/*
* crc32.c --- CRC32 function
*
* Copyright (C) 2008 Theodore Ts'o.
*
* %Begin-Header%
* This file may be redistributed under the terms of the GNU Public
* License.
* %End-Header%
*/
/*
* Oct 15, 2000 Matt Domsch <Matt_Domsch@dell.com>
* Nicer crc32 functions/docs submitted by linux@horizon.com. Thanks!
* Code was from the public domain, copyright abandoned. Code was
* subsequently included in the kernel, thus was re-licensed under the
* GNU GPL v2.
*
* Oct 12, 2000 Matt Domsch <Matt_Domsch@dell.com>
* Same crc32 function was used in 5 other places in the kernel.
* I made one version, and deleted the others.
* There are various incantations of crc32(). Some use a seed of 0 or ~0.
* Some xor at the end with ~0. The generic crc32() function takes
* seed as an argument, and doesn't xor at the end. Then individual
* users can do whatever they need.
* drivers/net/smc9194.c uses seed ~0, doesn't xor with ~0.
* fs/jffs2 uses seed 0, doesn't xor with ~0.
* fs/partitions/efi.c uses seed ~0, xor's with ~0.
*
* This source code is licensed under the GNU General Public License,
* Version 2. See the file COPYING for more details.
*/
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#ifdef UNITTEST
#undef ENABLE_NLS
#endif
#include "e2fsck.h"
#include "crc32defs.h"
#if CRC_LE_BITS == 8
#define tole(x) __constant_cpu_to_le32(x)
#define tobe(x) __constant_cpu_to_be32(x)
#else
#define tole(x) (x)
#define tobe(x) (x)
#endif
#include "crc32table.h"
#ifdef UNITTEST
/**
* crc32_le() - Calculate bitwise little-endian Ethernet AUTODIN II CRC32
* @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for
* other uses, or the previous crc32 value if computing incrementally.
* @p: pointer to buffer over which CRC is run
* @len: length of buffer @p
*/
__u32 crc32_le(__u32 crc, unsigned char const *p, size_t len);
#if CRC_LE_BITS == 1
/*
* In fact, the table-based code will work in this case, but it can be
* simplified by inlining the table in ?: form.
*/
__u32 crc32_le(__u32 crc, unsigned char const *p, size_t len)
{
int i;
while (len--) {
crc ^= *p++;
for (i = 0; i < 8; i++)
crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0);
}
return crc;
}
#else /* Table-based approach */
__u32 crc32_le(__u32 crc, unsigned char const *p, size_t len)
{
# if CRC_LE_BITS == 8
const __u32 *b =(__u32 *)p;
const __u32 *tab = crc32table_le;
# ifdef WORDS_BIGENDIAN
# define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8)
# else
# define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8)
# endif
crc = __cpu_to_le32(crc);
/* Align it */
if(unlikely(((long)b)&3 && len)){
do {
__u8 *p = (__u8 *)b;
DO_CRC(*p++);
b = (void *)p;
} while ((--len) && ((long)b)&3 );
}
if(likely(len >= 4)){
/* load data 32 bits wide, xor data 32 bits wide. */
size_t save_len = len & 3;
len = len >> 2;
--b; /* use pre increment below(*++b) for speed */
do {
crc ^= *++b;
DO_CRC(0);
DO_CRC(0);
DO_CRC(0);
DO_CRC(0);
} while (--len);
b++; /* point to next byte(s) */
len = save_len;
}
/* And the last few bytes */
if(len){
do {
__u8 *p = (__u8 *)b;
DO_CRC(*p++);
b = (void *)p;
} while (--len);
}
return __le32_to_cpu(crc);
#undef ENDIAN_SHIFT
#undef DO_CRC
# elif CRC_LE_BITS == 4
while (len--) {
crc ^= *p++;
crc = (crc >> 4) ^ crc32table_le[crc & 15];
crc = (crc >> 4) ^ crc32table_le[crc & 15];
}
return crc;
# elif CRC_LE_BITS == 2
while (len--) {
crc ^= *p++;
crc = (crc >> 2) ^ crc32table_le[crc & 3];
crc = (crc >> 2) ^ crc32table_le[crc & 3];
crc = (crc >> 2) ^ crc32table_le[crc & 3];
crc = (crc >> 2) ^ crc32table_le[crc & 3];
}
return crc;
# endif
}
#endif
#endif /* UNITTEST */
/**
* crc32_be() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
* @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for
* other uses, or the previous crc32 value if computing incrementally.
