From f8b782033d0b07a78f380e37f55cef808ff5857b Mon Sep 17 00:00:00 2001
From: Ahmet Inan <inan@aicodix.de>
Date: Wed, 10 Jun 2020 18:32:52 +0200
Subject: [PATCH] print histogram of distances and verify T

---
 tests/short_bch_code_encoder_test.cc | 50 +++++++++++++++++++---------
 1 file changed, 35 insertions(+), 15 deletions(-)

diff --git a/tests/short_bch_code_encoder_test.cc b/tests/short_bch_code_encoder_test.cc
index b6b417a..7a87a9a 100644
--- a/tests/short_bch_code_encoder_test.cc
+++ b/tests/short_bch_code_encoder_test.cc
@@ -8,31 +8,51 @@ Copyright 2020 Ahmet Inan <inan@aicodix.de>
 #include <iostream>
 #include "short_bch_code_encoder.hh"
 
+template<typename TYPE>
+int popcnt(TYPE x)
+{
+	int cnt = 0;
+	while (x) {
+		++cnt;
+		x &= x-1;
+	}
+	return cnt;
+}
+
+template <int N, int K, int T, int POLY>
+void bch_test(int message, int target)
+{
+	CODE::ShortBCHCodeEncoder<N, K> encode(POLY);
+	int hist[N+1] = { 0 };
+	for (int j = 0; j < (1 << K); ++j)
+		for (int i = j + 1; i < (1 << K); ++i)
+			++hist[popcnt(encode(i)^encode(j))];
+	std::cout << "BCH(" << N << ", " << K << ") T=" << T << " hist:";
+	for (int i = 0; i < N + 1; ++i)
+		if (hist[i])
+			std::cout << " " << i << ":" << hist[i];
+	std::cout << std::endl;
+	int d = 0;
+	while (!hist[d])
+		++d;
+	assert((d-1)/2 == T);
+	int codeword = encode(message);
+	assert(target == codeword);
+}
+
 int main()
 {
 	if (1) {
 		// Perfect binary Golay code using x^11+x^9+x^7+x^6+x^5+x+1
-		CODE::ShortBCHCodeEncoder<23, 12> encode(0b101011100011);
-		int message = 0b101011011011;
-		int target = 0b10101101101111011111001;
-		int codeword = encode(message);
-		assert(target == codeword);
+		bch_test<23, 12, 3, 0b101011100011>(0b101011011011, 0b10101101101111011111001);
 	}
 	if (1) {
 		// Perfect binary Golay code using x^11+x^10+x^6+x^5+x^4+x^2+1
-		CODE::ShortBCHCodeEncoder<23, 12> encode(0b110001110101);
-		int message = 0b101011011011;
-		int target = 0b10101101101100100010101;
-		int codeword = encode(message);
-		assert(target == codeword);
+		bch_test<23, 12, 3, 0b110001110101>(0b101011011011, 0b10101101101100100010101);
 	}
 	if (1) {
 		// NASA INTRO BCH(15, 5) T=3
-		CODE::ShortBCHCodeEncoder<15, 5> encode(0b10100110111);
-		int message = 0b11001;
-		int target = 0b110010001111010;
-		int codeword = encode(message);
-		assert(target == codeword);
+		bch_test<15, 5, 3, 0b10100110111>(0b11001, 0b110010001111010);
 	}
 	std::cerr << "Short BCH code encoder test passed!" << std::endl;
 	return 0;