core/fs/btrfs/crc32c.h

   1 /*
   2  * Copied from Linux kernel crypto/crc32c.c
   3  * Copyright (c) 2004 Cisco Systems, Inc.
   4  * Copyright (c) 2008 Herbert Xu <herbert@gondor.apana.org.au>
   5  *
   6  * This program is free software; you can redistribute it and/or modify it
   7  * under the terms of the GNU General Public License as published by the Free
   8  * Software Foundation; either version 2 of the License, or (at your option)
   9  * any later version.
  10  *
  11  */
  12
  13 /*
  14  * This is the CRC-32C table
  15  * Generated with:
  16  * width = 32 bits
  17  * poly = 0x1EDC6F41
  18  * reflect input bytes = true
  19  * reflect output bytes = true
  20  */
  21
  22 static u32 crc32c_table[256];
  23
  24 /*
  25  * Steps through buffer one byte at at time, calculates reflected
  26  * crc using table.
  27  */
  28
  29 static inline u32 crc32c_le(u32 crc, const char *data, size_t length)
  30 {
  31         while (length--)
  32                 crc = crc32c_table[(u8)(crc ^ *data++)] ^ (crc >> 8);
  33
  34         return crc;
  35 }
  36
  37 static inline void btrfs_init_crc32c(void)
  38 {
  39         int i, j;
  40         u32 v;
  41         const u32 poly = 0x82F63B78; /* Bit-reflected CRC32C polynomial */
  42
  43         for (i = 0; i < 256; i++) {
  44                 v = i;
  45                 for (j = 0; j < 8; j++) {
  46                         v = (v >> 1) ^ ((v & 1) ? poly : 0);
  47                 }
  48                 crc32c_table[i] = v;
  49         }
  50 }