Root/lib/crc32.c

Source at commit b386be689295730688885552666ea40b2e639b14 created 8 years 11 months ago.
By Maarten ter Huurne, Revert "MIPS: JZ4740: reset: Initialize hibernate wakeup counters."
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/init.h>
29#include <linux/atomic.h>
30#include "crc32defs.h"
31#if CRC_LE_BITS == 8
32# define tole(x) __constant_cpu_to_le32(x)
33#else
34# define tole(x) (x)
35#endif
36
37#if CRC_BE_BITS == 8
38# define tobe(x) __constant_cpu_to_be32(x)
39#else
40# define tobe(x) (x)
41#endif
42#include "crc32table.h"
43
44MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
45MODULE_DESCRIPTION("Ethernet CRC32 calculations");
46MODULE_LICENSE("GPL");
47
48#if CRC_LE_BITS == 8 || CRC_BE_BITS == 8
49
50static inline u32
51crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256])
52{
53# ifdef __LITTLE_ENDIAN
54# define DO_CRC(x) crc = t0[(crc ^ (x)) & 255] ^ (crc >> 8)
55# define DO_CRC4 crc = t3[(crc) & 255] ^ \
56        t2[(crc >> 8) & 255] ^ \
57        t1[(crc >> 16) & 255] ^ \
58        t0[(crc >> 24) & 255]
59# else
60# define DO_CRC(x) crc = t0[((crc >> 24) ^ (x)) & 255] ^ (crc << 8)
61# define DO_CRC4 crc = t0[(crc) & 255] ^ \
62        t1[(crc >> 8) & 255] ^ \
63        t2[(crc >> 16) & 255] ^ \
64        t3[(crc >> 24) & 255]
65# endif
66    const u32 *b;
67    size_t rem_len;
68    const u32 *t0=tab[0], *t1=tab[1], *t2=tab[2], *t3=tab[3];
69
70    /* Align it */
71    if (unlikely((long)buf & 3 && len)) {
72        do {
73            DO_CRC(*buf++);
74        } while ((--len) && ((long)buf)&3);
75    }
76    rem_len = len & 3;
77    /* load data 32 bits wide, xor data 32 bits wide. */
78    len = len >> 2;
79    b = (const u32 *)buf;
80    for (--b; len; --len) {
81        crc ^= *++b; /* use pre increment for speed */
82        DO_CRC4;
83    }
84    len = rem_len;
85    /* And the last few bytes */
86    if (len) {
87        u8 *p = (u8 *)(b + 1) - 1;
88        do {
89            DO_CRC(*++p); /* use pre increment for speed */
90        } while (--len);
91    }
92    return crc;
93#undef DO_CRC
94#undef DO_CRC4
95}
96#endif
97/**
98 * crc32_le() - Calculate bitwise little-endian Ethernet AUTODIN II CRC32
99 * @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for
100 * other uses, or the previous crc32 value if computing incrementally.
101 * @p: pointer to buffer over which CRC is run
102 * @len: length of buffer @p
103 */
104u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len);
105
106#if CRC_LE_BITS == 1
107/*
108 * In fact, the table-based code will work in this case, but it can be
109 * simplified by inlining the table in ?: form.
110 */
111
112u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
113{
114    int i;
115    while (len--) {
116        crc ^= *p++;
117        for (i = 0; i < 8; i++)
118            crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0);
119    }
120    return crc;
121}
122#else /* Table-based approach */
123
124u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
125{
126# if CRC_LE_BITS == 8
127    const u32 (*tab)[] = crc32table_le;
128
129    crc = __cpu_to_le32(crc);
130    crc = crc32_body(crc, p, len, tab);
131    return __le32_to_cpu(crc);
132# elif CRC_LE_BITS == 4
133    while (len--) {
134        crc ^= *p++;
135        crc = (crc >> 4) ^ crc32table_le[crc & 15];
136        crc = (crc >> 4) ^ crc32table_le[crc & 15];
137    }
138    return crc;
139# elif CRC_LE_BITS == 2
140    while (len--) {
141        crc ^= *p++;
142        crc = (crc >> 2) ^ crc32table_le[crc & 3];
143        crc = (crc >> 2) ^ crc32table_le[crc & 3];
144        crc = (crc >> 2) ^ crc32table_le[crc & 3];
145        crc = (crc >> 2) ^ crc32table_le[crc & 3];
146    }
147    return crc;
148# endif
149}
150#endif
151
152/**
153 * crc32_be() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
154 * @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for
155 * other uses, or the previous crc32 value if computing incrementally.
