant bit omitted. (If you're
278 * familiar with the IEEE 754 floating-point format, it's the same idea.)
279 *
280 * Note that a CRC is computed over a string of *bits*, so you have
281 * to decide on the endianness of the bits within each byte. To get
282 * the best error-detecting properties, this should correspond to the
283 * order they're actually sent. For example, standard RS-232 serial is
284 * little-endian; the most significant bit (sometimes used for parity)
285 * is sent last. And when appending a CRC word to a message, you should
286 * do it in the right order, matching the endianness.
287 *
288 * Just like with ordinary division, the remainder is always smaller than
289 * the divisor (the CRC polynomial) you're dividing by. Each step of the
290 * division, you take one more digit (bit) of the dividend and append it
291 * to the current remainder. Then you figure out the appropriate multiple
292 * of the divisor to subtract to being the remainder back into range.
293 * In binary, it's easy - it has to be either 0 or 1, and to make the
294 * XOR cancel, it's just a copy of bit 32 of the remainder.
295 *
296 * When computing a CRC, we don't care about the quotient, so we can
297 * throw the quotient bit away, but subtract the appropriate multiple of
298 * the polynomial from the remainder and we're back to where we started,
299 * ready to process the next bit.
300 *
301 * A big-endian CRC written this way would be coded like:
302 * for (i = 0; i < input_bits; i++) {
303 * multiple = remainder & 0x80000000 ? CRCPOLY : 0;
304 * remainder = (remainder << 1 | next_input_bit()) ^ multiple;
305 * }
306 * Notice how, to get at bit 32 of the shifted remainder, we look
307 * at bit 31 of the remainder *before* shifting it.
308 *
309 * But also notice how the next_input_bit() bits we're shifting into
310 * the remainder don't actually affect any decision-making until
311 * 32 bits later. Thus, the first 32 cycles of this are pretty boring.
312 * Also, to add the CRC to a message, we need a 32-bit-long hole for it at
313 * the end, so we have to add 32 extra cycles shifting in zeros at the
314 * end of every message,
315 *
316 * So the standard trick is to rearrage merging in the next_input_bit()
317 * until the moment it's needed. Then the first 32 cycles can be precomputed,
318 * and merging in the final 32 zero bits to make room for the CRC can be
319 * skipped entirely.
320 * This changes the code to:
321 * for (i = 0; i < input_bits; i++) {
322 * remainder ^= next_input_bit() << 31;
323 * multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
324 * remainder = (remainder << 1) ^ multiple;
325 * }
326 * With this optimization, the little-endian code is simpler:
327 * for (i = 0; i < input_bits; i++) {
328 * remainder ^= next_input_bit();
329 * multiple = (remainder & 1) ? CRCPOLY : 0;
330 * remainder = (remainder >> 1) ^ multiple;
331 * }
332 *
333 * Note that the other details of endianness have been hidden in CRCPOLY
334 * (which must be bit-reversed) and next_input_bit().
335 *
336 * However, as long as next_input_bit is returning the bits in a sensible
337 * order, we can actually do the merging 8 or more bits at a time rather
338 * than one bit at a time:
339 * for (i = 0; i < input_bytes; i++) {
340 * remainder ^= next_input_byte() << 24;
341 * for (j = 0; j < 8; j++) {
342 * multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
343 * remainder = (remainder << 1) ^ multiple;
344 * }
345 * }
346 * Or in little-endian:
347 * for (i = 0; i < input_bytes; i++) {
348 * remainder ^= next_input_byte();
349 * for (j = 0; j < 8; j++) {
350 * multiple = (remainder & 1) ? CRCPOLY : 0;
351 * remainder = (remainder << 1) ^ multiple;
352 * }
353 * }
354 * If the input is a multiple of 32 bits, you can even XOR in a 32-bit
355 * word at a time and increase the inner loop count to 32.
356 *
357 * You can also mix and match the two loop styles, for example doing the
358 * bulk of a message byte-at-a-time and adding bit-at-a-time processing
359 * for any fractional bytes at the end.
360 *
361 * The only remaining optimization is to the byte-at-a-time table method.
362 * Here, rather than just shifting one bit of the remainder to decide
363 * in the correct multiple to subtract, we can shift a byte at a time.
364 * This produces a 40-bit (rather than a 33-bit) intermediate remainder,
365 * but again the multiple of the polynomial to subtract depends only on
366 * the high bits, the high 8 bits in this case.
367 *
368 * The multile we need in that case is the low 32 bits of a 40-bit
369 * value whose high 8 bits are given, and which is a multiple of the
370 * generator polynomial. This is simply the CRC-32 of the given
371 * one-byte message.
372 *
373 * Two more details: normally, appending zero bits to a message which
374 * is already a multiple of a polynomial produces a larger multiple of that
375 * polynomial. To enable a CRC to detect this condition, it's common to
376 * invert the CRC before appending it. This makes the remainder of the
377 * message+crc come out not as zero, but some fixed non-zero value.
