Add randomized error test for convolution encode/decode.

Signed-off-by: Stefan Westerfeld <stefan@space.twc.de>

src/convcode.cc

@@ -4,6 +4,7 @@
 #include <assert.h>
 
 using std::vector;
+using std::string;
 
 int
 parity (unsigned int v)
@@ -88,27 +89,81 @@ conv_decode (const vector<int>& coded_bits)
   return decoded_bits;
 }
 
+vector<int>
+generate_error_vector (size_t n, int errors)
+{
+  vector<int> ev (n);
+
+  while (errors)
+    {
+      size_t pos = rand() % ev.size();
+      if (ev[pos] != 1)
+        {
+          ev[pos] = 1;
+          errors--;
+        }
+    }
+  return ev;
+}
 int
-main()
+main (int argc, char **argv)
 {
-  vector<int> in_bits = bit_str_to_vec ("80f12381");
-
-  printf ("input vector (k=%zd):  ", in_bits.size());
-  for (auto b : in_bits)
-    printf ("%d", b);
-  printf ("\n");
-
-  vector<int> coded_bits = conv_encode (in_bits);
-  printf ("coded vector (n=%zd): ", coded_bits.size());
-  for (auto b : coded_bits)
-    printf ("%d", b);
-  printf ("\n");
-
-  printf ("coded hex: %s\n", bit_vec_to_str (coded_bits).c_str());
-
-  vector<int> decoded_bits = conv_decode (coded_bits);
-  printf ("output vector (k=%zd): ", decoded_bits.size());
-  for (auto b : decoded_bits)
-    printf ("%d", b);
-  printf ("\n");
+  if (argc == 1)
+    {
+      vector<int> in_bits = bit_str_to_vec ("80f12381");
+
+      printf ("input vector (k=%zd):  ", in_bits.size());
+      for (auto b : in_bits)
+        printf ("%d", b);
+      printf ("\n");
+
+      vector<int> coded_bits = conv_encode (in_bits);
+      printf ("coded vector (n=%zd): ", coded_bits.size());
+      for (auto b : coded_bits)
+        printf ("%d", b);
+      printf ("\n");
+
+      printf ("coded hex: %s\n", bit_vec_to_str (coded_bits).c_str());
+
+      vector<int> decoded_bits = conv_decode (coded_bits);
+      printf ("output vector (k=%zd): ", decoded_bits.size());
+      for (auto b : decoded_bits)
+        printf ("%d", b);
+      printf ("\n");
+    }
+  if (argc == 2 && string (argv[1]) == "error")
+    {
+      for (size_t bit_errors = 0; bit_errors < 100; bit_errors++)
+        {
+          size_t coded_bit_count = 0;
+          int bad_decode = 0;
+          constexpr int test_size = 1000;
+
+          for (int i = 0; i < test_size; i++)
+            {
+              vector<int> in_bits;
+              while (in_bits.size() != 128)
+                in_bits.push_back (rand() & 1);
+
+              vector<int> coded_bits = conv_encode (in_bits);
+              coded_bit_count = coded_bits.size();
+
+              vector<int> error_bits = generate_error_vector (coded_bits.size(), bit_errors);
+              for (size_t pos = 0; pos < coded_bits.size(); pos++)
+                coded_bits[pos] ^= error_bits[pos];
+
+              vector<int> decoded_bits = conv_decode (coded_bits);
+
+              assert (decoded_bits.size() == 128);
+
+              int errors = 0;
+              for (size_t i = 0; i < 128; i++)
+                if (decoded_bits[i] != in_bits[i])
+                  errors++;
+              if (errors > 0)
+                bad_decode++;
+            }
+          printf ("%f %f\n", (100.0 * bit_errors) / coded_bit_count, (100.0 * bad_decode) / test_size);
+        }
+    }
 }