156 * @p: pointer to buffer over which CRC is run
157 * @len: length of buffer @p
158 */
159u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len);
160
161#if CRC_BE_BITS == 1
162/*
163 * In fact, the table-based code will work in this case, but it can be
164 * simplified by inlining the table in ?: form.
165 */
166
167u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
168{
169    int i;
170    while (len--) {
171        crc ^= *p++ << 24;
172        for (i = 0; i < 8; i++)
173            crc =
174                (crc << 1) ^ ((crc & 0x80000000) ? CRCPOLY_BE :
175                      0);
176    }
177    return crc;
178}
179
180#else /* Table-based approach */
181u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
182{
183# if CRC_BE_BITS == 8
184    const u32 (*tab)[] = crc32table_be;
185
186    crc = __cpu_to_be32(crc);
187    crc = crc32_body(crc, p, len, tab);
188    return __be32_to_cpu(crc);
189# elif CRC_BE_BITS == 4
190    while (len--) {
191        crc ^= *p++ << 24;
192        crc = (crc << 4) ^ crc32table_be[crc >> 28];
193        crc = (crc << 4) ^ crc32table_be[crc >> 28];
194    }
195    return crc;
196# elif CRC_BE_BITS == 2
197    while (len--) {
198        crc ^= *p++ << 24;
199        crc = (crc << 2) ^ crc32table_be[crc >> 30];
200        crc = (crc << 2) ^ crc32table_be[crc >> 30];
201        crc = (crc << 2) ^ crc32table_be[crc >> 30];
202        crc = (crc << 2) ^ crc32table_be[crc >> 30];
203    }
204    return crc;
205# endif
206}
207#endif
208
209EXPORT_SYMBOL(crc32_le);
210EXPORT_SYMBOL(crc32_be);
211
212/*
213 * A brief CRC tutorial.
214 *
215 * A CRC is a long-division remainder. You add the CRC to the message,
216 * and the whole thing (message+CRC) is a multiple of the given
217 * CRC polynomial. To check the CRC, you can either check that the
218 * CRC matches the recomputed value, *or* you can check that the
219 * remainder computed on the message+CRC is 0. This latter approach
220 * is used by a lot of hardware implementations, and is why so many
221 * protocols put the end-of-frame flag after the CRC.
222 *
223 * It's actually the same long division you learned in school, except that
224 * - We're working in binary, so the digits are only 0 and 1, and
225 * - When dividing polynomials, there are no carries. Rather than add and
226 * subtract, we just xor. Thus, we tend to get a bit sloppy about
227 * the difference between adding and subtracting.
228 *
229 * A 32-bit CRC polynomial is actually 33 bits long. But since it's
230 * 33 bits long, bit 32 is always going to be set, so usually the CRC
231 * is written in hex with the most significant bit omitted. (If you're
232 * familiar with the IEEE 754 floating-point format, it's the same idea.)
233 *
234 * Note that a CRC is computed over a string of *bits*, so you have
235 * to decide on the endianness of the bits within each byte. To get
236 * the best error-detecting properties, this should correspond to the
237 * order they're actually sent. For example, standard RS-232 serial is
238 * little-endian; the most significant bit (sometimes used for parity)
239 * is sent last. And when appending a CRC word to a message, you should
240 * do it in the right order, matching the endianness.
241 *
242 * Just like with ordinary division, the remainder is always smaller than
243 * the divisor (the CRC polynomial) you're dividing by. Each step of the
244 * division, you take one more digit (bit) of the dividend and append it
245 * to the current remainder. Then you figure out the appropriate multiple
246 * of the divisor to subtract to being the remainder back into range.
247 * In binary, it's easy - it has to be either 0 or 1, and to make the
248 * XOR cancel, it's just a copy of bit 32 of the remainder.
249 *
250 * When computing a CRC, we don't care about the quotient, so we can
251 * throw the quotient bit away, but subtract the appropriate multiple of
252 * the polynomial from the remainder and we're back to where we started,
253 * ready to process the next bit.
