lib/crc32.c

   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 #if CRC_LE_BITS == 1
  46 /*
  47  * In fact, the table-based code will work in this case, but it can be
  48  * simplified by inlining the table in ?: form.
  49  */
  50
  51 /**
  52  * crc32_le() - Calculate bitwise little-endian Ethernet AUTODIN II CRC32
  53  * @crc - seed value for computation.  ~0 for Ethernet, sometimes 0 for
  54  *        other uses, or the previous crc32 value if computing incrementally.
  55  * @p   - pointer to buffer over which CRC is run
  56  * @len - length of buffer @p
  57  *
  58  */
  59 u32 __attribute_pure__ crc32_le(u32 crc, unsigned char const *p, size_t len)
  60 {
  61         int i;
  62         while (len--) {
  63                 crc ^= *p++;
  64                 for (i = 0; i < 8; i++)
  65                         crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0);
  66         }
  67         return crc;
  68 }
  69 #else                           /* Table-based approach */
  70
  71 /**
  72  * crc32_le() - Calculate bitwise little-endian Ethernet AUTODIN II CRC32
  73  * @crc - seed value for computation.  ~0 for Ethernet, sometimes 0 for
  74  *        other uses, or the previous crc32 value if computing incrementally.
  75  * @p   - pointer to buffer over which CRC is run
  76  * @len - length of buffer @p
  77  *
  78  */
  79 u32 __attribute_pure__ crc32_le(u32 crc, unsigned char const *p, size_t len)
  80 {
  81 # if CRC_LE_BITS == 8
  82         const u32      *b =(u32 *)p;
  83         const u32      *tab = crc32table_le;
  84
  85 # ifdef __LITTLE_ENDIAN
  86 #  define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8)
  87 # else
  88 #  define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8)
  89 # endif
  90
  91         crc = __cpu_to_le32(crc);
  92         /* Align it */
  93         if(unlikely(((long)b)&3 && len)){
  94                 do {
  95                         u8 *p = (u8 *)b;
  96                         DO_CRC(*p++);
  97                         b = (void *)p;
  98                 } while ((--len) && ((long)b)&3 );
  99         }
 100         if(likely(len >= 4)){
 101                 /* load data 32 bits wide, xor data 32 bits wide. */
 102                 size_t save_len = len & 3;
 103                 len = len >> 2;
 104                 --b; /* use pre increment below(*++b) for speed */
 105                 do {
 106                         crc ^= *++b;
 107                         DO_CRC(0);
 108                         DO_CRC(0);
 109                         DO_CRC(0);
 110                         DO_CRC(0);
 111                 } while (--len);
 112                 b++; /* point to next byte(s) */
 113                 len = save_len;
 114         }
 115         /* And the last few bytes */
 116         if(len){
 117                 do {
 118                         u8 *p = (u8 *)b;
 119                         DO_CRC(*p++);
 120                         b = (void *)p;
 121                 } while (--len);
 122         }
 123
 124         return __le32_to_cpu(crc);
 125 #undef ENDIAN_SHIFT
 126 #undef DO_CRC
 127
 128 # elif CRC_LE_BITS == 4
 129         while (len--) {
 130                 crc ^= *p++;
 131                 crc = (crc >> 4) ^ crc32table_le[crc & 15];
 132                 crc = (crc >> 4) ^ crc32table_le[crc & 15];
 133         }
 134         return crc;
 135 # elif CRC_LE_BITS == 2
 136         while (len--) {
 137                 crc ^= *p++;
 138                 crc = (crc >> 2) ^ crc32table_le[crc & 3];
 139                 crc = (crc >> 2) ^ crc32table_le[crc & 3];
 140                 crc = (crc >> 2) ^ crc32table_le[crc & 3];
 141                 crc = (crc >> 2) ^ crc32table_le[crc & 3];
 142         }
 143         return crc;
 144 # endif
 145 }
 146 #endif
 147
 148 #if CRC_BE_BITS == 1
 149 /*
 150  * In fact, the table-based code will work in this case, but it can be
 151  * simplified by inlining the table in ?: form.
