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