Add optional erasure positions to RS decoder

src/core/system_parameters/reed_solomon.cc

@@ -540,26 +540,24 @@ void ReedSolomon::encode_rs_8(const uint8_t* data, uint8_t* parity) const
 }
 
 
-int ReedSolomon::decode(std::vector<uint8_t>& data_to_decode) const
+int ReedSolomon::decode(std::vector<uint8_t>& data_to_decode, const std::vector<int>& erasure_positions) const
 {
     if (data_to_decode.size() != d_symbols_per_block)
         {
             std::cerr << "Reed Solomon error: bad input length\n";
             return -1;
         }
-    std::vector<uint8_t> decoded_data(d_data_in_block, 0);
+    int result = decode_rs_8(data_to_decode.data(), erasure_positions.data(), erasure_positions.size(), d_pad);
-    int result = decode_rs_8(data_to_decode.data(), nullptr, 0, d_pad);
     return result;
 }
 
 
-int ReedSolomon::decode_rs_8(uint8_t* data, int* eras_pos, int no_eras, int pad) const
+int ReedSolomon::decode_rs_8(uint8_t* data, const int* eras_pos, int no_eras, int pad) const
 {
     if (pad < 0 || pad > 222)
         {
             return -1;
         }
-    int retval;
     int deg_lambda;
     int el;
     int deg_omega;
@@ -621,16 +619,7 @@ int ReedSolomon::decode_rs_8(uint8_t* data, int* eras_pos, int no_eras, int pad)
         {
             // if syndrome is zero, data[] is a codeword and there are no
             // errors to correct. So return data[] unmodified
-            count = 0;
+            return 0;
-            if (eras_pos != nullptr)
-                {
-                    for (i = 0; i < count; i++)
-                        {
-                            eras_pos[i] = loc[i];
-                        }
-                }
-            retval = count;
-            return retval;
         }
 
     memset(&lambda[1], 0, d_nroots * sizeof(lambda[0]));
@@ -761,16 +750,7 @@ int ReedSolomon::decode_rs_8(uint8_t* data, int* eras_pos, int no_eras, int pad)
         {
             // deg(lambda) unequal to number of roots => uncorrectable
             // error detected
-            count = -1;
+            return -1;
-            if (eras_pos != nullptr)
-                {
-                    for (i = 0; i < count; i++)
-                        {
-                            eras_pos[i] = loc[i];
-                        }
-                }
-            retval = count;
-            return retval;
         }
 
     // Compute err+eras evaluator poly omega(x) = s(x)*lambda(x) (modulo
@@ -821,14 +801,5 @@ int ReedSolomon::decode_rs_8(uint8_t* data, int* eras_pos, int no_eras, int pad)
                 }
         }
 
-    if (eras_pos != nullptr)
+    return count;
-        {
-            for (i = 0; i < count; i++)
-                {
-                    eras_pos[i] = loc[i];
-                }
-        }
-    retval = count;
-
-    return retval;
 }

src/core/system_parameters/reed_solomon.h

@@ -79,11 +79,18 @@ public:
         const std::vector<std::vector<uint8_t>>& gen_matrix = std::vector<std::vector<uint8_t>>{});
 
     /*!
-     * \brief Decode an encoded block. The decoded symbols are at the first
+     * \brief Decode an encoded block.
-     * 255-nroots elements of the input vector. Returns the number of corrected
+     *
-     * errors or -1 if decoding failed.
+     * The decoded symbols are at the first 255-nroots elements
+     * of the input vector.
+     *
+     * The second parameter is optional, and contains a vector of erasure
+     * positions to be passed to the decoding algorithm.
+     *
+     * Returns the number of corrected errors or -1 if decoding failed.
      */
-    int decode(std::vector<uint8_t>& data_to_decode) const;
+    int decode(std::vector<uint8_t>& data_to_decode,
+        const std::vector<int>& erasure_positions = std::vector<int>{}) const;
 
     /*!
      * \brief Encode data with the generator matrix (for testing purposes)
@@ -98,7 +105,7 @@ public:
 private:
     static const int d_symbols_per_block = 255;  // the total number of symbols in a RS block.
 
-    int decode_rs_8(uint8_t* data, int* eras_pos, int no_eras, int pad) const;
+    int decode_rs_8(uint8_t* data, const int* eras_pos, int no_eras, int pad) const;
     int mod255(int x) const;
     int rs_min(int a, int b) const;
 

