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/*

 * 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 <linux/crc32.h>

#include <linux/kernel.h>

#include <linux/module.h>

#include <linux/config.h>

#include <linux/types.h>

#include <linux/slab.h>

#include <linux/init.h>

#include <asm/atomic.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"

#if __GNUC__ >= 3       /* 2.x has "attribute", but only 3.0 has "pure */

#define attribute(x) __attribute__(x)

#else

#define attribute(x)

#endif

MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");

MODULE_DESCRIPTION("Ethernet CRC32 calculations");

MODULE_LICENSE("GPL");

#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.

 */

/**

 * 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 attribute((pure)) 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 */

/**

 * 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 attribute((pure)) 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 __LITTLE_ENDIAN

#  define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8)

# else

#  define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8)

# endif

        crc = __cpu_to_le32(crc);

        /* Align it */

        if(unlikely(((long)b)&3 && len)){

                do {

                        DO_CRC(*((u8 *)b)++);

                } 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 {

                        DO_CRC(*((u8 *)b)++);

                } 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

#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.

 */

/**

 * 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 attribute((pure)) 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 */

/**

 * 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 attribute((pure)) crc32_be(u32 crc, unsigned char const *p, size_t len)

{

# if CRC_BE_BITS == 8

        const u32      *b =(u32 *)p;

        const u32      *tab = crc32table_be;

# ifdef __LITTLE_ENDIAN

#  define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8)

# else

#  define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8)

# endif

        crc = __cpu_to_be32(crc);

        /* Align it */

        if(unlikely(((long)b)&3 && len)){

                do {

                        DO_CRC(*((u8 *)b)++);

                } 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 {

                        DO_CRC(*((u8 *)b)++);

                } 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

u32 bitreverse(u32 x)

{

        x = (x >> 16) | (x << 16);

        x = (x >> 8 & 0x00ff00ff) | (x << 8 & 0xff00ff00);

        x = (x >> 4 & 0x0f0f0f0f) | (x << 4 & 0xf0f0f0f0);

        x = (x >> 2 & 0x33333333) | (x << 2 & 0xcccccccc);

        x = (x >> 1 & 0x55555555) | (x << 1 & 0xaaaaaaaa);

        return x;

}

#ifndef CONFIG_CRC32 

        /* To ensure that this file is pulled in from lib/lib.a if it's

           configured in but nothing in-kernel uses it, we export its

           symbols from kernel/ksyms.c in the CONFIG_CRC32=y case.

           Otherwise (either modular or pulled in by the makefile magic)

           we export them from here. */

EXPORT_SYMBOL(crc32_le);

EXPORT_SYMBOL(crc32_be);

EXPORT_SYMBOL(bitreverse);

#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 multile 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.

 */

#if UNITTEST

#include <stdlib.h>

#include <stdio.h>

#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 = *buf;

                x = (x >> 4) | (x << 4);

                x = (x >> 2 & 0x33) | (x << 2 & 0xcc);

                x = (x >> 1 & 0x55) | (x << 1 & 0xaa);

                *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 = bitreverse(init);

        crc2 = bitreverse(crc1);

        if (crc1 != bitreverse(crc2))

                printf("\nBit reversal fail: 0x%08x -> %0x08x -> 0x%08x\n",

                       crc1, crc2, bitreverse(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(void)

{

        unsigned char buf1[SIZE + 4];

        unsigned char buf2[SIZE + 4];

        unsigned char buf3[SIZE + 4];

        int i, j;

        u32 crc1, crc2, crc3;

        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);

        }

        printf("\nAll test complete.  No failures expected.\n");

        return 0;

}

#endif                          /* UNITTEST */