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); 343