X-Git-Url: http://www.aleph1.co.uk/gitweb/?p=yaffs2.git;a=blobdiff_plain;f=yaffs_ecc.c;h=813ce6d48f8543e2db7e25b9b56d9c0430a8ae7c;hp=5cb49b416d90933513592aff8dfa8b6802bb9446;hb=20488750f4e5df4cec34f2bd4db39ab7e075d0a9;hpb=68f0159122cfb94e6912dd99d6398ba72e578a72

diff --git a/yaffs_ecc.c b/yaffs_ecc.c
index 5cb49b4..813ce6d 100644
--- a/yaffs_ecc.c
+++ b/yaffs_ecc.c
@@ -23,14 +23,15 @@
   *
   */
 
-// 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.
+/* 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 $";
+    "$Id: yaffs_ecc.c,v 1.7 2006-09-14 22:02:46 charles Exp $";
 
 #include "yportenv.h"
 
@@ -71,6 +72,8 @@ static const unsigned char column_parity_table[] = {
 	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;
@@ -93,6 +96,7 @@ static int yaffs_CountBits32(unsigned x)
 	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;
@@ -163,24 +167,25 @@ void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc)
 #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 
+	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;
@@ -222,25 +227,31 @@ 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 ((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;
+		return 1; /* Corrected the error */
 	}
-	// Unrecoverable 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)
 {
@@ -255,8 +266,8 @@ void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes,
 		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;
 		}
@@ -272,23 +283,22 @@ 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 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) {
-		// no error
-		return 0;
-	}
+	if ((cDelta | lDelta | lDeltaPrime) == 0)
+		return 0; /* no error */
 
-	if (lDelta == ~lDeltaPrime && (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15))	// Not correct 
+	if (lDelta == ~lDeltaPrime && 
+	    (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15))
 	{
-		// Single bit (recoverable) error in data
+		/* Single bit (recoverable) error in data */
 
 		bit = 0;
 
@@ -299,20 +309,25 @@ int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes,
 		if (cDelta & 0x02)
 			bit |= 0x01;
 
+		if(lDelta >= nBytes)
+			return -1;
+			
 		data[lDelta] ^= (1 << bit);
 
-		return 1;
+		return 1; /* corrected */
 	}
 
 	if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) +
 	     yaffs_CountBits(cDelta)) == 1) {
-		// Reccoverable error in ecc
+		/* Reccoverable error in ecc */
 
 		*read_ecc = *test_ecc;
-		return 1;
+		return 1; /* corrected */
 	}
-	// Unrecoverable error
+
+	/* Unrecoverable error */
 
 	return -1;
 
 }
+