lib/crc.c

/* crc.c -- cyclic redundancy checks
   Copyright (C) 2005-2006, 2009-2026 Free Software Foundation, Inc.

   This file is free software: you can redistribute it and/or modify
   it under the terms of the GNU Lesser General Public License as
   published by the Free Software Foundation, either version 3 of the
   License, or (at your option) any later version.

   This file is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

/* Written by Simon Josefsson.  */

#include <config.h>

#include "crc.h"
#include "endian.h"

#ifdef GL_CRC_X86_64_PCLMUL
#include "cpu-supports.h"
#include "crc-x86_64.h"
static bool pclmul_enabled = false;
static bool pclmul_checked = false;
#endif

#include <string.h>

#if GL_CRC_SLICE_BY_8
# include "crc-sliceby8.h"

/*
 * When we calculate the CRC32 byte-by-byte we take the checksum
 * up to the previous byte, XOR it with our new byte, run CRC32
 * and then XOR against the remaining bytes from the prior checksum:
 *
 * c0 = prior checksum
 * d0,d1 = bytes 0 and 1 of our data
 * c1 = (c0 >> 8)
 * c2 = CRC32(c0 ^ d0) ^ c1
 * c3 = (c2 >> 8)
 * c4 = CRC32(c2 ^ d1) ^ c3
 *
 * The CRC32 function is "affine" which means that
 * CRC32(a ^ b) = CRC32(a) ^ CRC32(b)
 *
 * and therefore we can move some of the terms around, e.g.
 *
 * c4 = CRC32(CRC32(c0 ^ d0) ^ c1 ^ d1) ^ c3
 * c4 = CRC32(CRC32(c0 ^ d0)) ^ CRC32(c1 ^ d1) ^ c3
 *
 * Another way to look at this is
 *
 * CRC32(0x1200) ^ CRC32(0x34) = CRC32(0x1234)
 *
 * With the slice-by-8 method, we extend the table-lookup technique
 * from a single table of 0x00 to 0xFF, but also every 0x100 from
 * 0x0000 to 0xFF00, and for 0x000000 to 0xFF0000 etc.
 *
 * We can then calculate by taking 8 bytes of plaintext and then
 * looking up each one individually and XORing them together
 * at the end.
 *
 * This approach has been mentioned by multiple sources but one of
 * the common references is 10.1109/TC.2008.85 by Kounavis
 * and Berry
 */

static uint32_t
crc32_update_no_xor_slice_by_8 (uint32_t crc, const char *buf)
{
  uint64_t local_buf;
  memcpy (&local_buf, buf, 8);
  local_buf = le64toh (local_buf) ^ crc;

  uint32_t final_crc = crc32_sliceby8_table[0][(local_buf >> 56) & 0xFF]
                       ^ crc32_sliceby8_table[1][(local_buf >> 48) & 0xFF]
                       ^ crc32_sliceby8_table[2][(local_buf >> 40) & 0xFF]
                       ^ crc32_sliceby8_table[3][(local_buf >> 32) & 0xFF]
                       ^ crc32_sliceby8_table[4][(local_buf >> 24) & 0xFF]
                       ^ crc32_sliceby8_table[5][(local_buf >> 16) & 0xFF]
                       ^ crc32_sliceby8_table[6][(local_buf >> 8) & 0xFF]
                       ^ crc32_sliceby8_table[7][local_buf & 0xFF];

  return final_crc;
}

static uint32_t
crc32_update_no_xor_slice_by_n (uint32_t crc, const char *buf,
                                size_t num_bytes)
{
  uint64_t local_buf;
  memcpy (&local_buf, buf, num_bytes);
  local_buf = le64toh (local_buf) ^ crc;

  if (num_bytes >= 4)
    crc = 0;
  else
    crc = crc >> (num_bytes * 8);

  for (size_t i = 0; i < num_bytes; i++)
    {
      size_t shift_amount = ((num_bytes - i - 1) * 8);
      crc = crc ^ crc32_sliceby8_table[i][(local_buf >> shift_amount) & 0xFF];
    }

  return crc;
}

uint32_t
crc32_update_no_xor (uint32_t crc, const char *buf, size_t len)
{
# ifdef GL_CRC_X86_64_PCLMUL
  if (!pclmul_checked)
    {
      pclmul_enabled = (cpu_supports ("pclmul")
                        && cpu_supports ("avx"));
      pclmul_checked = true;
    }

  if (pclmul_enabled && len >= 16)
    return crc32_update_no_xor_pclmul (crc, buf, len);
# endif

  size_t slice_alignment = (len & (-8));

  size_t n;
  for (n = 0; n < slice_alignment; n += 8)
    crc = crc32_update_no_xor_slice_by_8 (crc, buf + n);

  if (len > n)
    crc = crc32_update_no_xor_slice_by_n (crc, buf + n, len - n);

  return crc;
}

#else

/* Table of CRCs of all 8-bit messages.  Generated by running code
   from RFC 1952 modified to print out the table. */
static const uint32_t crc32_table[256] = {
  0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f,
  0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
  0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2,
  0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
  0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
  0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
  0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa, 0x42b2986c,
  0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
  0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423,
  0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
  0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 0x01db7106,
  0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
  0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d,
  0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
  0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
  0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
  0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7,
  0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
  0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa,
  0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
  0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81,
  0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
  0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84,
  0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
  0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
  0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
  0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8, 0xa1d1937e,
  0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
  0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55,
  0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
  0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28,
  0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
  0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f,
  0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
  0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
  0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
  0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69,
  0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
  0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc,
  0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
  0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693,
  0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
  0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
};

/*
 * The following function was extracted from RFC 1952 by Simon
 * Josefsson.  It was modified to avoid initial and final XOR, to use
 * size_t for the buffer length, and to use the const keyword.
 */
uint32_t
crc32_update_no_xor (uint32_t crc, const char *buf, size_t len)
{
# ifdef GL_CRC_X86_64_PCLMUL
  if (!pclmul_checked)
    {
      pclmul_enabled = (cpu_supports ("pclmul")
                        && cpu_supports ("avx"));
      pclmul_checked = true;
    }

  if (pclmul_enabled && len >= 16)
    return crc32_update_no_xor_pclmul (crc, buf, len);
# endif

  for (size_t n = 0; n < len; n++)
    crc = crc32_table[(crc ^ buf[n]) & 0xff] ^ (crc >> 8);

  return crc;
}

#endif

uint32_t
crc32_no_xor (const char *buf, size_t len)
{
  return crc32_update_no_xor (0L, buf, len);
}

uint32_t
crc32_update (uint32_t crc, const char *buf, size_t len)
{
  return crc32_update_no_xor (crc ^ 0xffffffff, buf, len) ^ 0xffffffff;
}

uint32_t
crc32 (const char *buf, size_t len)
{
  return crc32_update (0L, buf, len);
}