Merge pull request #61 from srcejon/fix_golay20

Fix Golay_20_8 parity correction

dmr.cpp

@@ -993,7 +993,7 @@ void DSDDMR::processSlotTypePDU()
 
         unsigned int dataType = (slotTypeBits[4] << 3) + (slotTypeBits[5] << 2) + (slotTypeBits[6] << 1) + slotTypeBits[7];
 
-        if (dataType > DMR_TYPES_COUNT)
+        if (dataType >= DMR_TYPES_COUNT)
         {
             m_dataType = DSDDMRDataReserved;
             memcpy(&m_slotText[4], "RES", 3);

fec.cpp

@@ -650,7 +650,7 @@ void Golay_20_8::init()
                 int syndromeIP = syndromeI ^ (1 << (11-ip));
                 m_corr[syndromeIP][0] = i1;
                 m_corr[syndromeIP][1] = i2;
-                m_corr[syndromeIP][2] = 12 + ip;
+                m_corr[syndromeIP][2] = 8 + ip;
             }
         }
 
@@ -669,14 +669,14 @@ void Golay_20_8::init()
         {
             int syndromeIP1 = syndromeI ^ (1 << (11-ip1));
             m_corr[syndromeIP1][0] = i1;
-            m_corr[syndromeIP1][1] = 12 + ip1;
+            m_corr[syndromeIP1][1] = 8 + ip1;
 
             for (int ip2 = ip1+1; ip2 < 12; ip2++) // 1 more bit flip in parity
             {
                 int syndromeIP2 = syndromeIP1 ^ (1 << (11-ip2));
                 m_corr[syndromeIP2][0] = i1;
-                m_corr[syndromeIP2][1] = 12 + ip1;
-                m_corr[syndromeIP2][2] = 12 + ip2;
+                m_corr[syndromeIP2][1] = 8 + ip1;
+                m_corr[syndromeIP2][2] = 8 + ip2;
             }
         }
     }
@@ -685,20 +685,20 @@ void Golay_20_8::init()
     for (int ip1 = 0; ip1 < 12; ip1++) // 1 bit flip in parity
     {
         int syndromeIP1 =  (1 << (11-ip1));
-        m_corr[syndromeIP1][0] = 12 + ip1;
+        m_corr[syndromeIP1][0] = 8 + ip1;
 
         for (int ip2 = ip1+1; ip2 < 12; ip2++) // 1 more bit flip in parity
         {
             int syndromeIP2 = syndromeIP1 ^ (1 << (11-ip2));
-            m_corr[syndromeIP2][0] = 12 + ip1;
-            m_corr[syndromeIP2][1] = 12 + ip2;
+            m_corr[syndromeIP2][0] = 8 + ip1;
+            m_corr[syndromeIP2][1] = 8 + ip2;
 
             for (int ip3 = ip2+1; ip3 < 12; ip3++) // 1 more bit flip in parity
             {
                 int syndromeIP3 = syndromeIP2 ^ (1 << (11-ip3));
-                m_corr[syndromeIP3][0] = 12 + ip1;
-                m_corr[syndromeIP3][1] = 12 + ip2;
-                m_corr[syndromeIP3][2] = 12 + ip3;
+                m_corr[syndromeIP3][0] = 8 + ip1;
+                m_corr[syndromeIP3][1] = 8 + ip2;
+                m_corr[syndromeIP3][2] = 8 + ip3;
             }
         }
     }

testfec/Makefile

@@ -28,7 +28,7 @@ hamming16: fec.o hamming16.cpp
 	g++ -o hamming16 fec.o hamming16.cpp
 
 golay20: fec.o golay20.cpp
-	g++ -o golay20 fec.o golay20.cpp
+	g++ $(CXXLFAGS) -o golay20 fec.o golay20.cpp
 
 golay23: fec.o golay23.cpp
 	g++ -o golay23 fec.o golay23.cpp
@@ -65,4 +65,3 @@ descramble.o: ../descramble.h ../descramble.cpp
 
 clean:
 	rm -f *.o qr golay20 golay23 golay24 hamming7 hamming12 hamming15 hamming16 viterbi viterbi35 crc
-

testfec/golay20.cpp

@@ -41,6 +41,87 @@ void decode(DSDcc::Golay_20_8& Golay_20_8, unsigned char *codeword)
     }
 }
 
+void rand_test()
+{
+    unsigned char msg[8];
+    unsigned char codeword[20], xcodeword[20];
+    int idx1, idx2, idx3;
+    int dataIn, dataOut;
+    int passCount = 0, failCount = 0, parityFailCount = 0;
+    DSDcc::Golay_20_8 golay_20_8;
+
+    // Run multiple times, to randomly corrupt different bits
+    // Takes about 10 seconds on a fast PC
+    for (int repeat = 0; repeat < 100000; repeat++)
+    {
+        // Exhaustively test all 8-bit inputs
+        for (int dataIn = 0; dataIn < 256; dataIn++)
+        {
+            // Convert to array of bits
+            for (int j = 0; j < 8; j++) {
+                msg[j] = (dataIn >> j) & 1;
+            }
+
+            // Encode
+            golay_20_8.encode(msg, codeword);
+
+            // Save copy of uncorrupted codeword
+            std::copy(codeword, codeword + 20, xcodeword);
+
+            // Randomly corrupt up to 3 bits
+            idx1 = rand() % 20;
+            idx2 = rand() % 20;
+            idx3 = rand() % 20;
+            codeword[idx1] ^= codeword[idx1];
+            codeword[idx2] ^= codeword[idx2];
+            codeword[idx3] ^= codeword[idx3];
+
+            bool fail = false;
+            // Decode and correct errors
+            dataOut = 0;
+            if (golay_20_8.decode(codeword))
+            {
+                // Check data is corrected
+                for (int j = 0; j < 8; j++) {
+                    dataOut |= codeword[j] << j;
+                }
+                if (dataIn != dataOut) {
+                    fail = true;
+                }
+
+                // Check also that parity has been corrected, as we previously had a bug with this
+                if (memcmp(codeword, xcodeword, 20)) {
+                    parityFailCount++;
+                }
+            }
+            else
+            {
+                fail = true;
+            }
+            if (fail)
+            {
+                std::cout << "Decode failed:"
+                    << " dataIn=" << dataIn
+                    << " dataOut=" << dataOut
+                    << " idx1=" << idx1
+                    << " idx2=" << idx2
+                    << " idx3=" << idx3
+                    << "\n";
+                failCount++;
+            }
+            else
+            {
+                passCount++;
+            }
+        }
+    }
+
+    std::cout << "rand_test:"
+        << " Passcount=" << passCount
+        << " Failcount=" << failCount
+        << " parityFailCount=" << parityFailCount << "\n";
+}
+
 int main(int argc, char *argv[])
 {
     unsigned char msg[8]  = {1, 0, 0, 1, 0, 1, 0, 0};
@@ -106,6 +187,8 @@ int main(int argc, char *argv[])
     xcodeword[19] ^= 1;
     decode(golay_20_8, xcodeword);
 
+    rand_test();
+
     return 0;
 }