From 8d5d7fc0c2d20dcc2a85fee329141f271855638b Mon Sep 17 00:00:00 2001
From: Ahmet Inan <xdsopl@gmail.com>
Date: Wed, 21 Jul 2021 17:15:47 +0200
Subject: [PATCH] use the DVB recommended T=10 BCH code

---
 README.md |  4 ++--
 decode.cc | 12 ++++++------
 encode.cc |  8 ++++----
 3 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/README.md b/README.md
index d897e5e..cba0480 100644
--- a/README.md
+++ b/README.md
@@ -3,10 +3,10 @@
 
 Quick start:
 
-Create file ```uncoded.dat``` with ```43008``` bits of random data:
+Create file ```uncoded.dat``` with ```43040``` bits of random data:
 
 ```
-dd if=/dev/urandom of=uncoded.dat bs=1 count=5376
+dd if=/dev/urandom of=uncoded.dat bs=1 count=5380
 ```
 
 Encode file ```uncoded.dat``` to ```encoded.wav``` [WAV](https://en.wikipedia.org/wiki/WAV) audio file with 8000 Hz sample rate, 16 bits and only 1 (real) channel:
diff --git a/decode.cc b/decode.cc
index c1f5b74..33b9003 100644
--- a/decode.cc
+++ b/decode.cc
@@ -162,7 +162,7 @@ struct Decoder
 	static const int guard_len = symbol_len / 8;
 	static const int ldpc_bits = 64800;
 	static const int bch_bits = ldpc_bits - 21600;
-	static const int data_bits = bch_bits - 12 * 16;
+	static const int data_bits = bch_bits - 10 * 16;
 	static const int mod_min = 2;
 	static const int mod_max = 3;
 	static const int cons_max = ldpc_bits / mod_min;
@@ -187,12 +187,12 @@ struct Decoder
 	CODE::CRC<uint16_t> crc0;
 	typedef CODE::GaloisField<16, 0b10000000000101101, uint16_t> GF;
 	GF gf;
-	CODE::BoseChaudhuriHocquenghemDecoder<24, 1, 65343, GF> bchdec1;
+	CODE::BoseChaudhuriHocquenghemDecoder<20, 1, 65375, GF> bchdec1;
 	CODE::OrderedStatisticsDecoder<255, 71, 4> osddec;
 	CODE::LDPCDecoder<DVB_T2_TABLE_A3, 1> ldpcdec;
 	int8_t genmat[255*71];
 	int8_t code[ldpc_bits], bint[ldpc_bits];
-	uint16_t erasures[24];
+	uint16_t erasures[20];
 	cmplx head[symbol_len], tail[symbol_len], cons[cons_max];
 	cmplx fdom[symbol_len], tdom[buffer_len], resam[buffer_len];
 	value cfo_rad, sfo_rad;
@@ -478,10 +478,10 @@ struct Decoder
 		int ecnt = 0;
 		for (int i = 0; i < bch_bits; ++i) {
 			if (!code[i]) {
-				if (ecnt < 24) {
+				if (ecnt < 20) {
 					erasures[ecnt++] = i;
 				} else {
-					std::cerr << "payload LDPC produced more than 24 erasures." << std::endl;
+					std::cerr << "payload LDPC produced more than 20 erasures." << std::endl;
 					return;
 				}
 			}
@@ -548,7 +548,7 @@ int main(int argc, char **argv)
 		std::cerr << "Couldn't open file \"" << output_name << "\" for writing." << std::endl;
 		return 1;
 	}
-	const int data_len = code_len - (12 * 16 + 21600) / 8;
+	const int data_len = code_len - (10 * 16 + 21600) / 8;
 	CODE::Xorshift32 scrambler;
 	for (int i = 0; i < data_len; ++i)
 		output_data[i] ^= scrambler();
diff --git a/encode.cc b/encode.cc
index f4efcfb..439befc 100644
--- a/encode.cc
+++ b/encode.cc
@@ -30,7 +30,7 @@ struct Encoder
 	static const int guard_len = symbol_len / 8;
 	static const int ldpc_bits = 64800;
 	static const int bch_bits = ldpc_bits - 21600;
-	static const int data_bits = bch_bits - 12 * 16;
+	static const int data_bits = bch_bits - 10 * 16;
 	static const int mls0_len = 127;
 	static const int mls0_poly = 0b10001001;
 	static const int mls1_len = 255;
@@ -42,7 +42,7 @@ struct Encoder
 	DSP::FastFourierTransform<4*symbol_len, cmplx, 1> bwd4;
 	CODE::CRC<uint16_t> crc0;
 	CODE::BoseChaudhuriHocquenghemEncoder<255, 71> bchenc0;
-	CODE::BoseChaudhuriHocquenghemEncoder<65535, 65343> bchenc1;
+	CODE::BoseChaudhuriHocquenghemEncoder<65535, 65375> bchenc1;
 	CODE::LDPCEncoder<DVB_T2_TABLE_A3> ldpcenc;
 	int8_t code[ldpc_bits], bint[ldpc_bits];
 	cmplx fdom[symbol_len], fdom4[4*symbol_len];
@@ -199,7 +199,7 @@ struct Encoder
 			0b10000000000101101, 0b10000000101110011, 0b10000111110111101,
 			0b10101101001010101, 0b10001111100101111, 0b11111011110110101,
 			0b11010111101100101, 0b10111001101100111, 0b10000111010100001,
-			0b10111010110100111, 0b10011101000101101, 0b10001101011100011}),
+			0b10111010110100111}),
 			oper_mode(oper_mode)
 	{
 		switch (oper_mode) {
@@ -337,7 +337,7 @@ int main(int argc, char **argv)
 		return 1;
 	}
 	const int code_len = 64800 / 8;
-	const int data_len = code_len - (12 * 16 + 21600) / 8;
+	const int data_len = code_len - (10 * 16 + 21600) / 8;
 	uint8_t *input_data = new uint8_t[code_len];
 	for (int i = 0; i < data_len; ++i)
 		input_data[i] = input_file.get();