 152  */
 153
 154 /**
 155  * crc32_be() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
 156  * @crc - seed value for computation.  ~0 for Ethernet, sometimes 0 for
 157  *        other uses, or the previous crc32 value if computing incrementally.
 158  * @p   - pointer to buffer over which CRC is run
 159  * @len - length of buffer @p
 160  *
 161  */
 162 u32 __attribute_pure__ crc32_be(u32 crc, unsigned char const *p, size_t len)
 163 {
 164         int i;
 165         while (len--) {
 166                 crc ^= *p++ << 24;
 167                 for (i = 0; i < 8; i++)
 168                         crc =
 169                             (crc << 1) ^ ((crc & 0x80000000) ? CRCPOLY_BE :
 170                                           0);
 171         }
 172         return crc;
 173 }
 174
 175 #else                           /* Table-based approach */
 176 /**
 177  * crc32_be() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
 178  * @crc - seed value for computation.  ~0 for Ethernet, sometimes 0 for
 179  *        other uses, or the previous crc32 value if computing incrementally.
 180  * @p   - pointer to buffer over which CRC is run
 181  * @len - length of buffer @p
 182  *
 183  */
 184 u32 __attribute_pure__ crc32_be(u32 crc, unsigned char const *p, size_t len)
 185 {
 186 # if CRC_BE_BITS == 8
 187         const u32      *b =(u32 *)p;
 188         const u32      *tab = crc32table_be;
 189
 190 # ifdef __LITTLE_ENDIAN
 191 #  define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8)
 192 # else
 193 #  define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8)
 194 # endif
 195
 196         crc = __cpu_to_be32(crc);
 197         /* Align it */
 198         if(unlikely(((long)b)&3 && len)){
 199                 do {
 200                         u8 *p = (u8 *)b;
 201                         DO_CRC(*p++);
 202                         b = (u32 *)p;
 203                 } while ((--len) && ((long)b)&3 );
 204         }
 205         if(likely(len >= 4)){
 206                 /* load data 32 bits wide, xor data 32 bits wide. */
 207                 size_t save_len = len & 3;
 208                 len = len >> 2;
 209                 --b; /* use pre increment below(*++b) for speed */
 210                 do {
 211                         crc ^= *++b;
 212                         DO_CRC(0);
 213                         DO_CRC(0);
 214                         DO_CRC(0);
 215                         DO_CRC(0);
 216                 } while (--len);
 217                 b++; /* point to next byte(s) */
 218                 len = save_len;
 219         }
 220         /* And the last few bytes */
 221         if(len){
 222                 do {
 223                         u8 *p = (u8 *)b;
 224                         DO_CRC(*p++);
 225                         b = (void *)p;
 226                 } while (--len);
 227         }
 228         return __be32_to_cpu(crc);
 229 #undef ENDIAN_SHIFT
 230 #undef DO_CRC
 231
 232 # elif CRC_BE_BITS == 4
 233         while (len--) {
 234                 crc ^= *p++ << 24;
 235                 crc = (crc << 4) ^ crc32table_be[crc >> 28];
 236                 crc = (crc << 4) ^ crc32table_be[crc >> 28];
 237         }
 238         return crc;
 239 # elif CRC_BE_BITS == 2
 240         while (len--) {
 241                 crc ^= *p++ << 24;
 242                 crc = (crc << 2) ^ crc32table_be[crc >> 30];
 243                 crc = (crc << 2) ^ crc32table_be[crc >> 30];
 244                 crc = (crc << 2) ^ crc32table_be[crc >> 30];
 245                 crc = (crc << 2) ^ crc32table_be[crc >> 30];
 246         }
 247         return crc;
 248 # endif
 249 }
 250 #endif
 251
 252 u32 bitreverse(u32 x)
 253 {
 254         x = (x >> 16) | (x << 16);
 255         x = (x >> 8 & 0x00ff00ff) | (x << 8 & 0xff00ff00);
 256         x = (x >> 4 & 0x0f0f0f0f) | (x << 4 & 0xf0f0f0f0);
 257         x = (x >> 2 & 0x33333333) | (x << 2 & 0xcccccccc);
 258         x = (x >> 1 & 0x55555555) | (x << 1 & 0xaaaaaaaa);
 259         return x;
 260 }
 261
 262 EXPORT_SYMBOL(crc32_le);
 263 EXPORT_SYMBOL(crc32_be);
 264 EXPORT_SYMBOL(bitreverse);
 265
 266 /*
 267  * A brief CRC tutorial.
