Add conv code api to get the number of coded bits for a fixed message size.

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

src/convcode.cc

@@ -36,6 +36,12 @@ constexpr  auto         generators  = std::array<unsigned,3> { 0552137, 0614671,
 constexpr  unsigned int state_count = (1 << order);
 constexpr  unsigned int state_mask  = (1 << order) - 1;
 
+size_t
+conv_code_size (size_t msg_size)
+{
+  return (msg_size + order) * rate;
+}
+
 vector<int>
 conv_encode (const vector<int>& in_bits)
 {

src/convcode.hh

@@ -4,6 +4,7 @@
 #include <vector>
 #include <string>
 
+size_t           conv_code_size (size_t msg_size);
 std::vector<int> conv_encode (const std::vector<int>& in_bits);
 std::vector<int> conv_decode_hard (const std::vector<int>& coded_bits);
 std::vector<int> conv_decode_soft (const std::vector<float>& coded_bits);

src/testconvcode.cc

@@ -43,6 +43,8 @@ main (int argc, char **argv)
       printf ("\n");
       printf ("coded hex: %s\n", bit_vec_to_str (coded_bits).c_str());
 
+      assert (coded_bits.size() == conv_code_size (in_bits.size()));
+
       vector<int> decoded_bits = conv_decode_hard (coded_bits);
       printf ("output vector (k=%zd): ", decoded_bits.size());
       for (auto b : decoded_bits)