254 *
255 * A big-endian CRC written this way would be coded like:
256 * for (i = 0; i < input_bits; i++) {
257 * multiple = remainder & 0x80000000 ? CRCPOLY : 0;
258 * remainder = (remainder << 1 | next_input_bit()) ^ multiple;
259 * }
260 * Notice how, to get at bit 32 of the shifted remainder, we look
261 * at bit 31 of the remainder *before* shifting it.
262 *
263 * But also notice how the next_input_bit() bits we're shifting into
264 * the remainder don't actually affect any decision-making until
265 * 32 bits later. Thus, the first 32 cycles of this are pretty boring.
266 * Also, to add the CRC to a message, we need a 32-bit-long hole for it at
267 * the end, so we have to add 32 extra cycles shifting in zeros at the
268 * end of every message,
269 *
270 * So the standard trick is to rearrage merging in the next_input_bit()
271 * until the moment it's needed. Then the first 32 cycles can be precomputed,
272 * and merging in the final 32 zero bits to make room for the CRC can be
273 * skipped entirely.
274 * This changes the code to:
275 * for (i = 0; i < input_bits; i++) {
276 * remainder ^= next_input_bit() << 31;
277 * multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
278 * remainder = (remainder << 1) ^ multiple;
279 * }
280 * With this optimization, the little-endian code is simpler:
281 * for (i = 0; i < input_bits; i++) {
282 * remainder ^= next_input_bit();
283 * multiple = (remainder & 1) ? CRCPOLY : 0;
284 * remainder = (remainder >> 1) ^ multiple;
285 * }
286 *
287 * Note that the other details of endianness have been hidden in CRCPOLY
288 * (which must be bit-reversed) and next_input_bit().
289 *
290 * However, as long as next_input_bit is returning the bits in a sensible
291 * order, we can actually do the merging 8 or more bits at a time rather
292 * than one bit at a time:
293 * for (i = 0; i < input_bytes; i++) {
294 * remainder ^= next_input_byte() << 24;
295 * for (j = 0; j < 8; j++) {
296 * multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
297 * remainder = (remainder << 1) ^ multiple;
298 * }
299 * }
300 * Or in little-endian:
301 * for (i = 0; i < input_bytes; i++) {
302 * remainder ^= next_input_byte();
303 * for (j = 0; j < 8; j++) {
304 * multiple = (remainder & 1) ? CRCPOLY : 0;
305 * remainder = (remainder << 1) ^ multiple;
306 * }
307 * }
308 * If the input is a multiple of 32 bits, you can even XOR in a 32-bit
309 * word at a time and increase the inner loop count to 32.
310 *
311 * You can also mix and match the two loop styles, for example doing the
312 * bulk of a message byte-at-a-time and adding bit-at-a-time processing
313 * for any fractional bytes at the end.
314 *
315 * The only remaining optimization is to the byte-at-a-time table method.
316 * Here, rather than just shifting one bit of the remainder to decide
317 * in the correct multiple to subtract, we can shift a byte at a time.
318 * This produces a 40-bit (rather than a 33-bit) intermediate remainder,
319 * but again the multiple of the polynomial to subtract depends only on
320 * the high bits, the high 8 bits in this case.
321 *
322 * The multiple we need in that case is the low 32 bits of a 40-bit
323 * value whose high 8 bits are given, and which is a multiple of the
324 * generator polynomial. This is simply the CRC-32 of the given
325 * one-byte message.
326 *
327 * Two more details: normally, appending zero bits to a message which
328 * is already a multiple of a polynomial produces a larger multiple of that
329 * polynomial. To enable a CRC to detect this condition, it's common to
330 * invert the CRC before appending it. This makes the remainder of the
331 * message+crc come out not as zero, but some fixed non-zero value.
332 *
333 * The same problem applies to zero bits prepended to the message, and
334 * a similar solution is used. Instead of starting with a remainder of
335 * 0, an initial remainder of all ones is used. As long as you start
336 * the same way on decoding, it doesn't make a difference.
