lib/crc32.c

   1 /*
   2  * Aug 8, 2011 Bob Pearson with help from Joakim Tjernlund and George Spelvin
   3  * cleaned up code to current version of sparse and added the slicing-by-8
   4  * algorithm to the closely similar existing slicing-by-4 algorithm.
   5  *
   6  * Oct 15, 2000 Matt Domsch <Matt_Domsch@dell.com>
   7  * Nicer crc32 functions/docs submitted by linux@horizon.com.  Thanks!
   8  * Code was from the public domain, copyright abandoned.  Code was
   9  * subsequently included in the kernel, thus was re-licensed under the
  10  * GNU GPL v2.
  11  *
  12  * Oct 12, 2000 Matt Domsch <Matt_Domsch@dell.com>
  13  * Same crc32 function was used in 5 other places in the kernel.
  14  * I made one version, and deleted the others.
  15  * There are various incantations of crc32().  Some use a seed of 0 or ~0.
  16  * Some xor at the end with ~0.  The generic crc32() function takes
  17  * seed as an argument, and doesn't xor at the end.  Then individual
  18  * users can do whatever they need.
  19  *   drivers/net/smc9194.c uses seed ~0, doesn't xor with ~0.
  20  *   fs/jffs2 uses seed 0, doesn't xor with ~0.
  21  *   fs/partitions/efi.c uses seed ~0, xor's with ~0.
  22  *
  23  * This source code is licensed under the GNU General Public License,
  24  * Version 2.  See the file COPYING for more details.
  25  */
  26
  27 /* see: Documentation/crc32.txt for a description of algorithms */
  28
  29 #include <linux/crc32.h>
  30 #include <linux/module.h>
  31 #include <linux/types.h>
  32 #include <linux/sched.h>
  33 #include "crc32defs.h"
  34
  35 #if CRC_LE_BITS > 8
  36 # define tole(x) ((__force u32) cpu_to_le32(x))
  37 #else
  38 # define tole(x) (x)
  39 #endif
  40
  41 #if CRC_BE_BITS > 8
  42 # define tobe(x) ((__force u32) cpu_to_be32(x))
  43 #else
  44 # define tobe(x) (x)
  45 #endif
  46
  47 #include "crc32table.h"
  48
  49 MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
  50 MODULE_DESCRIPTION("Various CRC32 calculations");
  51 MODULE_LICENSE("GPL");
  52
  53 #if CRC_LE_BITS > 8 || CRC_BE_BITS > 8
  54
  55 /* implements slicing-by-4 or slicing-by-8 algorithm */
  56 static inline u32 __pure
  57 crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256])
  58 {
  59 # ifdef __LITTLE_ENDIAN
  60 #  define DO_CRC(x) crc = t0[(crc ^ (x)) & 255] ^ (crc >> 8)
  61 #  define DO_CRC4 (t3[(q) & 255] ^ t2[(q >> 8) & 255] ^ \
  62                    t1[(q >> 16) & 255] ^ t0[(q >> 24) & 255])
  63 #  define DO_CRC8 (t7[(q) & 255] ^ t6[(q >> 8) & 255] ^ \
  64                    t5[(q >> 16) & 255] ^ t4[(q >> 24) & 255])
  65 # else
  66 #  define DO_CRC(x) crc = t0[((crc >> 24) ^ (x)) & 255] ^ (crc << 8)
  67 #  define DO_CRC4 (t0[(q) & 255] ^ t1[(q >> 8) & 255] ^ \
  68                    t2[(q >> 16) & 255] ^ t3[(q >> 24) & 255])
  69 #  define DO_CRC8 (t4[(q) & 255] ^ t5[(q >> 8) & 255] ^ \
  70                    t6[(q >> 16) & 255] ^ t7[(q >> 24) & 255])
  71 # endif
  72         const u32 *b;
  73         size_t    rem_len;
  74 # ifdef CONFIG_X86
  75         size_t i;
  76 # endif
  77         const u32 *t0=tab[0], *t1=tab[1], *t2=tab[2], *t3=tab[3];
  78 # if CRC_LE_BITS != 32
  79         const u32 *t4 = tab[4], *t5 = tab[5], *t6 = tab[6], *t7 = tab[7];
  80 # endif
  81         u32 q;
  82
  83         /* Align it */
  84         if (unlikely((long)buf & 3 && len)) {
  85                 do {
  86                         DO_CRC(*buf++);
  87                 } while ((--len) && ((long)buf)&3);
  88         }
  89
  90 # if CRC_LE_BITS == 32
  91         rem_len = len & 3;
  92         len = len >> 2;
  93 # else
  94         rem_len = len & 7;
  95         len = len >> 3;
  96 # endif
  97
  98         b = (const u32 *)buf;
  99 # ifdef CONFIG_X86
 100         --b;
 101         for (i = 0; i < len; i++) {
 102 # else
 103         for (--b; len; --len) {
 104 # endif
 105                 q = crc ^ *++b; /* use pre increment for speed */
 106 # if CRC_LE_BITS == 32
 107                 crc = DO_CRC4;
 108 # else
 109                 crc = DO_CRC8;
 110                 q = *++b;
 111                 crc ^= DO_CRC4;
 112 # endif
 113         }
 114         len = rem_len;
 115         /* And the last few bytes */
 116         if (len) {
 117                 u8 *p = (u8 *)(b + 1) - 1;
 118 # ifdef CONFIG_X86
 119                 for (i = 0; i < len; i++)
 120                         DO_CRC(*++p); /* use pre increment for speed */
 121 # else
 122                 do {
 123                         DO_CRC(*++p); /* use pre increment for speed */
 124                 } while (--len);
 125 # endif
 126         }
 127         return crc;
 128 #undef DO_CRC
 129 #undef DO_CRC4
 130 #undef DO_CRC8
 131 }
 132 #endif
 133
 134
 135 /**
 136  * crc32_le_generic() - Calculate bitwise little-endian Ethernet AUTODIN II
 137  *                      CRC32/CRC32C
 138  * @crc: seed value for computation.  ~0 for Ethernet, sometimes 0 for other
 139  *       uses, or the previous crc32/crc32c value if computing incrementally.
