X-Git-Url: http://www.aleph1.co.uk/gitweb/?p=yaffs2.git;a=blobdiff_plain;f=yaffs_ecc.c;h=9294107c150d261bbb6c90c8c78b6590ba4b97a4;hp=5cb49b416d90933513592aff8dfa8b6802bb9446;hb=0459b0b3f858ef3e840b93d723a3b2cad862d95f;hpb=68f0159122cfb94e6912dd99d6398ba72e578a72

diff --git a/yaffs_ecc.c b/yaffs_ecc.c
index 5cb49b4..9294107 100644
--- a/yaffs_ecc.c
+++ b/yaffs_ecc.c
@@ -1,41 +1,37 @@
 /*
- * YAFFS: Yet another FFS. A NAND-flash specific file system. 
+ * YAFFS: Yet Another Flash File System. A NAND-flash specific file system.
  *
- * yaffs_ecc.c: ECC generation/correction algorithms.
- *
- * Copyright (C) 2002 Aleph One Ltd.
+ * Copyright (C) 2002-2011 Aleph One Ltd.
+ *   for Toby Churchill Ltd and Brightstar Engineering
  *
  * 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 program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 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 1.5 2005-08-11 00:34:14 charles Exp $";
+/*
+ * 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.
+ *
+ */
 
 #include "yportenv.h"
 
 #include "yaffs_ecc.h"
 
+/* 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.
+ */
+
 static const unsigned char column_parity_table[] = {
 	0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
 	0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
@@ -71,32 +67,11 @@ static const unsigned char column_parity_table[] = {
 	0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
 };
 
-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;
-}
 
-void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc)
+/* Calculate the ECC for a 256-byte block of data */
+void yaffs_ecc_calc(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;
@@ -107,12 +82,10 @@ void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc)
 		b = column_parity_table[*data++];
 		col_parity ^= b;
 
-		if (b & 0x01)	// odd number of bits in the byte
-		{
+		if (b & 0x01) {	/* odd number of bits in the byte */
 			line_parity ^= i;
 			line_parity_prime ^= ~i;
 		}
-
 	}
 
 	ecc[2] = (~col_parity) | 0x03;
@@ -155,45 +128,30 @@ void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc)
 		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
 }
 
-int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc,
-		     const unsigned char *test_ecc)
+/* Correct the ECC on a 256 byte block of data */
+
+int yaffs_ecc_correct(unsigned char *data, unsigned char *read_ecc,
+		      const unsigned char *test_ecc)
 {
-	unsigned char d0, d1, d2;	// deltas 
+	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) {
-		// no error
-		return 0;
-	}
+	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
+		/* 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)
@@ -222,97 +180,102 @@ int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc,
 
 		data[byte] ^= (1 << bit);
 
-		return 1;
+		return 1;	/* Corrected the error */
 	}
 
-	if ((yaffs_CountBits(d0) + yaffs_CountBits(d1) + yaffs_CountBits(d2)) ==
-	    1) {
-		// Reccoverable error in ecc
+	if ((hweight8(d0) + hweight8(d1) + hweight8(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;
+		return 1;	/* Corrected the error */
 	}
-	// Unrecoverable error
+
+	/* Unrecoverable error */
 
 	return -1;
 
 }
 
-void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes,
-			     yaffs_ECCOther * eccOther)
+/*
+ * ECCxxxOther does ECC calcs on arbitrary n bytes of data
+ */
+void yaffs_ecc_calc_other(const unsigned char *data, unsigned n_bytes,
+			  struct yaffs_ecc_other *ecc_other)
 {
 	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++) {
+	for (i = 0; i < n_bytes; i++) {
 		b = column_parity_table[*data++];
 		col_parity ^= b;
 
-		if (b & 0x01)	// odd number of bits in the byte
-		{
+		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;
+	ecc_other->col_parity = (col_parity >> 2) & 0x3f;
+	ecc_other->line_parity = line_parity;
+	ecc_other->line_parity_prime = line_parity_prime;
 }
 
-int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes,
-			  yaffs_ECCOther * read_ecc,
-			  const yaffs_ECCOther * test_ecc)
+int yaffs_ecc_correct_other(unsigned char *data, unsigned n_bytes,
+			    struct yaffs_ecc_other *read_ecc,
+			    const struct yaffs_ecc_other *test_ecc)
 {
-	unsigned char cDelta;	// column parity delta
-	unsigned lDelta;	// line parity delta
-	unsigned lDeltaPrime;	// line parity delta
+	unsigned char delta_col;	/* column parity delta */
+	unsigned delta_line;	/* line parity delta */
+	unsigned delta_line_prime;	/* 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;
+	delta_col = read_ecc->col_parity ^ test_ecc->col_parity;
+	delta_line = read_ecc->line_parity ^ test_ecc->line_parity;
+	delta_line_prime =
+	    read_ecc->line_parity_prime ^ test_ecc->line_parity_prime;
 
-	if ((cDelta | lDelta | lDeltaPrime) == 0) {
-		// no error
-		return 0;
-	}
+	if ((delta_col | delta_line | delta_line_prime) == 0)
+		return 0;	/* no error */
 
-	if (lDelta == ~lDeltaPrime && (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15))	// Not correct 
-	{
-		// Single bit (recoverable) error in data
+	if (delta_line == ~delta_line_prime &&
+	    (((delta_col ^ (delta_col >> 1)) & 0x15) == 0x15)) {
+		/* Single bit (recoverable) error in data */
 
 		bit = 0;
 
-		if (cDelta & 0x20)
+		if (delta_col & 0x20)
 			bit |= 0x04;
-		if (cDelta & 0x08)
+		if (delta_col & 0x08)
 			bit |= 0x02;
-		if (cDelta & 0x02)
+		if (delta_col & 0x02)
 			bit |= 0x01;
 
-		data[lDelta] ^= (1 << bit);
+		if (delta_line >= n_bytes)
+			return -1;
 
-		return 1;
+		data[delta_line] ^= (1 << bit);
+
+		return 1;	/* corrected */
 	}
 
-	if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) +
-	     yaffs_CountBits(cDelta)) == 1) {
-		// Reccoverable error in ecc
+	if ((hweight32(delta_line) +
+	     hweight32(delta_line_prime) +
+	     hweight8(delta_col)) == 1) {
+		/* Reccoverable error in ecc */
 
 		*read_ecc = *test_ecc;
-		return 1;
+		return 1;	/* corrected */
 	}
-	// Unrecoverable error
 
-	return -1;
+	/* Unrecoverable error */
 
+	return -1;
 }