From 8e3c84d97b15b18494da81ffdd2979d12d449ef8 Mon Sep 17 00:00:00 2001
From: Marek Sebera <marek.sebera@gmail.com>
Date: Sat, 30 Nov 2024 22:31:19 +0100
Subject: [PATCH] odd parity option for B.2.2.2 Reverse Channel Single Burst
 BPTC, fixes #9

---
 okdmr/dmrlib/etsi/fec/vbptc_32_11.py          |  8 ++++----
 .../tests/dmrlib/etsi/fec/test_vbptc_32_11.py | 20 +++++++++++--------
 2 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/okdmr/dmrlib/etsi/fec/vbptc_32_11.py b/okdmr/dmrlib/etsi/fec/vbptc_32_11.py
index 5444535..fefa29d 100644
--- a/okdmr/dmrlib/etsi/fec/vbptc_32_11.py
+++ b/okdmr/dmrlib/etsi/fec/vbptc_32_11.py
@@ -174,7 +174,7 @@ def fill_encoding_table(
         return table
 
     @staticmethod
-    def encode(bits_deinterleaved: bitarray) -> bitarray:
+    def encode(bits_deinterleaved: bitarray, even_parity: bool = True) -> bitarray:
         """
         Takes 11 bits of data (info bits) and return interleaved and FEC protected 32 bits
         :param bits_deinterleaved:
@@ -209,7 +209,7 @@ def encode(bits_deinterleaved: bitarray) -> bitarray:
 
         # fill columns with parity bit
         for column in range(0, 16):
-            table[:, column] = VBPTC3211.set_parity(table[:, column])
+            table[:, column] = VBPTC3211.set_parity(table[:, column], even_parity)
 
         out: bitarray = bitarray([0] * 32)
         for index, (
@@ -224,7 +224,7 @@ def encode(bits_deinterleaved: bitarray) -> bitarray:
         return out
 
     @staticmethod
-    def set_parity(column: numpy.ndarray) -> numpy.ndarray:
+    def set_parity(column: numpy.ndarray, even_parity: bool = True) -> numpy.ndarray:
         assert len(column) == 2
-        column[1] = column[0]
+        column[1] = column[0] if even_parity else not column[0]
         return column
diff --git a/okdmr/tests/dmrlib/etsi/fec/test_vbptc_32_11.py b/okdmr/tests/dmrlib/etsi/fec/test_vbptc_32_11.py
index 0b4cf6b..6d0e390 100644
--- a/okdmr/tests/dmrlib/etsi/fec/test_vbptc_32_11.py
+++ b/okdmr/tests/dmrlib/etsi/fec/test_vbptc_32_11.py
@@ -13,14 +13,18 @@ def test_vbptc_sanity():
 
 
 def test_encode_decode_vbptc():
-    bursts: List[(str,)] = [
-        ("00000100010110000000100010100100",),
+    # payload, even_parity
+    bursts: List[(str, bool)] = [
+        # even parity (default)
+        ("00000100010110000000100010100100", True),
+        # same payload mock with odd paritiy
+        ("01010001000011010101110111110001", False),
         # following are not valid vbptc protected payloads, probably something proprietary / unidentified
-        # ("00001100000100010010010001000001",),
-        # ("00010111000010100000011001000100",),
+        # ("00001100000100010010010001000001", ),
+        # ("00010111000010100000011001000100", ),
     ]
 
-    for (burst,) in bursts:
+    for burst, even_parity in bursts:
         on_air_bits = bitarray(burst)
 
         deinterleaved_all_bits = VBPTC3211.deinterleave_all_bits(on_air_bits)
@@ -31,9 +35,9 @@ def test_encode_decode_vbptc():
 
         deinterleaved_data_bits = VBPTC3211.deinterleave_data_bits(on_air_bits)
 
-        encoded_all_bits = VBPTC3211.encode(deinterleaved_all_bits)
-        encoded_data_bits = VBPTC3211.encode(deinterleaved_data_bits)
-        encoded_info_bits = VBPTC3211.encode(deinterleaved_info_bits)
+        encoded_all_bits = VBPTC3211.encode(deinterleaved_all_bits, even_parity)
+        encoded_data_bits = VBPTC3211.encode(deinterleaved_data_bits, even_parity)
+        encoded_info_bits = VBPTC3211.encode(deinterleaved_info_bits, even_parity)
 
         assert encoded_all_bits == encoded_data_bits
         assert encoded_data_bits == encoded_info_bits