yaffs2/yaffs_ecc.c - platform/external/yaffs2 - Git at Google

 /*
  * YAFFS: Yet another FFS. A NAND-flash specific file system.
  *
  * yaffs_ecc.c: ECC generation/correction algorithms.
  *
  * Copyright (C) 2002 Aleph One Ltd.
  *
  * Created by Charles Manning <charles@aleph1.co.uk>
  *
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
  * version 2.1 as published by the Free Software Foundation.
  */

  /*
   * This code implements the ECC algorithm used in SmartMedia.
   *
   * The ECC comprises 22 bits of parity information and is stuffed into 3 bytes.
   * The two unused bit are set to 1.
   * The ECC can correct single bit errors in a 256-byte page of data. Thus, two such ECC
   * blocks are used on a 512-byte NAND page.
   *
   */

 /* Table generated by gen-ecc.c
  * Using a table means we do not have to calculate p1..p4 and p1'..p4'
  * for each byte of data. These are instead provided in a table in bits7..2.
  * Bit 0 of each entry indicates whether the entry has an odd or even parity, and therefore
  * this bytes influence on the line parity.
  */

 const char *yaffs_ecc_c_version =
     "$Id: yaffs_ecc.c,v 1.7 2006/09/14 22:02:46 charles Exp $";

 #include "yportenv.h"

 #include "yaffs_ecc.h"

 static const unsigned char column_parity_table[] = {
 	0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
 	0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
 	0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
 	0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
 	0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
 	0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
 	0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
 	0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
 	0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
 	0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
 	0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
 	0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
 	0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
 	0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
 	0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
 	0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
 	0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
 	0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
 	0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
 	0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
 	0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
 	0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
 	0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
 	0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
 	0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
 	0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
 	0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
 	0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
 	0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
 	0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
 	0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
 	0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
 };

 /* Count the bits in an unsigned char or a U32 */

 static int yaffs_CountBits(unsigned char x)
 {
 	int r = 0;
 	while (x) {
 		if (x & 1)
 			r++;
 		x >>= 1;
 	}
 	return r;
 }

 static int yaffs_CountBits32(unsigned x)
 {
 	int r = 0;
 	while (x) {
 		if (x & 1)
 			r++;
 		x >>= 1;
 	}
 	return r;
 }

 /* Calculate the ECC for a 256-byte block of data */
 void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc)
 {
 	unsigned int i;

 	unsigned char col_parity = 0;
 	unsigned char line_parity = 0;
 	unsigned char line_parity_prime = 0;
 	unsigned char t;
 	unsigned char b;

 	for (i = 0; i < 256; i++) {
 		b = column_parity_table[*data++];
 		col_parity ^= b;

 		if (b & 0x01)	// odd number of bits in the byte
 		{
 			line_parity ^= i;
 			line_parity_prime ^= ~i;
 		}

 	}

 	ecc[2] = (~col_parity) | 0x03;

 	t = 0;
 	if (line_parity & 0x80)
 		t |= 0x80;
 	if (line_parity_prime & 0x80)
 		t |= 0x40;
 	if (line_parity & 0x40)
 		t |= 0x20;
 	if (line_parity_prime & 0x40)
 		t |= 0x10;
 	if (line_parity & 0x20)
 		t |= 0x08;
 	if (line_parity_prime & 0x20)
 		t |= 0x04;
 	if (line_parity & 0x10)
 		t |= 0x02;
 	if (line_parity_prime & 0x10)
 		t |= 0x01;
 	ecc[1] = ~t;

 	t = 0;
 	if (line_parity & 0x08)
 		t |= 0x80;
 	if (line_parity_prime & 0x08)
 		t |= 0x40;
 	if (line_parity & 0x04)
 		t |= 0x20;
 	if (line_parity_prime & 0x04)
 		t |= 0x10;
 	if (line_parity & 0x02)
 		t |= 0x08;
 	if (line_parity_prime & 0x02)
 		t |= 0x04;
 	if (line_parity & 0x01)
 		t |= 0x02;
 	if (line_parity_prime & 0x01)
 		t |= 0x01;
 	ecc[0] = ~t;

 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
 	// Swap the bytes into the wrong order
 	t = ecc[0];
 	ecc[0] = ecc[1];
 	ecc[1] = t;
 #endif
 }