337 */
338
339#ifdef UNITTEST
340
341#include <stdlib.h>
342#include <stdio.h>
343
344#if 0 /*Not used at present */
345static void
346buf_dump(char const *prefix, unsigned char const *buf, size_t len)
347{
348    fputs(prefix, stdout);
349    while (len--)
350        printf(" %02x", *buf++);
351    putchar('\n');
352
353}
354#endif
355
356static void bytereverse(unsigned char *buf, size_t len)
357{
358    while (len--) {
359        unsigned char x = bitrev8(*buf);
360        *buf++ = x;
361    }
362}
363
364static void random_garbage(unsigned char *buf, size_t len)
365{
366    while (len--)
367        *buf++ = (unsigned char) random();
368}
369
370#if 0 /* Not used at present */
371static void store_le(u32 x, unsigned char *buf)
372{
373    buf[0] = (unsigned char) x;
374    buf[1] = (unsigned char) (x >> 8);
375    buf[2] = (unsigned char) (x >> 16);
376    buf[3] = (unsigned char) (x >> 24);
377}
378#endif
379
380static void store_be(u32 x, unsigned char *buf)
381{
382    buf[0] = (unsigned char) (x >> 24);
383    buf[1] = (unsigned char) (x >> 16);
384    buf[2] = (unsigned char) (x >> 8);
385    buf[3] = (unsigned char) x;
386}
387
388/*
389 * This checks that CRC(buf + CRC(buf)) = 0, and that
390 * CRC commutes with bit-reversal. This has the side effect
391 * of bytewise bit-reversing the input buffer, and returns
392 * the CRC of the reversed buffer.
393 */
394static u32 test_step(u32 init, unsigned char *buf, size_t len)
395{
396    u32 crc1, crc2;
397    size_t i;
398
399    crc1 = crc32_be(init, buf, len);
400    store_be(crc1, buf + len);
401    crc2 = crc32_be(init, buf, len + 4);
402    if (crc2)
403        printf("\nCRC cancellation fail: 0x%08x should be 0\n",
404               crc2);
405
406    for (i = 0; i <= len + 4; i++) {
407        crc2 = crc32_be(init, buf, i);
408        crc2 = crc32_be(crc2, buf + i, len + 4 - i);
409        if (crc2)
410            printf("\nCRC split fail: 0x%08x\n", crc2);
411    }
412
413    /* Now swap it around for the other test */
414
415    bytereverse(buf, len + 4);
416    init = bitrev32(init);
417    crc2 = bitrev32(crc1);
418    if (crc1 != bitrev32(crc2))
419        printf("\nBit reversal fail: 0x%08x -> 0x%08x -> 0x%08x\n",
420               crc1, crc2, bitrev32(crc2));
421    crc1 = crc32_le(init, buf, len);
422    if (crc1 != crc2)
423        printf("\nCRC endianness fail: 0x%08x != 0x%08x\n", crc1,
424               crc2);
425    crc2 = crc32_le(init, buf, len + 4);
426    if (crc2)
427        printf("\nCRC cancellation fail: 0x%08x should be 0\n",
428               crc2);
429
430    for (i = 0; i <= len + 4; i++) {
431        crc2 = crc32_le(init, buf, i);
432        crc2 = crc32_le(crc2, buf + i, len + 4 - i);
433        if (crc2)
434            printf("\nCRC split fail: 0x%08x\n", crc2);
435    }
436
437    return crc1;
438}
439
440#define SIZE 64
441#define INIT1 0
442#define INIT2 0
443
444int main(void)
445{
446    unsigned char buf1[SIZE + 4];
447    unsigned char buf2[SIZE + 4];
448    unsigned char buf3[SIZE + 4];
449    int i, j;
450    u32 crc1, crc2, crc3;
451
452    for (i = 0; i <= SIZE; i++) {
453        printf("\rTesting length %d...", i);
454        fflush(stdout);
455        random_garbage(buf1, i);
456        random_garbage(buf2, i);
457        for (j = 0; j < i; j++)
458            buf3[j] = buf1[j] ^ buf2[j];
459
460        crc1 = test_step(INIT1, buf1, i);
461        crc2 = test_step(INIT2, buf2, i);
462        /* Now check that CRC(buf1 ^ buf2) = CRC(buf1) ^ CRC(buf2) */
463        crc3 = test_step(INIT1 ^ INIT2, buf3, i);
464        if (crc3 != (crc1 ^ crc2))
465            printf("CRC XOR fail: 0x%08x != 0x%08x ^ 0x%08x\n",
466                   crc3, crc1, crc2);
467    }
468    printf("\nAll test complete. No failures expected.\n");
469    return 0;
470}
471
472#endif /* UNITTEST */
473

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