 268  *
 269  * A CRC is a long-division remainder.  You add the CRC to the message,
 270  * and the whole thing (message+CRC) is a multiple of the given
 271  * CRC polynomial.  To check the CRC, you can either check that the
 272  * CRC matches the recomputed value, *or* you can check that the
 273  * remainder computed on the message+CRC is 0.  This latter approach
 274  * is used by a lot of hardware implementations, and is why so many
 275  * protocols put the end-of-frame flag after the CRC.
 276  *
 277  * It's actually the same long division you learned in school, except that
 278  * - We're working in binary, so the digits are only 0 and 1, and
 279  * - When dividing polynomials, there are no carries.  Rather than add and
 280  *   subtract, we just xor.  Thus, we tend to get a bit sloppy about
 281  *   the difference between adding and subtracting.
 282  *
 283  * A 32-bit CRC polynomial is actually 33 bits long.  But since it's
 284  * 33 bits long, bit 32 is always going to be set, so usually the CRC
 285  * is written in hex with the most significant bit omitted.  (If you're
 286  * familiar with the IEEE 754 floating-point format, it's the same idea.)
 287  *
 288  * Note that a CRC is computed over a string of *bits*, so you have
 289  * to decide on the endianness of the bits within each byte.  To get
 290  * the best error-detecting properties, this should correspond to the
 291  * order they're actually sent.  For example, standard RS-232 serial is
 292  * little-endian; the most significant bit (sometimes used for parity)
 293  * is sent last.  And when appending a CRC word to a message, you should
 294  * do it in the right order, matching the endianness.
 295  *
 296  * Just like with ordinary division, the remainder is always smaller than
 297  * the divisor (the CRC polynomial) you're dividing by.  Each step of the
 298  * division, you take one more digit (bit) of the dividend and append it
 299  * to the current remainder.  Then you figure out the appropriate multiple
 300  * of the divisor to subtract to being the remainder back into range.
 301  * In binary, it's easy - it has to be either 0 or 1, and to make the
 302  * XOR cancel, it's just a copy of bit 32 of the remainder.
 303  *
 304  * When computing a CRC, we don't care about the quotient, so we can
 305  * throw the quotient bit away, but subtract the appropriate multiple of
 306  * the polynomial from the remainder and we're back to where we started,
 307  * ready to process the next bit.
 308  *
 309  * A big-endian CRC written this way would be coded like:
 310  * for (i = 0; i < input_bits; i++) {
 311  *      multiple = remainder & 0x80000000 ? CRCPOLY : 0;
 312  *      remainder = (remainder << 1 | next_input_bit()) ^ multiple;
 313  * }
 314  * Notice how, to get at bit 32 of the shifted remainder, we look
 315  * at bit 31 of the remainder *before* shifting it.
 316  *
 317  * But also notice how the next_input_bit() bits we're shifting into
 318  * the remainder don't actually affect any decision-making until
 319  * 32 bits later.  Thus, the first 32 cycles of this are pretty boring.
 320  * Also, to add the CRC to a message, we need a 32-bit-long hole for it at
 321  * the end, so we have to add 32 extra cycles shifting in zeros at the
 322  * end of every message,
 323  *
 324  * So the standard trick is to rearrage merging in the next_input_bit()
 325  * until the moment it's needed.  Then the first 32 cycles can be precomputed,
 326  * and merging in the final 32 zero bits to make room for the CRC can be
 327  * skipped entirely.
 328  * This changes the code to:
 329  * for (i = 0; i < input_bits; i++) {
 330  *      remainder ^= next_input_bit() << 31;
 331  *      multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
 332  *      remainder = (remainder << 1) ^ multiple;
 333  * }
 334  * With this optimization, the little-endian code is simpler:
 335  * for (i = 0; i < input_bits; i++) {
 336  *      remainder ^= next_input_bit();
 337  *      multiple = (remainder & 1) ? CRCPOLY : 0;
 338  *      remainder = (remainder >> 1) ^ multiple;
 339  * }
 340  *
 341  * Note that the other details of endianness have been hidden in CRCPOLY
 342  * (which must be bit-reversed) and next_input_bit().
