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tdfec/td/fec/algebra/BeliefPropagationDecoding.cpp

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+/*
+    This file is part of TON Blockchain Library.
+
+    TON Blockchain Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 2 of the License, or
+    (at your option) any later version.
+
+    TON Blockchain Library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with TON Blockchain Library.  If not, see <http://www.gnu.org/licenses/>.
+
+    Copyright 2017-2019 Telegram Systems LLP
+*/
+#include "td/fec/algebra/BeliefPropagationDecoding.h"
+
+namespace td {
+BeliefPropagationDecoding::BeliefPropagationDecoding(size_t symbols_count, size_t symbol_size)
+    : max_equation_count_{static_cast<size_t>(static_cast<double>(symbols_count) * 1.1 + 5)}
+    , C_{symbols_count, symbol_size}
+    , D_{max_equation_count_, symbol_size} {
+  equations_.reserve(max_equation_count_);
+  symbols_.resize(symbols_count);
+
+  edges_.resize(1);
+}
+
+Slice BeliefPropagationDecoding::get_symbol(uint32 symbol_id) const {
+  CHECK(symbols_[symbol_id].is_ready);
+  return C_.row(symbol_id);
+}
+
+void BeliefPropagationDecoding::add_equation(Span<uint32> symbol_ids, Slice data) {
+  if (equations_.size() >= D_.rows()) {
+    MatrixGF256 new_D(D_.rows() * 2, D_.cols());
+    new_D.set_from(D_, 0, 0);
+    D_ = std::move(new_D);
+  }
+  CHECK(symbol_ids.size() != 0);
+
+  uint32 equation_id = static_cast<uint32>(equations_.size());
+  D_.row_set(equation_id, data);
+
+  EquationInfo equation;
+  for (auto symbol_id : symbol_ids) {
+    CHECK(symbol_id < symbols_.size());
+    auto &symbol = symbols_[symbol_id];
+    if (symbol.is_ready) {
+      D_.row_add(equation_id, C_.row(symbol_id));
+    } else {
+      equation.symbols_xor ^= symbol_id;
+      equation.symbols_count++;
+
+      edges_.push_back({equation_id, symbol.head_});
+      symbol.head_ = uint32(edges_.size() - 1);
+    }
+  }
+
+  if (equation.symbols_count == 0) {
+    return;
+  }
+
+  equations_.push_back(equation);
+  if (equation.symbols_count == 1) {
+    ready_equations_.push_back(equation_id);
+    loop();
+  }
+}
+bool BeliefPropagationDecoding::is_ready() const {
+  return ready_symbols().size() == C_.rows();
+}
+
+Span<uint32> BeliefPropagationDecoding::ready_symbols() const {
+  return ready_symbols_;
+}
+
+void BeliefPropagationDecoding::loop() {
+  while (!is_ready() && !ready_equations_.empty()) {
+    auto equation_id = ready_equations_.back();
+    ready_equations_.pop_back();
+    auto &equation = equations_[equation_id];
+    LOG_CHECK(equation.symbols_count <= 1) << equation.symbols_count;
+    if (equation.symbols_count == 0) {
+      continue;
+    }
+    auto symbol_id = equation.symbols_xor;
+    auto &symbol = symbols_[symbol_id];
+    LOG_CHECK(symbol_id < symbols_.size())
+        << equation.symbols_xor << " " << equation.symbols_count << " " << equation_id;
+    if (symbol.is_ready) {
+      continue;
+    }
+    C_.row_set(symbol_id, D_.row(equation_id));
+    symbol.is_ready = true;
+    ready_symbols_.push_back(symbol_id);
+    for (auto i = symbol.head_; i != 0;) {
+      auto &edge = edges_[i];
+      auto next_equation_id = edge.value;
+      i = edge.next;
+      D_.row_add(next_equation_id, C_.row(symbol_id));
+      auto &next_equation = equations_[next_equation_id];
+      next_equation.symbols_xor ^= symbol_id;
+      next_equation.symbols_count--;
+      if (next_equation.symbols_count == 1) {
+        ready_equations_.push_back(next_equation_id);
+      }
+    }
+  }
+}
+}  // namespace td