 /* Correct the ECC on a 256 byte block of data */

 int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc,
 		     const unsigned char *test_ecc)
 {
 	unsigned char d0, d1, d2;	/* deltas */

 	d0 = read_ecc[0] ^ test_ecc[0];
 	d1 = read_ecc[1] ^ test_ecc[1];
 	d2 = read_ecc[2] ^ test_ecc[2];

 	if ((d0 | d1 | d2) == 0)
 		return 0; /* no error */

 	if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 &&
 	    ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 &&
 	    ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) {
 		/* Single bit (recoverable) error in data */

 		unsigned byte;
 		unsigned bit;

 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
 		// swap the bytes to correct for the wrong order
 		unsigned char t;

 		t = d0;
 		d0 = d1;
 		d1 = t;
 #endif

 		bit = byte = 0;

 		if (d1 & 0x80)
 			byte |= 0x80;
 		if (d1 & 0x20)
 			byte |= 0x40;
 		if (d1 & 0x08)
 			byte |= 0x20;
 		if (d1 & 0x02)
 			byte |= 0x10;
 		if (d0 & 0x80)
 			byte |= 0x08;
 		if (d0 & 0x20)
 			byte |= 0x04;
 		if (d0 & 0x08)
 			byte |= 0x02;
 		if (d0 & 0x02)
 			byte |= 0x01;

 		if (d2 & 0x80)
 			bit |= 0x04;
 		if (d2 & 0x20)
 			bit |= 0x02;
 		if (d2 & 0x08)
 			bit |= 0x01;

 		data[byte] ^= (1 << bit);

 		return 1; /* Corrected the error */
 	}

 	if ((yaffs_CountBits(d0) +
 	     yaffs_CountBits(d1) +
 	     yaffs_CountBits(d2)) ==  1) {
 		/* Reccoverable error in ecc */

 		read_ecc[0] = test_ecc[0];
 		read_ecc[1] = test_ecc[1];
 		read_ecc[2] = test_ecc[2];

 		return 1; /* Corrected the error */
 	}

 	/* Unrecoverable error */

 	return -1;

 }


 /*
  * ECCxxxOther does ECC calcs on arbitrary n bytes of data
  */
 void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes,
 			     yaffs_ECCOther * eccOther)
 {
 	unsigned int i;

 	unsigned char col_parity = 0;
 	unsigned line_parity = 0;
 	unsigned line_parity_prime = 0;
 	unsigned char b;

 	for (i = 0; i < nBytes; i++) {
 		b = column_parity_table[*data++];
 		col_parity ^= b;

 		if (b & 0x01)	 {
 			/* odd number of bits in the byte */
 			line_parity ^= i;
 			line_parity_prime ^= ~i;
 		}

 	}

 	eccOther->colParity = (col_parity >> 2) & 0x3f;
 	eccOther->lineParity = line_parity;
 	eccOther->lineParityPrime = line_parity_prime;
 }

 int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes,
 			  yaffs_ECCOther * read_ecc,
 			  const yaffs_ECCOther * test_ecc)
 {
 	unsigned char cDelta;	/* column parity delta */
 	unsigned lDelta;	/* line parity delta */
 	unsigned lDeltaPrime;	/* line parity delta */
 	unsigned bit;

 	cDelta = read_ecc->colParity ^ test_ecc->colParity;
 	lDelta = read_ecc->lineParity ^ test_ecc->lineParity;
 	lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime;

 	if ((cDelta | lDelta | lDeltaPrime) == 0)
 		return 0; /* no error */

 	if (lDelta == ~lDeltaPrime &&
 	    (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15))
 	{
 		/* Single bit (recoverable) error in data */

 		bit = 0;

 		if (cDelta & 0x20)
 			bit |= 0x04;
 		if (cDelta & 0x08)
 			bit |= 0x02;
 		if (cDelta & 0x02)
 			bit |= 0x01;

 		if(lDelta >= nBytes)
 			return -1;

 		data[lDelta] ^= (1 << bit);

 		return 1; /* corrected */
 	}

 	if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) +
 	     yaffs_CountBits(cDelta)) == 1) {
 		/* Reccoverable error in ecc */

