Add test for soft decoding.

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

src/testconvcode.cc

 #include "utils.hh"
 #include "convcode.hh"
 
+#include <random>
+
 #include <assert.h>
 
 using std::vector;
@@ -89,4 +91,60 @@ main (int argc, char **argv)
           printf ("%f %f\n", (100.0 * bit_errors) / coded_bit_count, (100.0 * bad_decode) / test_size);
         }
     }
+  if (argc == 2 && string (argv[1]) == "soft-error")
+    {
+      for (double stddev = 0; stddev < 1; stddev += 0.01)
+        {
+          size_t coded_bit_count = 0;
+          int bad_decode1 = 0, bad_decode2 = 0;
+          constexpr int test_size = 20;
+
+          int local_be = 0;
+          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();
+
+              std::default_random_engine generator;
+              std::normal_distribution<double> dist (0, stddev);
+
+              vector<float> recv_bits;
+              for (auto b : coded_bits)
+                recv_bits.push_back (b + dist (generator));
+
+              vector<int> decoded_bits1 = conv_decode_soft (recv_bits);
+
+              vector<int> recv_hard_bits;
+              for (auto b : recv_bits)
+                recv_hard_bits.push_back ((b > 0.5) ? 1 : 0);
+
+              for (size_t x = 0; x < recv_hard_bits.size(); x++)
+                local_be += coded_bits[x] ^ recv_hard_bits[x];
+
+              vector<int> decoded_bits2 = conv_decode_hard (recv_hard_bits);
+
+              assert (decoded_bits1.size() == 128);
+              assert (decoded_bits2.size() == 128);
+
+              int e1 = 0;
+              int e2 = 0;
+              for (size_t i = 0; i < 128; i++)
+                {
+                  if (decoded_bits1[i] != in_bits[i])
+                    e1++;
+                  if (decoded_bits2[i] != in_bits[i])
+                    e2++;
+                }
+              if (e1)
+                bad_decode1++;
+              if (e2)
+                bad_decode2++;
+            }
+          printf ("%f %f %f\n", double (100 * local_be) / test_size / coded_bit_count, (100.0 * bad_decode1) / test_size, (100.0 * bad_decode2) / test_size);
+        }
+    }
 }