 140  * @p: pointer to buffer over which CRC32/CRC32C is run
 141  * @len: length of buffer @p
 142  * @tab: little-endian Ethernet table
 143  * @polynomial: CRC32/CRC32c LE polynomial
 144  */
 145 static inline u32 __pure crc32_le_generic(u32 crc, unsigned char const *p,
 146                                           size_t len, const u32 (*tab)[256],
 147                                           u32 polynomial)
 148 {
 149 #if CRC_LE_BITS == 1
 150         int i;
 151         while (len--) {
 152                 crc ^= *p++;
 153                 for (i = 0; i < 8; i++)
 154                         crc = (crc >> 1) ^ ((crc & 1) ? polynomial : 0);
 155         }
 156 # elif CRC_LE_BITS == 2
 157         while (len--) {
 158                 crc ^= *p++;
 159                 crc = (crc >> 2) ^ tab[0][crc & 3];
 160                 crc = (crc >> 2) ^ tab[0][crc & 3];
 161                 crc = (crc >> 2) ^ tab[0][crc & 3];
 162                 crc = (crc >> 2) ^ tab[0][crc & 3];
 163         }
 164 # elif CRC_LE_BITS == 4
 165         while (len--) {
 166                 crc ^= *p++;
 167                 crc = (crc >> 4) ^ tab[0][crc & 15];
 168                 crc = (crc >> 4) ^ tab[0][crc & 15];
 169         }
 170 # elif CRC_LE_BITS == 8
 171         /* aka Sarwate algorithm */
 172         while (len--) {
 173                 crc ^= *p++;
 174                 crc = (crc >> 8) ^ tab[0][crc & 255];
 175         }
 176 # else
 177         crc = (__force u32) __cpu_to_le32(crc);
 178         crc = crc32_body(crc, p, len, tab);
 179         crc = __le32_to_cpu((__force __le32)crc);
 180 #endif
 181         return crc;
 182 }
 183
 184 #if CRC_LE_BITS == 1
 185 u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
 186 {
 187         return crc32_le_generic(crc, p, len, NULL, CRCPOLY_LE);
 188 }
 189 u32 __pure __crc32c_le(u32 crc, unsigned char const *p, size_t len)
 190 {
 191         return crc32_le_generic(crc, p, len, NULL, CRC32C_POLY_LE);
 192 }
 193 #else
 194 u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
 195 {
 196         return crc32_le_generic(crc, p, len,
 197                         (const u32 (*)[256])crc32table_le, CRCPOLY_LE);
 198 }
 199 u32 __pure __crc32c_le(u32 crc, unsigned char const *p, size_t len)
 200 {
 201         return crc32_le_generic(crc, p, len,
 202                         (const u32 (*)[256])crc32ctable_le, CRC32C_POLY_LE);
 203 }
 204 #endif
 205 EXPORT_SYMBOL(crc32_le);
 206 EXPORT_SYMBOL(__crc32c_le);
 207
 208 /*
 209  * This multiplies the polynomials x and y modulo the given modulus.
 210  * This follows the "little-endian" CRC convention that the lsbit
 211  * represents the highest power of x, and the msbit represents x^0.
