drivers/mtd/ubi/crc32.c - github/trini/u-boot - Gitiles

 /*
  * 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.
  */

 #ifdef UBI_LINUX
 #include <linux/crc32.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/compiler.h>
 #endif
 #include <linux/types.h>

 #include <asm/byteorder.h>

 #ifdef UBI_LINUX
 #include <linux/slab.h>
 #include <linux/init.h>
 #include <asm/atomic.h>
 #endif
 #include "crc32defs.h"
 #define CRC_LE_BITS 8

 # define __force
 #ifndef __constant_cpu_to_le32
 #define __constant_cpu_to_le32(x) ((__force __le32)(__u32)(x))
 #endif
 #ifndef __constant_le32_to_cpu
 #define __constant_le32_to_cpu(x) ((__force __u32)(__le32)(x))
 #endif

 #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 UBI_LINUX
 MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
 MODULE_DESCRIPTION("Ethernet CRC32 calculations");
 MODULE_LICENSE("GPL");
 #endif
 /**
  * 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 __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
     //printf("Crc32_le crc=%x\n",crc);
 	crc = __cpu_to_le32(crc);
 	/* Align it */
 	if((((long)b)&3 && len)){
 		do {
 			u8 *p = (u8 *)b;
 			DO_CRC(*p++);
 			b = (void *)p;
 		} while ((--len) && ((long)b)&3 );
 	}
 	if((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
 #ifdef UBI_LINUX
 /**
  * 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 == 1
 /*
  * In fact, the table-based code will work in this case, but it can be
  * simplified by inlining the table in ?: form.
  */

 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 */
 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 {
 			u8 *p = (u8 *)b;
 			DO_CRC(*p++);
 			b = (u32 *)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 __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

 EXPORT_SYMBOL(crc32_le);
 EXPORT_SYMBOL(crc32_be);
 #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.
  */

 #ifdef UNITTEST

 #include <stdlib.h>
 #include <stdio.h>

 #ifdef UBI_LINUX				/*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();
 }

 #ifdef UBI_LINUX				/* 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(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 */
	/*
	* 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.
	*/

	#ifdef UBI_LINUX
	#include <linux/crc32.h>
	#include <linux/kernel.h>
	#include <linux/module.h>
	#include <linux/compiler.h>
	#endif
	#include <linux/types.h>

	#include <asm/byteorder.h>

	#ifdef UBI_LINUX
	#include <linux/slab.h>
	#include <linux/init.h>
	#include <asm/atomic.h>
	#endif
	#include "crc32defs.h"
	#define CRC_LE_BITS 8

	# define __force
	#ifndef __constant_cpu_to_le32
	#define __constant_cpu_to_le32(x) ((__force __le32)(__u32)(x))
	#endif
	#ifndef __constant_le32_to_cpu
	#define __constant_le32_to_cpu(x) ((__force __u32)(__le32)(x))
	#endif

	#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 UBI_LINUX
	MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
	MODULE_DESCRIPTION("Ethernet CRC32 calculations");
	MODULE_LICENSE("GPL");
	#endif
	/**
	* 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 __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
	//printf("Crc32_le crc=%x\n",crc);
	crc = __cpu_to_le32(crc);
	/* Align it */
	if((((long)b)&3 && len)){
	do {
	u8 p = (u8 )b;
	DO_CRC(*p++);
	b = (void *)p;
	} while ((--len) && ((long)b)&3 );
	}
	if((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
	#ifdef UBI_LINUX
	/**
	* 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 == 1
	/*
	* In fact, the table-based code will work in this case, but it can be
	* simplified by inlining the table in ?: form.
	*/

	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 */
	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 {
	u8 p = (u8 )b;
	DO_CRC(*p++);
	b = (u32 *)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 __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

	EXPORT_SYMBOL(crc32_le);
	EXPORT_SYMBOL(crc32_be);
	#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.
	*/

	#ifdef UNITTEST

	#include <stdlib.h>
	#include <stdio.h>

	#ifdef UBI_LINUX /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();
	}

	#ifdef UBI_LINUX /* 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(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 */