root/lib/crc32.c

DEFINITIONS

1. crc32_body
2. crc32_le_generic
3. crc32_le
4. __crc32c_le
5. crc32_le
6. __crc32c_le
7. crc32_le_base
8. crc32_generic_shift
9. crc32_le_shift
10. __crc32c_le_shift
11. crc32_be_generic
12. crc32_be
13. crc32_be

   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/crc32poly.h>
  31 #include <linux/module.h>
  32 #include <linux/types.h>
  33 #include <linux/sched.h>
  34 #include "crc32defs.h"
  35 
  36 #if CRC_LE_BITS > 8
  37 # define tole(x) ((__force u32) cpu_to_le32(x))
  38 #else
  39 # define tole(x) (x)
  40 #endif
  41 
  42 #if CRC_BE_BITS > 8
  43 # define tobe(x) ((__force u32) cpu_to_be32(x))
  44 #else
  45 # define tobe(x) (x)
  46 #endif
  47 
  48 #include "crc32table.h"
  49 
  50 MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
  51 MODULE_DESCRIPTION("Various CRC32 calculations");
  52 MODULE_LICENSE("GPL");
  53 
  54 #if CRC_LE_BITS > 8 || CRC_BE_BITS > 8
  55 
  56 /* implements slicing-by-4 or slicing-by-8 algorithm */
  57 static inline u32 __pure
  58 crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256])
  59 {
  60 # ifdef __LITTLE_ENDIAN
  61 #  define DO_CRC(x) crc = t0[(crc ^ (x)) & 255] ^ (crc >> 8)
  62 #  define DO_CRC4 (t3[(q) & 255] ^ t2[(q >> 8) & 255] ^ \
  63                    t1[(q >> 16) & 255] ^ t0[(q >> 24) & 255])
  64 #  define DO_CRC8 (t7[(q) & 255] ^ t6[(q >> 8) & 255] ^ \
  65                    t5[(q >> 16) & 255] ^ t4[(q >> 24) & 255])
  66 # else
  67 #  define DO_CRC(x) crc = t0[((crc >> 24) ^ (x)) & 255] ^ (crc << 8)
  68 #  define DO_CRC4 (t0[(q) & 255] ^ t1[(q >> 8) & 255] ^ \
  69                    t2[(q >> 16) & 255] ^ t3[(q >> 24) & 255])
  70 #  define DO_CRC8 (t4[(q) & 255] ^ t5[(q >> 8) & 255] ^ \
  71                    t6[(q >> 16) & 255] ^ t7[(q >> 24) & 255])
  72 # endif
  73         const u32 *b;
  74         size_t    rem_len;
  75 # ifdef CONFIG_X86
  76         size_t i;
  77 # endif
  78         const u32 *t0=tab[0], *t1=tab[1], *t2=tab[2], *t3=tab[3];
  79 # if CRC_LE_BITS != 32
  80         const u32 *t4 = tab[4], *t5 = tab[5], *t6 = tab[6], *t7 = tab[7];
  81 # endif
  82         u32 q;
  83 
  84         /* Align it */
  85         if (unlikely((long)buf & 3 && len)) {
  86                 do {
  87                         DO_CRC(*buf++);
  88                 } while ((--len) && ((long)buf)&3);
  89         }
  90 
  91 # if CRC_LE_BITS == 32
  92         rem_len = len & 3;
  93         len = len >> 2;
  94 # else
  95         rem_len = len & 7;
  96         len = len >> 3;
  97 # endif
  98 
  99         b = (const u32 *)buf;
 100 # ifdef CONFIG_X86
 101         --b;
 102         for (i = 0; i < len; i++) {
 103 # else
 104         for (--b; len; --len) {
 105 # endif
 106                 q = crc ^ *++b; /* use pre increment for speed */
 107 # if CRC_LE_BITS == 32
 108                 crc = DO_CRC4;
 109 # else
 110                 crc = DO_CRC8;
 111                 q = *++b;
 112                 crc ^= DO_CRC4;
 113 # endif
 114         }
 115         len = rem_len;
 116         /* And the last few bytes */
 117         if (len) {
 118                 u8 *p = (u8 *)(b + 1) - 1;
 119 # ifdef CONFIG_X86
 120                 for (i = 0; i < len; i++)
 121                         DO_CRC(*++p); /* use pre increment for speed */
 122 # else
 123                 do {
 124                         DO_CRC(*++p); /* use pre increment for speed */
 125                 } while (--len);
 126 # endif
 127         }
 128         return crc;
 129 #undef DO_CRC
 130 #undef DO_CRC4
 131 #undef DO_CRC8
 132 }
 133 #endif
 134 
 135 
 136 /**
 137  * crc32_le_generic() - Calculate bitwise little-endian Ethernet AUTODIN II
 138  *                      CRC32/CRC32C
 139  * @crc: seed value for computation.  ~0 for Ethernet, sometimes 0 for other
 140  *       uses, or the previous crc32/crc32c value if computing incrementally.
