New cpp folder structure

Signed-off-by: Alexander Borsuk <me@alex.bio>

libs/coding/simple_dense_coding.cpp

@@ -0,0 +1,65 @@
+#include "coding/simple_dense_coding.hpp"
+
+#include "base/assert.hpp"
+
+#include <algorithm>
+#include <limits>
+
+#if defined(__clang__)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunused-local-typedef"
+#endif
+
+#include <boost/range/adaptor/transformed.hpp>
+
+#if defined(__clang__)
+#pragma clang diagnostic pop
+#endif
+
+namespace coding
+{
+
+SimpleDenseCoding::SimpleDenseCoding(std::vector<uint8_t> const & data)
+{
+  size_t constexpr kAlphabetSize = size_t(std::numeric_limits<uint8_t>::max()) + 1;
+
+  uint64_t frequency[kAlphabetSize] = { 0 };  // Maps symbols to frequences.
+  for (uint8_t symbol : data)
+    ++frequency[symbol];
+
+  uint8_t symbols[kAlphabetSize];  // Maps ranks to symbols.
+  uint8_t rank[kAlphabetSize];     // Maps symbols to ranks.
+
+  for (size_t i = 0; i < kAlphabetSize; ++i)
+    symbols[i] = i;
+
+  auto frequencyCmp = [&frequency](uint8_t lsym, uint8_t rsym)
+  {
+    return frequency[lsym] > frequency[rsym];
+  };
+  std::sort(symbols, symbols + kAlphabetSize, frequencyCmp);
+  for (size_t r = 0; r < kAlphabetSize; ++r)
+    rank[symbols[r]] = r;
+
+  auto getRank = [&rank](uint8_t sym)
+  {
+    return rank[sym];
+  };
+
+  using namespace boost::adaptors;
+  succinct::elias_fano_compressed_list(data | transformed(getRank)).swap(m_ranks);
+  m_symbols.assign(symbols);
+}
+
+SimpleDenseCoding::SimpleDenseCoding(SimpleDenseCoding && rhs)
+{
+  m_ranks.swap(rhs.m_ranks);
+  m_symbols.swap(rhs.m_symbols);
+}
+
+uint8_t SimpleDenseCoding::Get(uint64_t i) const
+{
+  ASSERT_LESS(i, Size(), ());
+  return m_symbols[m_ranks[static_cast<size_t>(i)]];
+}
+}  // namespace coding