 		*read_ecc = *test_ecc;
 		return 1; /* corrected */
 	}

 	/* Unrecoverable error */

 	return -1;

 }
	/*
	* YAFFS: Yet another FFS. A NAND-flash specific file system.
	*
	* yaffs_ecc.c: ECC generation/correction algorithms.
	*
	* Copyright (C) 2002 Aleph One Ltd.
	*
	* Created by Charles Manning <charles@aleph1.co.uk>
	*
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU Lesser General Public License
	* version 2.1 as published by the Free Software Foundation.
	*/

	/*
	* This code implements the ECC algorithm used in SmartMedia.
	*
	* The ECC comprises 22 bits of parity information and is stuffed into 3 bytes.
	* The two unused bit are set to 1.
	* The ECC can correct single bit errors in a 256-byte page of data. Thus, two such ECC
	* blocks are used on a 512-byte NAND page.
	*
	*/

	/* Table generated by gen-ecc.c
	* Using a table means we do not have to calculate p1..p4 and p1'..p4'
	* for each byte of data. These are instead provided in a table in bits7..2.
	* Bit 0 of each entry indicates whether the entry has an odd or even parity, and therefore
	* this bytes influence on the line parity.
	*/

	const char *yaffs_ecc_c_version =
	"$Id: yaffs_ecc.c,v 1.7 2006/09/14 22:02:46 charles Exp $";

	#include "yportenv.h"

	#include "yaffs_ecc.h"

	static const unsigned char column_parity_table[] = {
	0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
	0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
	0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
	0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
	0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
	0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
	0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
	0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
	0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
	0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
	0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
	0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
	0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
	0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
	0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
	0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
	0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
	0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
	0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
	0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
	0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
	0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
	0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
	0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
	0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
	0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
	0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
	0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
	0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
	0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
	0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
	0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
	};

	/* Count the bits in an unsigned char or a U32 */

	static int yaffs_CountBits(unsigned char x)
	{
	int r = 0;
	while (x) {
	if (x & 1)
	r++;
	x >>= 1;
	}
	return r;
	}

	static int yaffs_CountBits32(unsigned x)
	{
	int r = 0;
	while (x) {
	if (x & 1)
	r++;
	x >>= 1;
	}
	return r;
	}

	/* Calculate the ECC for a 256-byte block of data */
	void yaffs_ECCCalculate(const unsigned char data, unsigned char ecc)
	{
	unsigned int i;

	unsigned char col_parity = 0;
	unsigned char line_parity = 0;
	unsigned char line_parity_prime = 0;
	unsigned char t;
	unsigned char b;

	for (i = 0; i < 256; i++) {
	b = column_parity_table[*data++];
	col_parity ^= b;

	if (b & 0x01) // odd number of bits in the byte
	{
	line_parity ^= i;
	line_parity_prime ^= ~i;
	}

	}

	ecc[2] = (~col_parity) \| 0x03;

	t = 0;
	if (line_parity & 0x80)
	t \|= 0x80;
	if (line_parity_prime & 0x80)
	t \|= 0x40;
	if (line_parity & 0x40)
	t \|= 0x20;
	if (line_parity_prime & 0x40)
	t \|= 0x10;
	if (line_parity & 0x20)
	t \|= 0x08;
	if (line_parity_prime & 0x20)
	t \|= 0x04;
	if (line_parity & 0x10)
	t \|= 0x02;
	if (line_parity_prime & 0x10)
	t \|= 0x01;
	ecc[1] = ~t;

	t = 0;
	if (line_parity & 0x08)
	t \|= 0x80;
	if (line_parity_prime & 0x08)
	t \|= 0x40;
	if (line_parity & 0x04)
	t \|= 0x20;
	if (line_parity_prime & 0x04)
	t \|= 0x10;
	if (line_parity & 0x02)
	t \|= 0x08;
	if (line_parity_prime & 0x02)
	t \|= 0x04;
	if (line_parity & 0x01)
	t \|= 0x02;
	if (line_parity_prime & 0x01)
	t \|= 0x01;
	ecc[0] = ~t;

	#ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
	// Swap the bytes into the wrong order
	t = ecc[0];
	ecc[0] = ecc[1];
	ecc[1] = t;
	#endif
	}