* @p: pointer to buffer over which CRC is run
* @len: length of buffer @p
*/
__u32 crc32_be(__u32 crc, unsigned char const *p, size_t len);
#if CRC_BE_BITS == 1
/*
* In fact, the table-based code will work in this case, but it can be
* simplified by inlining the table in ?: form.
*/
__u32 crc32_be(__u32 crc, unsigned char const *p, size_t len)
{
int i;
while (len--) {
crc ^= *p++ << 24;
for (i = 0; i < 8; i++)
crc =
(crc << 1) ^ ((crc & 0x80000000) ? CRCPOLY_BE :
0);
}
return crc;
}
#else /* Table-based approach */
__u32 crc32_be(__u32 crc, unsigned char const *p, size_t len)
{
# if CRC_BE_BITS == 8
const __u32 *b =(const __u32 *)p;
const __u32 *tab = crc32table_be;
# ifdef WORDS_BIGENDIAN
# define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8)
# else
# define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8)
# endif
crc = __cpu_to_be32(crc);
/* Align it */
if(unlikely(((long)b)&3 && len)){
do {
const __u8 *q = (const __u8 *)b;
DO_CRC(*q++);
b = (const __u32 *)q;
} while ((--len) && ((long)b)&3 );
}
if(likely(len >= 4)){
/* load data 32 bits wide, xor data 32 bits wide. */
size_t save_len = len & 3;
len = len >> 2;
--b; /* use pre increment below(*++b) for speed */
do {
crc ^= *++b;
DO_CRC(0);
DO_CRC(0);
DO_CRC(0);
DO_CRC(0);
} while (--len);
b++; /* point to next byte(s) */
len = save_len;
}
/* And the last few bytes */
if(len){
do {
const __u8 *q = (const __u8 *)b;
DO_CRC(*q++);
b = (const void *)q;
} while (--len);
}
return __be32_to_cpu(crc);
#undef ENDIAN_SHIFT
#undef DO_CRC
# elif CRC_BE_BITS == 4
while (len--) {
crc ^= *p++ << 24;
crc = (crc << 4) ^ crc32table_be[crc >> 28];
crc = (crc << 4) ^ crc32table_be[crc >> 28];
}
return crc;
# elif CRC_BE_BITS == 2
while (len--) {
crc ^= *p++ << 24;
crc = (crc << 2) ^ crc32table_be[crc >> 30];
crc = (crc << 2) ^ crc32table_be[crc >> 30];
crc = (crc << 2) ^ crc32table_be[crc >> 30];
crc = (crc << 2) ^ crc32table_be[crc >> 30];
}
return crc;
# endif
}
#endif
/*
* A brief CRC tutorial.
*
* A CRC is a long-division remainder. You add the CRC to the message,
* and the whole thing (message+CRC) is a multiple of the given
* CRC polynomial. To check the CRC, you can either check that the
* CRC matches the recomputed value, *or* you can check that the
* remainder computed on the message+CRC is 0. This latter approach
* is used by a lot of hardware implementations, and is why so many
* protocols put the end-of-frame flag after the CRC.
*
* It's actually the same long division you learned in school, except that
* - We're working in binary, so the digits are only 0 and 1, and
* - When dividing polynomials, there are no carries. Rather than add and
* subtract, we just xor. Thus, we tend to get a bit sloppy about
* the difference between adding and subtracting.
*
* A 32-bit CRC polynomial is actually 33 bits long. But since it's
* 33 bits long, bit 32 is always going to be set, so usually the CRC
* is written in hex with the most significant bit omitted. (If you're
* familiar with the IEEE 754 floating-point format, it's the same idea.)
*
* Note that a CRC is computed over a string of *bits*, so you have
* to decide on the endianness of the bits within each byte. To get
* the best error-detecting properties, this should correspond to the
* order they're actually sent. For example, standard RS-232 serial is
* little-endian; the most significant bit (sometimes used for parity)
* is sent last. And when appending a CRC word to a message, you should
* do it in the right order, matching the endianness.
*
* Just like with ordinary division, the remainder is always smaller than
* the divisor (the CRC polynomial) you're dividing by. Each step of the
* division, you take one more digit (bit) of the dividend and append it
* to the current remainder. Then you figure out the app
