1 files changed, 122 insertions, 0 deletions
diff --git a/lib/edi/Interleaver.cpp b/lib/edi/Interleaver.cpp
new file mode 100644
index 0000000..f26a50e
--- /dev/null
+++ b/lib/edi/Interleaver.cpp
@@ -0,0 +1,122 @@
+/*
+   Copyright (C) 2017
+   Matthias P. Braendli, matthias.braendli@mpb.li
+
+    http://www.opendigitalradio.org
+
+   EDI output,
+   Interleaving of PFT fragments to increase robustness against
+   burst packet loss.
+
+   This is possible because EDI has to assume that fragments may reach
+   the receiver out of order.
+
+   */
+/*
+   This file is part of ODR-DabMux.
+
+   ODR-DabMux is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as
+   published by the Free Software Foundation, either version 3 of the
+   License, or (at your option) any later version.
+
+   ODR-DabMux 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with ODR-DabMux.  If not, see <http://www.gnu.org/licenses/>.
+   */
+
+#include "Interleaver.h"
+#include <cassert>
+
+namespace edi {
+
+void Interleaver::SetLatency(size_t latency_frames)
+{
+    m_latency = latency_frames;
+}
+
+Interleaver::fragment_vec Interleaver::Interleave(fragment_vec &fragments)
+{
+    m_fragment_count = fragments.size();
+
+    // Create vectors containing Fcount*latency fragments in total
+    // and store them into the deque
+    if (m_buffer.empty()) {
+        m_buffer.emplace_back();
+    }
+
+    auto& last_buffer = m_buffer.back();
+
+    for (auto& fragment : fragments) {
+        const bool last_buffer_is_complete =
+                (last_buffer.size() >= m_fragment_count * m_latency);
+
+        if (last_buffer_is_complete) {
+            m_buffer.emplace_back();
+            last_buffer = m_buffer.back();
+        }
+
+        last_buffer.push_back(std::move(fragment));
+    }
+
+    fragments.clear();
+
+    while ( not m_buffer.empty() and
+            (m_buffer.front().size() >= m_fragment_count * m_latency)) {
+
+        auto& first_buffer = m_buffer.front();
+
+        assert(first_buffer.size() == m_fragment_count * m_latency);
+
+        /* Assume we have 5 fragments per AF frame, and latency of 3.
+         * This will give the following strides:
+         *    0        1     2
+         * +-------+-------+---+
+         * | 0   1 | 2   3 | 4 |
+         * |       |   +---+   |
+         * | 5   6 | 7 | 8   9 |
+         * |   +---+   |       |
+         * |10 |11  12 |13  14 |
+         * +---+-------+-------+
+         *
+         * ix will be 0, 5, 10, 1, 6 in the first loop
+         */
+
+        for (size_t i = 0; i < m_fragment_count; i++) {
+            const size_t ix = m_interleave_offset + m_fragment_count * m_stride;
+            m_interleaved_fragments.push_back(first_buffer.at(ix));
+
+            m_stride += 1;
+            if (m_stride >= m_latency) {
+                m_interleave_offset++;
+                m_stride = 0;
+            }
+        }
+
+        if (m_interleave_offset >= m_fragment_count) {
+            m_interleave_offset = 0;
+            m_stride = 0;
+            m_buffer.pop_front();
+        }
+    }
+
+    std::vector<PFTFragment> interleaved_frags;
+
+    const size_t n = std::min(m_fragment_count, m_interleaved_fragments.size());
+    std::move(m_interleaved_fragments.begin(),
+              m_interleaved_fragments.begin() + n,
+              std::back_inserter(interleaved_frags));
+    m_interleaved_fragments.erase(
+              m_interleaved_fragments.begin(),
+              m_interleaved_fragments.begin() + n);
+
+    return interleaved_frags;
+}
+
+}
+
+