378 *
379 * The same problem applies to zero bits prepended to the message, and
380 * a similar solution is used. Instead of starting with a remainder of
381 * 0, an initial remainder of all ones is used. As long as you start
382 * the same way on decoding, it doesn't make a difference.
383 */
384
385#ifdef UNITTEST
386
387#include <stdlib.h>
388#include <stdio.h>
389
390#ifdef UBI_LINUX /*Not used at present */
391static void
392buf_dump(char const *prefix, unsigned char const *buf, size_t len)
393{
394 fputs(prefix, stdout);
395 while (len--)
396 printf(" %02x", *buf++);
397 putchar('\n');
398
399}
400#endif
401
402static void bytereverse(unsigned char *buf, size_t len)
403{
404 while (len--) {
405 unsigned char x = bitrev8(*buf);
406 *buf++ = x;
407 }
408}
409
410static void random_garbage(unsigned char *buf, size_t len)
411{
412 while (len--)
413 *buf++ = (unsigned char) random();
414}
415
416#ifdef UBI_LINUX /* Not used at present */
417static void store_le(u32 x, unsigned char *buf)
418{
419 buf[0] = (unsigned char) x;
420 buf[1] = (unsigned char) (x >> 8);
421 buf[2] = (unsigned char) (x >> 16);
422 buf[3] = (unsigned char) (x >> 24);
423}
424#endif
425
426static void store_be(u32 x, unsigned char *buf)
427{
428 buf[0] = (unsigned char) (x >> 24);
429 buf[1] = (unsigned char) (x >> 16);
430 buf[2] = (unsigned char) (x >> 8);
431 buf[3] = (unsigned char) x;
432}
433
434/*
435 * This checks that CRC(buf + CRC(buf)) = 0, and that
436 * CRC commutes with bit-reversal. This has the side effect
437 * of bytewise bit-reversing the input buffer, and returns
438 * the CRC of the reversed buffer.
439 */
440static u32 test_step(u32 init, unsigned char *buf, size_t len)
441{
442 u32 crc1, crc2;
443 size_t i;
444
445 crc1 = crc32_be(init, buf, len);
446 store_be(crc1, buf + len);
447 crc2 = crc32_be(init, buf, len + 4);
448 if (crc2)
449 printf("\nCRC cancellation fail: 0x%08x should be 0\n",
450 crc2);
451
452 for (i = 0; i <= len + 4; i++) {
453 crc2 = crc32_be(init, buf, i);
454 crc2 = crc32_be(crc2, buf + i, len + 4 - i);
455 if (crc2)
456 printf("\nCRC split fail: 0x%08x\n", crc2);
457 }
458
459 /* Now swap it around for the other test */
460
461 bytereverse(buf, len + 4);
462 init = bitrev32(init);
463 crc2 = bitrev32(crc1);
464 if (crc1 != bitrev32(crc2))
465 printf("\nBit reversal fail: 0x%08x -> 0x%08x -> 0x%08x\n",
466 crc1, crc2, bitrev32(crc2));
467 crc1 = crc32_le(init, buf, len);
468 if (crc1 != crc2)
469 printf("\nCRC endianness fail: 0x%08x != 0x%08x\n", crc1,
470 crc2);
471 crc2 = crc32_le(init, buf, len + 4);
472 if (crc2)
473 printf("\nCRC cancellation fail: 0x%08x should be 0\n",
474 crc2);
475
476 for (i = 0; i <= len + 4; i++) {
477 crc2 = crc32_le(init, buf, i);
478 crc2 = crc32_le(crc2, buf + i, len + 4 - i);
479 if (crc2)
480 printf("\nCRC split fail: 0x%08x\n", crc2);
481 }
482
483 return crc1;
484}
485
486#define SIZE 64
487#define INIT1 0
488#define INIT2 0
489
490int main(void)
491{
492 unsigned char buf1[SIZE + 4];
493 unsigned char buf2[SIZE + 4];
494 unsigned char buf3[SIZE + 4];
495 int i, j;
496 u32 crc1, crc2, crc3;
497
498 for (i = 0; i <= SIZE; i++) {
499 printf("\rTesting length %d...", i);
500 fflush(stdout);
501 random_garbage(buf1, i);
502 random_garbage(buf2, i);
503 for (j = 0; j < i; j++)
504 buf3[j] = buf1[j] ^ buf2[j];
505
506 crc1 = test_step(INIT1, buf1, i);
507 crc2 = test_step(INIT2, buf2, i);
508 /* Now check that CRC(buf1 ^ buf2) = CRC(buf1) ^ CRC(buf2) */
509 crc3 = test_step(INIT1 ^ INIT2, buf3, i);
510 if (crc3 != (crc1 ^ crc2))
511 printf("CRC XOR fail: 0x%08x != 0x%08x ^ 0x%08x\n",
512 crc3, crc1, crc2);
513 }
514 printf("\nAll test complete. No failures expected.\n");
515 return 0;
516}
517
518#endif /* UNITTEST */