 141  * @p: pointer to buffer over which CRC32/CRC32C is run
 142  * @len: length of buffer @p
 143  * @tab: little-endian Ethernet table
 144  * @polynomial: CRC32/CRC32c LE polynomial
 145  */
 146 static inline u32 __pure crc32_le_generic(u32 crc, unsigned char const *p,
 147                                           size_t len, const u32 (*tab)[256],
 148                                           u32 polynomial)
 149 {
 150 #if CRC_LE_BITS == 1
 151         int i;
 152         while (len--) {
 153                 crc ^= *p++;
 154                 for (i = 0; i < 8; i++)
 155                         crc = (crc >> 1) ^ ((crc & 1) ? polynomial : 0);
 156         }
 157 # elif CRC_LE_BITS == 2
 158         while (len--) {
 159                 crc ^= *p++;
 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                 crc = (crc >> 2) ^ tab[0][crc & 3];
 164         }
 165 # elif CRC_LE_BITS == 4
 166         while (len--) {
 167                 crc ^= *p++;
 168                 crc = (crc >> 4) ^ tab[0][crc & 15];
 169                 crc = (crc >> 4) ^ tab[0][crc & 15];
 170         }
 171 # elif CRC_LE_BITS == 8
 172         /* aka Sarwate algorithm */
 173         while (len--) {
 174                 crc ^= *p++;
 175                 crc = (crc >> 8) ^ tab[0][crc & 255];
 176         }
 177 # else
 178         crc = (__force u32) __cpu_to_le32(crc);
 179         crc = crc32_body(crc, p, len, tab);
 180         crc = __le32_to_cpu((__force __le32)crc);
 181 #endif
 182         return crc;
 183 }
 184 
 185 #if CRC_LE_BITS == 1
 186 u32 __pure __weak crc32_le(u32 crc, unsigned char const *p, size_t len)
 187 {
 188         return crc32_le_generic(crc, p, len, NULL, CRC32_POLY_LE);
 189 }
 190 u32 __pure __weak __crc32c_le(u32 crc, unsigned char const *p, size_t len)
 191 {
 192         return crc32_le_generic(crc, p, len, NULL, CRC32C_POLY_LE);
 193 }
 194 #else
 195 u32 __pure __weak crc32_le(u32 crc, unsigned char const *p, size_t len)
 196 {
 197         return crc32_le_generic(crc, p, len,
 198                         (const u32 (*)[256])crc32table_le, CRC32_POLY_LE);
 199 }
 200 u32 __pure __weak __crc32c_le(u32 crc, unsigned char const *p, size_t len)
 201 {
 202         return crc32_le_generic(crc, p, len,
 203                         (const u32 (*)[256])crc32ctable_le, CRC32C_POLY_LE);
 204 }
 205 #endif
 206 EXPORT_SYMBOL(crc32_le);
 207 EXPORT_SYMBOL(__crc32c_le);
 208 
 209 u32 __pure crc32_le_base(u32, unsigned char const *, size_t) __alias(crc32_le);
 210 u32 __pure __crc32c_le_base(u32, unsigned char const *, size_t) __alias(__crc32c_le);
 211 
 212 /*
 213  * This multiplies the polynomials x and y modulo the given modulus.
 214  * This follows the "little-endian" CRC convention that the lsbit
 215  * represents the highest power of x, and the msbit represents x^0.
 216  */
 217 static u32 __attribute_const__ gf2_multiply(u32 x, u32 y, u32 modulus)
 218 {
 219         u32 product = x & 1 ? y : 0;
 220         int i;
 221 
 222         for (i = 0; i < 31; i++) {
 223                 product = (product >> 1) ^ (product & 1 ? modulus : 0);
 224                 x >>= 1;
 225                 product ^= x & 1 ? y : 0;
 226         }
 227 
 228         return product;
 229 }
 230 
 231 /**
 232  * crc32_generic_shift - Append @len 0 bytes to crc, in logarithmic time
 233  * @crc: The original little-endian CRC (i.e. lsbit is x^31 coefficient)
 234  * @len: The number of bytes. @crc is multiplied by x^(8*@len)
 235  * @polynomial: The modulus used to reduce the result to 32 bits.
