M17: CRC16 code cleanup

modemm17/CRC16.h

@@ -9,23 +9,28 @@
 namespace modemm17
 {
 
-template <uint16_t Poly = 0x5935, uint16_t Init = 0xFFFF>
 struct CRC16
 {
-    static constexpr uint16_t MASK = 0xFFFF;
-    static constexpr uint16_t LSB = 0x0001;
-    static constexpr uint16_t MSB = 0x8000;
+    static const uint16_t MASK = 0xFFFF;
+    static const uint16_t LSB = 0x0001;
+    static const uint16_t MSB = 0x8000;
 
-    uint16_t reg_ = Init;
+
+    CRC16(uint16_t poly = 0x5935, uint16_t init = 0xFFFF) :
+        poly_(poly),
+        init_(init)
+    {
+        reg_ = init_;
+    }
 
     void reset()
     {
-        reg_ = Init;
+        reg_ = init_;
 
         for (size_t i = 0; i != 16; ++i)
         {
             auto bit = reg_ & LSB;
-            if (bit) reg_ ^= Poly;
+            if (bit) reg_ ^= poly_;
             reg_ >>= 1;
             if (bit) reg_ |= MSB;
         }
@@ -44,7 +49,7 @@ struct CRC16
         {
             auto msb = reg & MSB;
             reg = ((reg << 1) & MASK) | ((byte >> (7 - i)) & LSB);
-            if (msb) reg ^= Poly;
+            if (msb) reg ^= poly_;
         }
         return reg & MASK;
     }
@@ -56,7 +61,7 @@ struct CRC16
         {
             auto msb = reg & MSB;
             reg = ((reg << 1) & MASK);
-            if (msb) reg ^= Poly;
+            if (msb) reg ^= poly_;
         }
         return reg;
     }
@@ -67,6 +72,11 @@ struct CRC16
         std::array<uint8_t, 2> result{uint8_t((crc >> 8) & 0xFF), uint8_t(crc & 0xFF)};
         return result;
     }
+
+private:
+    uint16_t poly_;
+    uint16_t init_;
+    uint16_t reg_;
 };
 
 } // modemm17

modemm17/M17FrameDecoder.h

@@ -45,7 +45,7 @@ struct M17FrameDecoder
     PolynomialInterleaver<45, 92, 368> interleaver_;
     Trellis<4,2> trellis_{makeTrellis<4, 2>({031,027})};
     Viterbi<decltype(trellis_), 4> viterbi_{trellis_};
-    CRC16<0x5935, 0xFFFF> crc_;
+    CRC16 crc_;
 
     enum class State { LSF, STREAM, BASIC_PACKET, FULL_PACKET, BERT };
     enum class SyncWordType { LSF, STREAM, PACKET, BERT };
@@ -106,6 +106,7 @@ struct M17FrameDecoder
     uint8_t lich_segments{0};       ///< one bit per received LICH fragment.
 
     M17FrameDecoder(callback_t callback) :
+        crc_(0x5935, 0xFFFF),
         callback_(callback)
     {}
 

modemm17/M17Modulator.h

@@ -51,7 +51,7 @@ public:
     static const std::array<uint8_t, 2> BERT_SYNC_WORD;
     static const std::array<uint8_t, 2> EOT_SYNC;
 
-    static constexpr int8_t bits_to_symbol(uint8_t bits)
+    static int8_t bits_to_symbol(uint8_t bits)
     {
         switch (bits)
         {
@@ -120,7 +120,7 @@ public:
 
         M17Randomizer<368> randomizer;
         PolynomialInterleaver<45, 92, 368> interleaver;
-        CRC16<0x5935, 0xFFFF> crc;
+        CRC16 crc(0x5935, 0xFFFF);
 
         auto rit = std::copy(dest_.begin(), dest_.end(), lsf.begin());
         std::copy(source_.begin(), source_.end(), rit);
@@ -457,7 +457,8 @@ public:
         source_(encode_callsign(source)),
         dest_(encode_callsign(dest)),
         can_(10),
-        rrc(makeFirFilter(rrc_taps))
+        rrc(makeFirFilter(rrc_taps)),
+        crc_(0x5935, 0xFFFF)
     {
         gnss_.fill(0);
         gnss_on_ = false;
@@ -511,7 +512,7 @@ private:
     uint8_t can_;
     BaseFirFilter<150> rrc;
     static const std::array<float, 150> rrc_taps;
-    CRC16<0x5935, 0xFFFF> crc_;
+    CRC16 crc_;
 
     static LinkSetupFrame::encoded_call_t encode_callsign(std::string callsign)
     {

plugins/channelrx/demodm17/m17demodprocessor.cpp

@@ -321,7 +321,7 @@ bool M17DemodProcessor::decode_packet(modemm17::M17FrameDecoder::packet_buffer_t
             qDebug() << "M17DemodProcessor::decode_packet: last chunk size:" << packet_size << " packet size:" << m_currentPacket.size();
         }
 
-        modemm17::CRC16<0x5935, 0xFFFF> crc16;
+        modemm17::CRC16 crc16(0x5935, 0xFFFF);
         crc16.reset();
 
         for (std::vector<uint8_t>::const_iterator it = m_currentPacket.begin(); it != m_currentPacket.end() - 2; ++it) {