	/* Correct the ECC on a 256 byte block of data */

	int yaffs_ECCCorrect(unsigned char data, unsigned char read_ecc,
	const unsigned char *test_ecc)
	{
	unsigned char d0, d1, d2; /* deltas */

	d0 = read_ecc[0] ^ test_ecc[0];
	d1 = read_ecc[1] ^ test_ecc[1];
	d2 = read_ecc[2] ^ test_ecc[2];

	if ((d0 \| d1 \| d2) == 0)
	return 0; /* no error */

	if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 &&
	((d1 ^ (d1 >> 1)) & 0x55) == 0x55 &&
	((d2 ^ (d2 >> 1)) & 0x54) == 0x54) {
	/* Single bit (recoverable) error in data */

	unsigned byte;
	unsigned bit;

	#ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
	// swap the bytes to correct for the wrong order
	unsigned char t;

	t = d0;
	d0 = d1;
	d1 = t;
	#endif

	bit = byte = 0;

	if (d1 & 0x80)
	byte \|= 0x80;
	if (d1 & 0x20)
	byte \|= 0x40;
	if (d1 & 0x08)
	byte \|= 0x20;
	if (d1 & 0x02)
	byte \|= 0x10;
	if (d0 & 0x80)
	byte \|= 0x08;
	if (d0 & 0x20)
	byte \|= 0x04;
	if (d0 & 0x08)
	byte \|= 0x02;
	if (d0 & 0x02)
	byte \|= 0x01;

	if (d2 & 0x80)
	bit \|= 0x04;
	if (d2 & 0x20)
	bit \|= 0x02;
	if (d2 & 0x08)
	bit \|= 0x01;

	data[byte] ^= (1 << bit);

	return 1; /* Corrected the error */
	}

	if ((yaffs_CountBits(d0) +
	yaffs_CountBits(d1) +
	yaffs_CountBits(d2)) == 1) {
	/* Reccoverable error in ecc */

	read_ecc[0] = test_ecc[0];
	read_ecc[1] = test_ecc[1];
	read_ecc[2] = test_ecc[2];

	return 1; /* Corrected the error */
	}

	/* Unrecoverable error */

	return -1;

	}


	/*
	* ECCxxxOther does ECC calcs on arbitrary n bytes of data
	*/
	void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes,
	yaffs_ECCOther * eccOther)
	{
	unsigned int i;

	unsigned char col_parity = 0;
	unsigned line_parity = 0;
	unsigned line_parity_prime = 0;
	unsigned char b;

	for (i = 0; i < nBytes; i++) {
	b = column_parity_table[*data++];
	col_parity ^= b;

	if (b & 0x01) {
	/* odd number of bits in the byte */
	line_parity ^= i;
	line_parity_prime ^= ~i;
	}

	}

	eccOther->colParity = (col_parity >> 2) & 0x3f;
	eccOther->lineParity = line_parity;
	eccOther->lineParityPrime = line_parity_prime;
	}

	int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes,
	yaffs_ECCOther * read_ecc,
	const yaffs_ECCOther * test_ecc)
	{
	unsigned char cDelta; /* column parity delta */
	unsigned lDelta; /* line parity delta */
	unsigned lDeltaPrime; /* line parity delta */
	unsigned bit;

	cDelta = read_ecc->colParity ^ test_ecc->colParity;
	lDelta = read_ecc->lineParity ^ test_ecc->lineParity;
	lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime;

	if ((cDelta \| lDelta \| lDeltaPrime) == 0)
	return 0; /* no error */

	if (lDelta == ~lDeltaPrime &&
	(((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15))
	{
	/* Single bit (recoverable) error in data */

	bit = 0;

	if (cDelta & 0x20)
	bit \|= 0x04;
	if (cDelta & 0x08)
	bit \|= 0x02;
	if (cDelta & 0x02)
	bit \|= 0x01;

	if(lDelta >= nBytes)
	return -1;

	data[lDelta] ^= (1 << bit);

	return 1; /* corrected */
	}

	if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) +
	yaffs_CountBits(cDelta)) == 1) {
	/* Reccoverable error in ecc */

	read_ecc = test_ecc;
	return 1; /* corrected */
	}

	/* Unrecoverable error */

	return -1;

	}