/*
* 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 appropriate multiple
* of the divisor to subtract to being the remainder back into range.
* In binary, it's easy - it has to be either 0 or 1, and to make the
* XOR cancel, it's just a copy of bit 32 of the remainder.
*
* When computing a CRC, we don't care about the quotient, so we can
* throw the quotient bit away, but subtract the appropriate multiple of
* the polynomial from the remainder and we're back to where we started,
* ready to process the next bit.
*
* A big-endian CRC written this way would be coded like:
* for (i = 0; i < input_bits; i++) {
* multiple = remainder & 0x80000000 ? CRCPOLY : 0;
* remainder = (remainder << 1 | next_input_bit()) ^ multiple;
* }
* Notice how, to get at bit 32 of the shifted remainder, we look
* at bit 31 of the remainder *before* shifting it.
*
* But also notice how the next_input_bit() bits we're shifting into
* the remainder don't actually affect any decision-making until
* 32 bits later. Thus, the first 32 cycles of this are pretty boring.
* Also, to add the CRC to a message, we need a 32-bit-long hole for it at
* the end, so we have to add 32 extra cycles shifting in zeros at the
* end of every message,
*
* So the standard trick is to rearrage merging in the next_input_bit()
* until the moment it's needed. Then the first 32 cycles can be precomputed,
* and merging in the final 32 zero bits to make room for the CRC can be
* skipped entirely.
* This changes the code to:
* for (i = 0; i < input_bits; i++) {
* remainder ^= next_input_bit() << 31;
* multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
* remainder = (remainder << 1) ^ multiple;
* }
* With this optimization, the little-endian code is simpler:
* for (i = 0; i < input_bits; i++) {
* remainder ^= next_input_bit();
* multiple = (remainder & 1) ? CRCPOLY : 0;
* remainder = (remainder >> 1) ^ multiple;
* }
*
* Note that the other details of endianness have been hidden in CRCPOLY
* (which must be bit-reversed) and next_input_bit().
*
* However, as long as next_input_bit is returning the bits in a sensible
* order, we can actually do the merging 8 or more bits at a time rather
* than one bit at a time:
* for (i = 0; i < input_bytes; i++) {
* remainder ^= next_input_byte() << 24;
* for (j = 0; j < 8; j++) {
* multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
* remainder = (remainder << 1) ^ multiple;
* }
* }
* Or in little-endian:
* for (i = 0; i < input_bytes; i++) {
* remainder ^= next_input_byte();
* for (j = 0; j < 8; j++) {
* multiple = (remainder & 1) ? CRCPOLY : 0;
* remainder = (remainder << 1) ^ multiple;
* }
* }
* If the input is a multiple of 32 bits, you can even XOR in a 32-bit
* word at a time and increase the inner loop count to 32.
*
* You can also mix and match the two loop styles, for example doing the
* bulk of a message byte-at-a-time and adding bit-at-a-time processing
* for any fractional bytes at the end.
*
* The only remaining optimization is to the byte-at-a-time table method.
* Here, rather than just shifting one bit of the remainder to decide
* in the correct multiple to subtract, we can shift a byte at a time.
* This produces a 40-bit (rather than a 33-bit) intermediate remainder,
* but again the multiple of the polynomial to subtract depends only on
* the high bits, the high 8 bits in this case.
*
* The multiple we need in that case is the low 32 bits of a 40-bit
* value whose high 8 bits are given, and which is a multiple of the
* generator polynomial. This is simply the CRC-32 of the given
* one-byte message.
*
* Two more details: normally, appending zero bits to a message which
* is already a multiple of a polynomial produces a larger multiple of that
* polynomial. To enable a CRC to detect this condition, it's common to
* invert the CRC before appending it. This makes the remainder of the
* message+crc come out not as zero, but some fixed non-zero value.
*
* The same problem applies to zero bits prepended to the message, and
* a similar solution is used. Instead of starting with a remainder of
* 0, an initial remainder of all ones is used. As long as you start
* the same way on decoding, it doesn't make a difference.
