From 1f956f56bde94115e2cd6c384633efcc56150d73 Mon Sep 17 00:00:00 2001
From: csrichter <csrichter@hotmail.de>
Date: Tue, 2 May 2017 15:03:11 +0200
Subject: [PATCH] added calcSyndrome_vec from redsea, TODO: compare with
 "calc_syndrome" which is faster and if they have the same result

---
 lib/rds_decoder_redsea_impl.cc | 35 +++++++++++++++++++++++++++++-----
 1 file changed, 30 insertions(+), 5 deletions(-)

diff --git a/lib/rds_decoder_redsea_impl.cc b/lib/rds_decoder_redsea_impl.cc
index e6d0179..384da0a 100644
--- a/lib/rds_decoder_redsea_impl.cc
+++ b/lib/rds_decoder_redsea_impl.cc
@@ -120,6 +120,30 @@ uint16_t rds_decoder_redsea_impl::calc_syndrome(uint32_t message,uint8_t mlen) {
 }
 
 //redsea stuff:
+// Section B.1.1: '-- calculated by the modulo-two addition of all the rows of
+// the -- matrix for which the corresponding coefficient in the -- vector is 1.'
+uint32_t matrixMultiply(uint32_t vec, const std::vector<uint32_t>& matrix) {
+  uint32_t result = 0;
+
+  for (size_t k=0; k < matrix.size(); k++)
+    if ((vec >> k) & 0x01)
+      result ^= matrix[matrix.size() - 1 - k];
+
+  return result;
+}
+
+// Section B.2.1: 'The calculation of the syndromes -- can easily be done by
+// multiplying each word with the parity matrix H.'
+uint32_t calcSyndrome_vec(uint32_t vec) {
+  static const std::vector<uint32_t> parity_check_matrix({
+      0x200, 0x100, 0x080, 0x040, 0x020, 0x010, 0x008, 0x004,
+      0x002, 0x001, 0x2dc, 0x16e, 0x0b7, 0x287, 0x39f, 0x313,
+      0x355, 0x376, 0x1bb, 0x201, 0x3dc,
+      0x1ee, 0x0f7, 0x2a7, 0x38f, 0x31b
+  });
+
+  return matrixMultiply(vec, parity_check_matrix);
+}
 const unsigned kBitmask16 = 0x000FFFF;
 const unsigned kBitmask26 = 0x3FFFFFF;
 const unsigned kBitmask28 = 0xFFFFFFF;
@@ -144,8 +168,8 @@ static const char * const offset_name[]={"A","B","C","D","c"};*/
     for (uint32_t e : {0x1,0x3}) {//fix up to 2-bit burst errors (as book says)
       for (int shift=0; shift < 26; shift++) {
         uint32_t errvec = ((e << shift) & kBitmask26);
-        //uint16_t sy = calc_syndrome(errvec ^ offset_word[offset_num],26);
         uint32_t sy = calc_syndrome(errvec ^ offset_word[offset_num],26);//why uint32 and not uint16 as everywhere else???
+        //uint32_t sy = calcSyndrome_vec(errvec ^ offset_word[offset_num]);
         result.insert({{sy, offset_name[offset_num]}, errvec});
         //dout << "adding  sy:"<<sy<<"\t\toffset:"<<offset_name[offset_num]<<"\terrvec:"<<std::bitset<32>(errvec) <<std::endl;
       }
@@ -155,14 +179,15 @@ static const char * const offset_name[]={"A","B","C","D","c"};*/
 }
 
 uint32_t rds_decoder_redsea_impl::correctBurstErrors(uint32_t block, char offset) {
-  uint16_t syndrome = calc_syndrome(block,26);
+  uint32_t syndrome = calc_syndrome(block,26);
+  //uint32_t syndrome = calcSyndrome_vec(block);
   uint32_t corrected_block = block;
   //dout << "trying to correct sy:"<<syndrome<<"\t\toffset:"<<offset;//<<std::endl;
   //dout << "\tcount:"<<kErrorLookup.count({(uint16_t)syndrome, (char)offset})<<std::endl;
-  if (kErrorLookup.count({(uint16_t)syndrome, (char)offset}) > 0) {
-    uint32_t err = kErrorLookup.at({(uint16_t)syndrome, (char)offset});
+  if (kErrorLookup.count({syndrome, offset}) > 0) {
+    uint32_t err = kErrorLookup.at({syndrome, offset});
     //dout << "correcting"<<std::endl;
-    err=0;//correction disabled
+    //err=0;//correction disabled
     corrected_block ^= err;
     
   }