*** empty log message ***

[yaffs2.git] / yaffs_ecc.c

diff --git a/yaffs_ecc.c b/yaffs_ecc.c
index 5cb49b416d90933513592aff8dfa8b6802bb9446..59f3ed9cd118cffb98371b827605f282ac79b40a 100644 (file)
--- 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 1.6 2005-08-11 02:51:49 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 +283,21 @@ 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;
 
@@ -301,18 +310,20 @@ int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes,
 
                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;
 
 }
+