src/tests/unit-tests/system-parameters/galileo_e6b_reed_solomon_test.cc

@@ -493,3 +493,45 @@ TEST(ReedSolomonTest, Decode111ErrorsCustomConstructor)
     std::vector<uint8_t> decoded(encoded_input.begin(), encoded_input.begin() + 32);
     EXPECT_TRUE(expected_output == decoded);
 }
+
+
+TEST(ReedSolomonTest, Decode112Errors)
+{
+    std::vector<uint8_t> encoded_input = {
+        71, 12, 25, 210, 178, 81, 243, 9, 112, 98, 196, 203, 48, 125, 114, 165, 181, 193, 71, 174, 168, 42, 31, 128, 245, 87, 150, 58, 192, 66, 130, 179, 133, 210, 122, 224, 75, 138, 20, 205, 14, 245, 209, 187, 246, 228, 12, 39, 244, 238, 223, 217, 84, 233, 137, 168, 153, 8, 94, 26, 99, 169, 149, 203, 115, 69, 211, 43, 70, 96, 70, 38, 160, 1, 232, 153, 223, 165, 93, 205, 101, 170, 60, 188, 198, 82, 168, 79, 95, 23, 118, 215, 187, 136, 24, 99, 252, 3, 144, 166, 117, 45, 168, 239, 77, 42, 246, 33, 122, 97, 242, 236, 13, 217, 96, 186, 71, 250, 242, 177, 125, 87, 27, 13, 118, 181, 178, 12, 27, 66, 31, 74, 127, 46, 112, 127, 116, 122, 190, 71, 240, 95, 78, 194, 113, 80, 46, 126, 74, 136, 118, 133, 105, 176, 47, 230, 162, 195, 93, 157, 72, 119, 13, 232, 151, 200, 191, 143, 75, 161, 111, 29, 158, 16, 181, 165, 92, 39, 17, 218, 228, 58, 176, 233, 55, 211, 195, 73, 37, 137, 232, 241, 150, 236, 152, 153, 53, 74, 81, 91, 160, 244, 21, 95, 176, 179, 141, 39, 61, 136, 16, 58, 160, 51, 210, 31, 134, 63, 203, 96, 219, 44, 231, 61, 220, 0, 241, 220, 207, 17, 52, 150, 117, 54, 222, 128, 101, 213, 164, 234, 74, 224, 57, 246, 70, 27, 202, 229, 4, 243, 128, 211, 158, 199, 4};
+
+    // Introduce 112 errors (this should make the decoder fail):
+    for (int i = 0; i < 224; i += 2)
+        {
+            encoded_input[i] = 0;
+        }
+
+    auto rs = std::make_unique<ReedSolomon>();
+
+    int result = rs->decode(encoded_input);
+    EXPECT_TRUE(result == -1);
+}
+
+
+TEST(ReedSolomonTest, Decode113ErrorsWithErasure)
+{
+    std::vector<uint8_t> expected_output = {71, 12, 25, 210, 178, 81, 243, 9, 112, 98, 196, 203, 48, 125, 114, 165, 181, 193, 71, 174, 168, 42, 31, 128, 245, 87, 150, 58, 192, 66, 130, 179};
+
+    std::vector<uint8_t> encoded_input = {
+        71, 12, 25, 210, 178, 81, 243, 9, 112, 98, 196, 203, 48, 125, 114, 165, 181, 193, 71, 174, 168, 42, 31, 128, 245, 87, 150, 58, 192, 66, 130, 179, 133, 210, 122, 224, 75, 138, 20, 205, 14, 245, 209, 187, 246, 228, 12, 39, 244, 238, 223, 217, 84, 233, 137, 168, 153, 8, 94, 26, 99, 169, 149, 203, 115, 69, 211, 43, 70, 96, 70, 38, 160, 1, 232, 153, 223, 165, 93, 205, 101, 170, 60, 188, 198, 82, 168, 79, 95, 23, 118, 215, 187, 136, 24, 99, 252, 3, 144, 166, 117, 45, 168, 239, 77, 42, 246, 33, 122, 97, 242, 236, 13, 217, 96, 186, 71, 250, 242, 177, 125, 87, 27, 13, 118, 181, 178, 12, 27, 66, 31, 74, 127, 46, 112, 127, 116, 122, 190, 71, 240, 95, 78, 194, 113, 80, 46, 126, 74, 136, 118, 133, 105, 176, 47, 230, 162, 195, 93, 157, 72, 119, 13, 232, 151, 200, 191, 143, 75, 161, 111, 29, 158, 16, 181, 165, 92, 39, 17, 218, 228, 58, 176, 233, 55, 211, 195, 73, 37, 137, 232, 241, 150, 236, 152, 153, 53, 74, 81, 91, 160, 244, 21, 95, 176, 179, 141, 39, 61, 136, 16, 58, 160, 51, 210, 31, 134, 63, 203, 96, 219, 44, 231, 61, 220, 0, 241, 220, 207, 17, 52, 150, 117, 54, 222, 128, 101, 213, 164, 234, 74, 224, 57, 246, 70, 27, 202, 229, 4, 243, 128, 211, 158, 199, 4};
+
+    // Introduce 113 errors:
+    for (int i = 0; i < 226; i += 2)
+        {
+            encoded_input[i] = 0;
+        }
+
+    std::vector<int> erasure_positions{2, 4, 16, 18, 22, 54};
+
+    auto rs = std::make_unique<ReedSolomon>();
+
+    int result = rs->decode(encoded_input, erasure_positions);
+    EXPECT_TRUE(result == 113);
+    std::vector<uint8_t> decoded(encoded_input.begin(), encoded_input.begin() + 32);
+    EXPECT_TRUE(expected_output == decoded);
+}