 212  */
 213 static u32 __attribute_const__ gf2_multiply(u32 x, u32 y, u32 modulus)
 214 {
 215         u32 product = x & 1 ? y : 0;
 216         int i;
 217
 218         for (i = 0; i < 31; i++) {
 219                 product = (product >> 1) ^ (product & 1 ? modulus : 0);
 220                 x >>= 1;
 221                 product ^= x & 1 ? y : 0;
 222         }
 223
 224         return product;
 225 }
 226
 227 /**
 228  * crc32_generic_shift - Append @len 0 bytes to crc, in logarithmic time
 229  * @crc: The original little-endian CRC (i.e. lsbit is x^31 coefficient)
 230  * @len: The number of bytes. @crc is multiplied by x^(8*@len)
 231  * @polynomial: The modulus used to reduce the result to 32 bits.
 232  *
 233  * It's possible to parallelize CRC computations by computing a CRC
 234  * over separate ranges of a buffer, then summing them.
 235  * This shifts the given CRC by 8*len bits (i.e. produces the same effect
 236  * as appending len bytes of zero to the data), in time proportional
 237  * to log(len).
 238  */
 239 static u32 __attribute_const__ crc32_generic_shift(u32 crc, size_t len,
 240                                                    u32 polynomial)
 241 {
 242         u32 power = polynomial; /* CRC of x^32 */
 243         int i;
 244
 245         /* Shift up to 32 bits in the simple linear way */
 246         for (i = 0; i < 8 * (int)(len & 3); i++)
 247                 crc = (crc >> 1) ^ (crc & 1 ? polynomial : 0);
 248
 249         len >>= 2;
 250         if (!len)
 251                 return crc;
 252
 253         for (;;) {
 254                 /* "power" is x^(2^i), modulo the polynomial */
 255                 if (len & 1)
 256                         crc = gf2_multiply(crc, power, polynomial);
 257
 258                 len >>= 1;
 259                 if (!len)
 260                         break;
 261
 262                 /* Square power, advancing to x^(2^(i+1)) */
 263                 power = gf2_multiply(power, power, polynomial);
 264         }
 265
 266         return crc;
 267 }
 268
 269 u32 __attribute_const__ crc32_le_shift(u32 crc, size_t len)
 270 {
 271         return crc32_generic_shift(crc, len, CRCPOLY_LE);
 272 }
 273
 274 u32 __attribute_const__ __crc32c_le_shift(u32 crc, size_t len)
 275 {
 276         return crc32_generic_shift(crc, len, CRC32C_POLY_LE);
 277 }
 278 EXPORT_SYMBOL(crc32_le_shift);
 279 EXPORT_SYMBOL(__crc32c_le_shift);
 280
 281 /**
 282  * crc32_be_generic() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
 283  * @crc: seed value for computation.  ~0 for Ethernet, sometimes 0 for
 284  *      other uses, or the previous crc32 value if computing incrementally.
 285  * @p: pointer to buffer over which CRC32 is run
 286  * @len: length of buffer @p
 287  * @tab: big-endian Ethernet table
 288  * @polynomial: CRC32 BE polynomial
 289  */
 290 static inline u32 __pure crc32_be_generic(u32 crc, unsigned char const *p,
 291                                           size_t len, const u32 (*tab)[256],
 292                                           u32 polynomial)
 293 {
 294 #if CRC_BE_BITS == 1
 295         int i;
 296         while (len--) {
 297                 crc ^= *p++ << 24;
 298                 for (i = 0; i < 8; i++)
 299                         crc =
 300                             (crc << 1) ^ ((crc & 0x80000000) ? polynomial :
 301                                           0);
 302         }
 303 # elif CRC_BE_BITS == 2
 304         while (len--) {
 305                 crc ^= *p++ << 24;
 306                 crc = (crc << 2) ^ tab[0][crc >> 30];
 307                 crc = (crc << 2) ^ tab[0][crc >> 30];
 308                 crc = (crc << 2) ^ tab[0][crc >> 30];
 309                 crc = (crc << 2) ^ tab[0][crc >> 30];
 310         }
 311 # elif CRC_BE_BITS == 4
 312         while (len--) {
 313                 crc ^= *p++ << 24;
 314                 crc = (crc << 4) ^ tab[0][crc >> 28];
 315                 crc = (crc << 4) ^ tab[0][crc >> 28];
 316         }
 317 # elif CRC_BE_BITS == 8
 318         while (len--) {
 319                 crc ^= *p++ << 24;
 320                 crc = (crc << 8) ^ tab[0][crc >> 24];
 321         }
 322 # else
 323         crc = (__force u32) __cpu_to_be32(crc);
 324         crc = crc32_body(crc, p, len, tab);
 325         crc = __be32_to_cpu((__force __be32)crc);
 326 # endif
 327         return crc;
 328 }
 329
 330 #if CRC_LE_BITS == 1
 331 u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
 332 {
 333         return crc32_be_generic(crc, p, len, NULL, CRCPOLY_BE);
 334 }
 335 #else
 336 u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
 337 {
 338         return crc32_be_generic(crc, p, len,
 339                         (const u32 (*)[256])crc32table_be, CRCPOLY_BE);
 340 }
 341 #endif
 342 EXPORT_SYMBOL(crc32_be);