 343  *
 344  * However, as long as next_input_bit is returning the bits in a sensible
 345  * order, we can actually do the merging 8 or more bits at a time rather
 346  * than one bit at a time:
 347  * for (i = 0; i < input_bytes; i++) {
 348  *      remainder ^= next_input_byte() << 24;
 349  *      for (j = 0; j < 8; j++) {
 350  *              multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
 351  *              remainder = (remainder << 1) ^ multiple;
 352  *      }
 353  * }
 354  * Or in little-endian:
 355  * for (i = 0; i < input_bytes; i++) {
 356  *      remainder ^= next_input_byte();
 357  *      for (j = 0; j < 8; j++) {
 358  *              multiple = (remainder & 1) ? CRCPOLY : 0;
 359  *              remainder = (remainder << 1) ^ multiple;
 360  *      }
 361  * }
 362  * If the input is a multiple of 32 bits, you can even XOR in a 32-bit
 363  * word at a time and increase the inner loop count to 32.
 364  *
 365  * You can also mix and match the two loop styles, for example doing the
 366  * bulk of a message byte-at-a-time and adding bit-at-a-time processing
 367  * for any fractional bytes at the end.
 368  *
 369  * The only remaining optimization is to the byte-at-a-time table method.
 370  * Here, rather than just shifting one bit of the remainder to decide
 371  * in the correct multiple to subtract, we can shift a byte at a time.
 372  * This produces a 40-bit (rather than a 33-bit) intermediate remainder,
 373  * but again the multiple of the polynomial to subtract depends only on
 374  * the high bits, the high 8 bits in this case.
 375  *
 376  * The multile we need in that case is the low 32 bits of a 40-bit
 377  * value whose high 8 bits are given, and which is a multiple of the
 378  * generator polynomial.  This is simply the CRC-32 of the given
 379  * one-byte message.
 380  *
 381  * Two more details: normally, appending zero bits to a message which
 382  * is already a multiple of a polynomial produces a larger multiple of that
 383  * polynomial.  To enable a CRC to detect this condition, it's common to
 384  * invert the CRC before appending it.  This makes the remainder of the
 385  * message+crc come out not as zero, but some fixed non-zero value.
 386  *
 387  * The same problem applies to zero bits prepended to the message, and
 388  * a similar solution is used.  Instead of starting with a remainder of
 389  * 0, an initial remainder of all ones is used.  As long as you start
 390  * the same way on decoding, it doesn't make a difference.
 391  */
 392
 393 #ifdef UNITTEST
 394
 395 #include <stdlib.h>
 396 #include <stdio.h>
 397
 398 #if 0                           /*Not used at present */
 399 static void
 400 buf_dump(char const *prefix, unsigned char const *buf, size_t len)
 401 {
 402         fputs(prefix, stdout);
 403         while (len--)
 404                 printf(" %02x", *buf++);
 405         putchar('\n');
 406
 407 }
 408 #endif
 409
 410 static void bytereverse(unsigned char *buf, size_t len)
 411 {
 412         while (len--) {
 413                 unsigned char x = *buf;
 414                 x = (x >> 4) | (x << 4);
 415                 x = (x >> 2 & 0x33) | (x << 2 & 0xcc);
 416                 x = (x >> 1 & 0x55) | (x << 1 & 0xaa);
 417                 *buf++ = x;
 418         }
 419 }
 420
 421 static void random_garbage(unsigned char *buf, size_t len)
 422 {
 423         while (len--)
 424                 *buf++ = (unsigned char) random();
 425 }
 426
 427 #if 0                           /* Not used at present */
 428 static void store_le(u32 x, unsigned char *buf)
 429 {
 430         buf[0] = (unsigned char) x;
 431         buf[1] = (unsigned char) (x >> 8);
 432         buf[2] = (unsigned char) (x >> 16);
 433         buf[3] = (unsigned char) (x >> 24);
 434 }
 435 #endif
 436
 437 static void store_be(u32 x, unsigned char *buf)
 438 {
 439         buf[0] = (unsigned char) (x >> 24);
 440         buf[1] = (unsigned char) (x >> 16);
 441         buf[2] = (unsigned char) (x >> 8);
 442         buf[3] = (unsigned char) x;
 443 }
 444
 445 /*
 446  * This checks that CRC(buf + CRC(buf)) = 0, and that
 447  * CRC commutes with bit-reversal.  This has the side effect
 448  * of bytewise bit-reversing the input buffer, and returns
 449  * the CRC of the reversed buffer.