*/
#ifdef UNITTEST
#include <stdlib.h>
#include <stdio.h>
const __u8 byte_rev_table[256] = {
0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0,
0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8,
0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8,
0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4,
0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec,
0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc,
0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2,
0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2,
0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea,
0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6,
0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6,
0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee,
0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe,
0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1,
0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9,
0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9,
0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5,
0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5,
0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed,
0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3,
0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3,
0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb,
0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb,
0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7,
0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef,
0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff,
};
static inline __u8 bitrev8(__u8 byte)
{
return byte_rev_table[byte];
}
static inline __u16 bitrev16(__u16 x)
{
return (bitrev8(x & 0xff) << 8) | bitrev8(x >> 8);
}
/**
* bitrev32 - reverse the order of bits in a u32 value
* @x: value to be bit-reversed
*/
static __u32 bitrev32(__u32 x)
{
return (bitrev16(x & 0xffff) << 16) | bitrev16(x >> 16);
}
#if 0 /*Not used at present */
static void
buf_dump(char const *prefix, unsigned char const *buf, size_t len)
{
fputs(prefix, stdout);
while (len--)
printf(" %02x", *buf++);
putchar('\n');
}
#endif
static void bytereverse(unsigned char *buf, size_t len)
{
while (len--) {
unsigned char x = bitrev8(*buf);
*buf++ = x;
}
}
static void random_garbage(unsigned char *buf, size_t len)
{
while (len--)
*buf++ = (unsigned char) random();
}
#if 0 /* Not used at present */
static void store_le(__u32 x, unsigned char *buf)
{
buf[0] = (unsigned char) x;
buf[1] = (unsigned char) (x >> 8);
buf[2] = (unsigned char) (x >> 16);
buf[3] = (unsigned char) (x >> 24);
}
#endif
static void store_be(__u32 x, unsigned char *buf)
{
buf[0] = (unsigned char) (x >> 24);
buf[1] = (unsigned char) (x >> 16);
buf[2] = (unsigned char) (x >> 8);
buf[3] = (unsigned char) x;
}
/*
* This checks that CRC(buf + CRC(buf)) = 0, and that
* CRC commutes with bit-reversal. This has the side effect
* of bytewise bit-reversing the input buffer, and returns
* the CRC of the reversed buffer.
*/
static __u32 test_step(__u32 init, unsigned char *buf, size_t len)
{
__u32 crc1, crc2;
size_t i;
crc1 = crc32_be(init, buf, len);
store_be(crc1, buf + len);
crc2 = crc32_be(init, buf, len + 4);
if (crc2)
printf("\nCRC cancellation fail: 0x%08x should be 0\n",
crc2);
for (i = 0; i <= len + 4; i++) {
crc2 = crc32_be(init, buf, i);
crc2 = crc32_be(crc2, buf + i, len + 4 - i);
if (crc2)
printf("\nCRC split fail: 0x%08x\n", crc2);
}
/* Now swap it around for the other test */
bytereverse(buf, len + 4);
init = bitrev32(init);
crc2 = bitrev32(crc1);
if (crc1 != bitrev32(crc2))
printf("\nBit reversal fail: 0x%08x -> 0x%08x -> 0x%08x\n",
crc1, crc2, bitrev32(crc2));
crc1 = crc32_le(init, buf, len);
if (crc1 != crc2)
printf("\nCRC endianness fail: 0x%08x != 0x%08x\n", crc1,
crc2);
crc2 = crc32_le(init, buf, len + 4);
if (crc2)
printf("\nCRC cancellation fail: 0x%08x should be 0\n",
crc2);
for (i = 0; i <= len + 4; i++) {
crc2 = crc32_le(init, buf, i);
crc2 = crc32_le(crc2, buf + i, len + 4 - i);
if (crc2)
printf("\nCRC split fail: 0x%08x\n", crc2);
}
return crc1;
}
#define SIZE 64
#define INIT1 0
#define INIT2 0
int main(int argc, char **argv)
{
unsigned char buf1[SIZE + 4];
unsigned char buf2[SIZE + 4];
unsigned char buf3[SIZE + 4];
int i, j;
__u32 crc1, crc2, crc3;
int exit_status = 0;
for (i = 0; i <= SIZE; i++) {
printf("\rTesting length %d...", i);
fflush(stdout);
random_garbage(buf1, i);
random_garbage(buf2, i);
for (j = 0; j < i; j++)
buf3[j] = buf1[j] ^ buf2[j];
crc1 = test_step(INIT1, buf1, i);
crc2 = test_step(INIT2, buf2, i);
/* Now check that CRC(buf1 ^ buf2) = CRC(buf1) ^ CRC(buf2) */
crc3 = test_step(INIT1 ^ INIT2, buf3, i);
if (crc3 != (crc1 ^ crc2)) {
printf("CRC XOR fail: 0x%08x != 0x%08x ^ 0x%08x\n",
crc3, crc1, crc2);
exit_status++;
}
}
printf("\nAll test complete. No failures expected.\n");
return 0;
}
#endif /* UNITTEST */