From e63c0f9f88ce4cd02106811c663d50ee05e04d95 Mon Sep 17 00:00:00 2001
From: Andy <juribeparada@gmail.com>
Date: Fri, 26 Jan 2018 17:07:15 -0300
Subject: [PATCH] Fix Viterbi decoder for punctured codes

---
 NXDNConvolution.cpp | 17 +++++++++++++----
 NXDNSACCH.cpp       | 10 +++++-----
 2 files changed, 18 insertions(+), 9 deletions(-)
 mode change 100644 => 100755 NXDNConvolution.cpp
 mode change 100644 => 100755 NXDNSACCH.cpp

diff --git a/NXDNConvolution.cpp b/NXDNConvolution.cpp
old mode 100644
new mode 100755
index 83f73a0..2881412
--- a/NXDNConvolution.cpp
+++ b/NXDNConvolution.cpp
@@ -27,12 +27,12 @@ const unsigned char BIT_MASK_TABLE[] = {0x80U, 0x40U, 0x20U, 0x10U, 0x08U, 0x04U
 #define WRITE_BIT1(p,i,b) p[(i)>>3] = (b) ? (p[(i)>>3] | BIT_MASK_TABLE[(i)&7]) : (p[(i)>>3] & ~BIT_MASK_TABLE[(i)&7])
 #define READ_BIT1(p,i)    (p[(i)>>3] & BIT_MASK_TABLE[(i)&7])
 
-const uint8_t BRANCH_TABLE1[] = {0U, 0U, 0U, 0U, 2U, 2U, 2U, 2U};
-const uint8_t BRANCH_TABLE2[] = {0U, 2U, 2U, 0U, 0U, 2U, 2U, 0U};
+const uint8_t BRANCH_TABLE1[] = {0U, 0U, 0U, 0U, 1U, 1U, 1U, 1U};
+const uint8_t BRANCH_TABLE2[] = {0U, 1U, 1U, 0U, 0U, 1U, 1U, 0U};
 
 const unsigned int NUM_OF_STATES_D2 = 8U;
 const unsigned int NUM_OF_STATES = 16U;
-const uint32_t     M = 4U;
+const uint32_t     M = 2U;
 const unsigned int K = 5U;
 
 CNXDNConvolution::CNXDNConvolution() :
@@ -72,7 +72,16 @@ void CNXDNConvolution::decode(uint8_t s0, uint8_t s1)
   for (uint8_t i = 0U; i < NUM_OF_STATES_D2; i++) {
     uint8_t j = i * 2U;
 
-    uint16_t metric = (BRANCH_TABLE1[i] ^ s0) + (BRANCH_TABLE2[i] ^ s1);
+    uint16_t metric0 = 0;
+    uint16_t metric1 = 0;
+    
+	if (s0 != 99U)
+    	metric0 = (BRANCH_TABLE1[i] ^ s0);
+    	
+	if (s1 != 99U)
+    	metric1 = (BRANCH_TABLE2[i] ^ s1);
+    	
+    uint16_t metric = metric0 + metric1;
 
     uint16_t m0 = m_oldMetrics[i] + metric;
     uint16_t m1 = m_oldMetrics[i + NUM_OF_STATES_D2] + (M - metric);
diff --git a/NXDNSACCH.cpp b/NXDNSACCH.cpp
old mode 100644
new mode 100755
index b6b26cb..262cde2
--- a/NXDNSACCH.cpp
+++ b/NXDNSACCH.cpp
@@ -86,14 +86,14 @@ bool CNXDNSACCH::decode(const unsigned char* data)
 	unsigned int index = 0U;
 	for (unsigned int i = 0U; i < NXDN_SACCH_LENGTH_BITS; i++) {
 		if (n == PUNCTURE_LIST[index]) {
-			::strcat(text, "1, ");
-			temp2[n++] = 1U;
+			::strcat(text, "X, ");
+			temp2[n++] = 99U;
 			index++;
 		}
 
 		bool b = READ_BIT1(temp1, i);
-		temp2[n++] = b ? 2U : 0U;
-		::strcat(text, b ? "2, " : "0, ");
+		temp2[n++] = b ? 1U : 0U;
+		::strcat(text, b ? "1, " : "0, ");
 	}
 
 	LogMessage(text);
@@ -109,7 +109,7 @@ bool CNXDNSACCH::decode(const unsigned char* data)
 		conv.decode(s0, s1);
 	}
 
-	conv.chainback(m_data, 36U);
+	conv.chainback(m_data, 32U);
 
 	CUtils::dump("NXDN, SACCH decoded", m_data, 5U);