 450  */
 451 static u32 test_step(u32 init, unsigned char *buf, size_t len)
 452 {
 453         u32 crc1, crc2;
 454         size_t i;
 455
 456         crc1 = crc32_be(init, buf, len);
 457         store_be(crc1, buf + len);
 458         crc2 = crc32_be(init, buf, len + 4);
 459         if (crc2)
 460                 printf("\nCRC cancellation fail: 0x%08x should be 0\n",
 461                        crc2);
 462
 463         for (i = 0; i <= len + 4; i++) {
 464                 crc2 = crc32_be(init, buf, i);
 465                 crc2 = crc32_be(crc2, buf + i, len + 4 - i);
 466                 if (crc2)
 467                         printf("\nCRC split fail: 0x%08x\n", crc2);
 468         }
 469
 470         /* Now swap it around for the other test */
 471
 472         bytereverse(buf, len + 4);
 473         init = bitreverse(init);
 474         crc2 = bitreverse(crc1);
 475         if (crc1 != bitreverse(crc2))
 476                 printf("\nBit reversal fail: 0x%08x -> %0x08x -> 0x%08x\n",
 477                        crc1, crc2, bitreverse(crc2));
 478         crc1 = crc32_le(init, buf, len);
 479         if (crc1 != crc2)
 480                 printf("\nCRC endianness fail: 0x%08x != 0x%08x\n", crc1,
 481                        crc2);
 482         crc2 = crc32_le(init, buf, len + 4);
 483         if (crc2)
 484                 printf("\nCRC cancellation fail: 0x%08x should be 0\n",
 485                        crc2);
 486
 487         for (i = 0; i <= len + 4; i++) {
 488                 crc2 = crc32_le(init, buf, i);
 489                 crc2 = crc32_le(crc2, buf + i, len + 4 - i);
 490                 if (crc2)
 491                         printf("\nCRC split fail: 0x%08x\n", crc2);
 492         }
 493
 494         return crc1;
 495 }
 496
 497 #define SIZE 64
 498 #define INIT1 0
 499 #define INIT2 0
 500
 501 int main(void)
 502 {
 503         unsigned char buf1[SIZE + 4];
 504         unsigned char buf2[SIZE + 4];
 505         unsigned char buf3[SIZE + 4];
 506         int i, j;
 507         u32 crc1, crc2, crc3;
 508
 509         for (i = 0; i <= SIZE; i++) {
 510                 printf("\rTesting length %d...", i);
 511                 fflush(stdout);
 512                 random_garbage(buf1, i);
 513                 random_garbage(buf2, i);
 514                 for (j = 0; j < i; j++)
 515                         buf3[j] = buf1[j] ^ buf2[j];
 516
 517                 crc1 = test_step(INIT1, buf1, i);
 518                 crc2 = test_step(INIT2, buf2, i);
 519                 /* Now check that CRC(buf1 ^ buf2) = CRC(buf1) ^ CRC(buf2) */
 520                 crc3 = test_step(INIT1 ^ INIT2, buf3, i);
 521                 if (crc3 != (crc1 ^ crc2))
 522                         printf("CRC XOR fail: 0x%08x != 0x%08x ^ 0x%08x\n",
 523                                crc3, crc1, crc2);
 524         }
 525         printf("\nAll test complete.  No failures expected.\n");
 526         return 0;
 527 }
 528
 529 #endif                          /* UNITTEST */