diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/crc32.c | 147 |
1 files changed, 70 insertions, 77 deletions
diff --git a/lib/crc32.c b/lib/crc32.c index 21a7b2135..9af30ff 100644 --- a/lib/crc32.c +++ b/lib/crc32.c @@ -50,30 +50,6 @@ MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>"); MODULE_DESCRIPTION("Various CRC32 calculations"); MODULE_LICENSE("GPL"); -#define GF2_DIM 32 - -static u32 gf2_matrix_times(u32 *mat, u32 vec) -{ - u32 sum = 0; - - while (vec) { - if (vec & 1) - sum ^= *mat; - vec >>= 1; - mat++; - } - - return sum; -} - -static void gf2_matrix_square(u32 *square, u32 *mat) -{ - int i; - - for (i = 0; i < GF2_DIM; i++) - square[i] = gf2_matrix_times(mat, mat[i]); -} - #if CRC_LE_BITS > 8 || CRC_BE_BITS > 8 /* implements slicing-by-4 or slicing-by-8 algorithm */ @@ -155,51 +131,6 @@ crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256]) } #endif -/* For conditions of distribution and use, see copyright notice in zlib.h */ -static u32 crc32_generic_combine(u32 crc1, u32 crc2, size_t len2, - u32 polynomial) -{ - u32 even[GF2_DIM]; /* Even-power-of-two zeros operator */ - u32 odd[GF2_DIM]; /* Odd-power-of-two zeros operator */ - u32 row; - int i; - - if (len2 <= 0) - return crc1; - - /* Put operator for one zero bit in odd */ - odd[0] = polynomial; - row = 1; - for (i = 1; i < GF2_DIM; i++) { - odd[i] = row; - row <<= 1; - } - - gf2_matrix_square(even, odd); /* Put operator for two zero bits in even */ - gf2_matrix_square(odd, even); /* Put operator for four zero bits in odd */ - - /* Apply len2 zeros to crc1 (first square will put the operator for one - * zero byte, eight zero bits, in even). - */ - do { - /* Apply zeros operator for this bit of len2 */ - gf2_matrix_square(even, odd); - if (len2 & 1) - crc1 = gf2_matrix_times(even, crc1); - len2 >>= 1; - /* If no more bits set, then done */ - if (len2 == 0) - break; - /* Another iteration of the loop with odd and even swapped */ - gf2_matrix_square(odd, even); - if (len2 & 1) - crc1 = gf2_matrix_times(odd, crc1); - len2 >>= 1; - } while (len2 != 0); - - crc1 ^= crc2; - return crc1; -} /** * crc32_le_generic() - Calculate bitwise little-endian Ethernet AUTODIN II @@ -271,19 +202,81 @@ u32 __pure __crc32c_le(u32 crc, unsigned char const *p, size_t len) (const u32 (*)[256])crc32ctable_le, CRC32C_POLY_LE); } #endif -u32 __pure crc32_le_combine(u32 crc1, u32 crc2, size_t len2) +EXPORT_SYMBOL(crc32_le); +EXPORT_SYMBOL(__crc32c_le); + +/* + * This multiplies the polynomials x and y modulo the given modulus. + * This follows the "little-endian" CRC convention that the lsbit + * represents the highest power of x, and the msbit represents x^0. + */ +static u32 __attribute_const__ gf2_multiply(u32 x, u32 y, u32 modulus) { - return crc32_generic_combine(crc1, crc2, len2, CRCPOLY_LE); + u32 product = x & 1 ? y : 0; + int i; + + for (i = 0; i < 31; i++) { + product = (product >> 1) ^ (product & 1 ? modulus : 0); + x >>= 1; + product ^= x & 1 ? y : 0; + } + + return product; } -u32 __pure __crc32c_le_combine(u32 crc1, u32 crc2, size_t len2) +/** + * crc32_generic_shift - Append len 0 bytes to crc, in logarithmic time + * @crc: The original little-endian CRC (i.e. lsbit is x^31 coefficient) + * @len: The number of bytes. @crc is multiplied by x^(8*@len) + * @polynomial: The modulus used to reduce the result to 32 bits. + * + * It's possible to parallelize CRC computations by computing a CRC + * over separate ranges of a buffer, then summing them. + * This shifts the given CRC by 8*len bits (i.e. produces the same effect + * as appending len bytes of zero to the data), in time proportional + * to log(len). + */ +static u32 __attribute_const__ crc32_generic_shift(u32 crc, size_t len, + u32 polynomial) { - return crc32_generic_combine(crc1, crc2, len2, CRC32C_POLY_LE); + u32 power = polynomial; /* CRC of x^32 */ + int i; + + /* Shift up to 32 bits in the simple linear way */ + for (i = 0; i < 8 * (int)(len & 3); i++) + crc = (crc >> 1) ^ (crc & 1 ? polynomial : 0); + + len >>= 2; + if (!len) + return crc; + + for (;;) { + /* "power" is x^(2^i), modulo the polynomial */ + if (len & 1) + crc = gf2_multiply(crc, power, polynomial); + + len >>= 1; + if (!len) + break; + + /* Square power, advancing to x^(2^(i+1)) */ + power = gf2_multiply(power, power, polynomial); + } + + return crc; } -EXPORT_SYMBOL(crc32_le); -EXPORT_SYMBOL(crc32_le_combine); -EXPORT_SYMBOL(__crc32c_le); -EXPORT_SYMBOL(__crc32c_le_combine); + +u32 __attribute_const__ crc32_le_shift(u32 crc, size_t len) +{ + return crc32_generic_shift(crc, len, CRCPOLY_LE); +} + +u32 __attribute_const__ __crc32c_le_shift(u32 crc, size_t len) +{ + return crc32_generic_shift(crc, len, CRC32C_POLY_LE); +} +EXPORT_SYMBOL(crc32_le_shift); +EXPORT_SYMBOL(__crc32c_le_shift); /** * crc32_be_generic() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32 |