 236  *
 237  * It's possible to parallelize CRC computations by computing a CRC
 238  * over separate ranges of a buffer, then summing them.
 239  * This shifts the given CRC by 8*len bits (i.e. produces the same effect
 240  * as appending len bytes of zero to the data), in time proportional
 241  * to log(len).
 242  */
 243 static u32 __attribute_const__ crc32_generic_shift(u32 crc, size_t len,
 244                                                    u32 polynomial)
 245 {
 246         u32 power = polynomial; /* CRC of x^32 */
 247         int i;
 248 
 249         /* Shift up to 32 bits in the simple linear way */
 250         for (i = 0; i < 8 * (int)(len & 3); i++)
 251                 crc = (crc >> 1) ^ (crc & 1 ? polynomial : 0);
 252 
 253         len >>= 2;
 254         if (!len)
 255                 return crc;
 256 
 257         for (;;) {
 258                 /* "power" is x^(2^i), modulo the polynomial */
 259                 if (len & 1)
 260                         crc = gf2_multiply(crc, power, polynomial);
 261 
 262                 len >>= 1;
 263                 if (!len)
 264                         break;
 265 
 266                 /* Square power, advancing to x^(2^(i+1)) */
 267                 power = gf2_multiply(power, power, polynomial);
 268         }
 269 
 270         return crc;
 271 }
 272 
 273 u32 __attribute_const__ crc32_le_shift(u32 crc, size_t len)
 274 {
 275         return crc32_generic_shift(crc, len, CRC32_POLY_LE);
 276 }
 277 
 278 u32 __attribute_const__ __crc32c_le_shift(u32 crc, size_t len)
 279 {
 280         return crc32_generic_shift(crc, len, CRC32C_POLY_LE);
 281 }
 282 EXPORT_SYMBOL(crc32_le_shift);
 283 EXPORT_SYMBOL(__crc32c_le_shift);
 284 
 285 /**
 286  * crc32_be_generic() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
 287  * @crc: seed value for computation.  ~0 for Ethernet, sometimes 0 for
 288  *      other uses, or the previous crc32 value if computing incrementally.
 289  * @p: pointer to buffer over which CRC32 is run
 290  * @len: length of buffer @p
 291  * @tab: big-endian Ethernet table
 292  * @polynomial: CRC32 BE polynomial
 293  */
 294 static inline u32 __pure crc32_be_generic(u32 crc, unsigned char const *p,
 295                                           size_t len, const u32 (*tab)[256],
 296                                           u32 polynomial)
 297 {
 298 #if CRC_BE_BITS == 1
 299         int i;
 300         while (len--) {
 301                 crc ^= *p++ << 24;
 302                 for (i = 0; i < 8; i++)
 303                         crc =
 304                             (crc << 1) ^ ((crc & 0x80000000) ? polynomial :
 305                                           0);
 306         }
 307 # elif CRC_BE_BITS == 2
 308         while (len--) {
 309                 crc ^= *p++ << 24;
 310                 crc = (crc << 2) ^ tab[0][crc >> 30];
 311                 crc = (crc << 2) ^ tab[0][crc >> 30];
 312                 crc = (crc << 2) ^ tab[0][crc >> 30];
 313                 crc = (crc << 2) ^ tab[0][crc >> 30];
 314         }
 315 # elif CRC_BE_BITS == 4
 316         while (len--) {
 317                 crc ^= *p++ << 24;
 318                 crc = (crc << 4) ^ tab[0][crc >> 28];
 319                 crc = (crc << 4) ^ tab[0][crc >> 28];
 320         }
 321 # elif CRC_BE_BITS == 8
 322         while (len--) {
 323                 crc ^= *p++ << 24;
 324                 crc = (crc << 8) ^ tab[0][crc >> 24];
 325         }
 326 # else
 327         crc = (__force u32) __cpu_to_be32(crc);
 328         crc = crc32_body(crc, p, len, tab);
 329         crc = __be32_to_cpu((__force __be32)crc);
 330 # endif
 331         return crc;
 332 }
 333 
 334 #if CRC_LE_BITS == 1
 335 u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
 336 {
 337         return crc32_be_generic(crc, p, len, NULL, CRC32_POLY_BE);
 338 }
 339 #else
 340 u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
 341 {
 342         return crc32_be_generic(crc, p, len,
 343                         (const u32 (*)[256])crc32table_be, CRC32_POLY_BE);
 344 }
 345 #endif
 346 EXPORT_SYMBOL(crc32_be);