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#include "coding/arithmetic_codec.hpp"
#include "coding/writer.hpp"
#include "coding/reader.hpp"
#include "base/assert.hpp"
#include "base/bits.hpp"
vector<uint32_t> FreqsToDistrTable(vector<uint32_t> const & origFreqs)
{
uint64_t freqLowerBound = 0;
while (1)
{
// Resulting distr table is initialized with first zero value.
vector<uint64_t> result(1, 0);
vector<uint32_t> freqs;
uint64_t sum = 0;
uint64_t minFreq = ~uint64_t(0);
for (uint32_t i = 0; i < origFreqs.size(); ++i)
{
uint32_t freq = origFreqs[i];
if (freq > 0 && freq < minFreq) minFreq = freq;
if (freq > 0 && freq < freqLowerBound) freq = freqLowerBound;
freqs.push_back(freq);
sum += freq;
result.push_back(sum);
}
if (freqLowerBound == 0) freqLowerBound = minFreq;
// This flag shows that some interval with non-zero freq has
// degraded to zero interval in normalized distribution table.
bool hasDegradedZeroInterval = false;
for (uint32_t i = 1; i < result.size(); ++i)
{
result[i] = (result[i] << DISTR_SHIFT) / sum;
if (freqs[i - 1] > 0 && (result[i] - result[i - 1] == 0))
{
hasDegradedZeroInterval = true;
break;
}
}
if (!hasDegradedZeroInterval) return vector<uint32_t>(result.begin(), result.end());
++freqLowerBound;
}
}
ArithmeticEncoder::ArithmeticEncoder(vector<uint32_t> const & distrTable)
: m_begin(0), m_size(-1), m_distrTable(distrTable) {}
void ArithmeticEncoder::Encode(uint32_t symbol)
{
CHECK_LESS(symbol + 1, m_distrTable.size(), ());
uint32_t distrBegin = m_distrTable[symbol];
uint32_t distrEnd = m_distrTable[symbol + 1];
CHECK_LESS(distrBegin, distrEnd, ());
uint32_t prevBegin = m_begin;
m_begin += (m_size >> DISTR_SHIFT) * distrBegin;
m_size = (m_size >> DISTR_SHIFT) * (distrEnd - distrBegin);
if (m_begin < prevBegin) PropagateCarry();
while (m_size < (uint32_t(1) << 24))
{
m_output.push_back(uint8_t(m_begin >> 24));
m_begin <<= 8;
m_size <<= 8;
}
}
vector<uint8_t> ArithmeticEncoder::Finalize()
{
CHECK_GREATER(m_size, 0, ());
uint32_t last = m_begin + m_size - 1;
if (last < m_begin)
{
PropagateCarry();
}
else
{
uint32_t resultHiBits = bits::NumHiZeroBits32(m_begin ^ last) + 1;
uint32_t value = last & (~uint32_t(0) << (32 - resultHiBits));
while (value != 0)
{
m_output.push_back(uint8_t(value >> 24));
value <<= 8;
}
}
m_begin = 0;
m_size = 0;
return m_output;
}
void ArithmeticEncoder::PropagateCarry()
{
int i = m_output.size() - 1;
while (i >= 0 && m_output[i] == 0xFF)
{
m_output[i] = 0;
--i;
}
CHECK_GREATER_OR_EQUAL(i, 0, ());
++m_output[i];
}
ArithmeticDecoder::ArithmeticDecoder(Reader & reader, vector<uint32_t> const & distrTable)
: m_codeValue(0), m_size(-1), m_reader(reader), m_serialCur(0),
m_serialEnd(reader.Size()), m_distrTable(distrTable)
{
for (uint32_t i = 0; i < sizeof(m_codeValue); ++i)
{
m_codeValue <<= 8;
m_codeValue |= ReadCodeByte();
}
}
uint32_t ArithmeticDecoder::Decode()
{
uint32_t l = 0, r = m_distrTable.size(), m = 0;
uint32_t shiftedSize = m_size >> DISTR_SHIFT;
while (r - l > 1)
{
m = (l + r) / 2;
uint32_t intervalBegin = shiftedSize * m_distrTable[m];
if (intervalBegin <= m_codeValue) l = m; else r = m;
}
uint32_t symbol = l;
m_codeValue -= shiftedSize * m_distrTable[symbol];
m_size = shiftedSize * (m_distrTable[symbol + 1] - m_distrTable[symbol]);
while (m_size < (uint32_t(1) << 24))
{
m_codeValue <<= 8;
m_size <<= 8;
m_codeValue |= ReadCodeByte();
}
return symbol;
}
uint8_t ArithmeticDecoder::ReadCodeByte()
{
if (m_serialCur >= m_serialEnd) return 0;
else
{
uint8_t result = 0;
m_reader.Read(m_serialCur, &result, 1);
++m_serialCur;
return result;
}
}
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