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/*

* Reference arithmetic coding

*

* Copyright (c) Project Nayuki

* MIT License. See readme file.

* https://www.nayuki.io/page/reference-arithmetic-coding

*/

#include <stdexcept>

#include "FrequencyTable.hpp"

using std::uint32_t;

FrequencyTable::~FrequencyTable() {}

FlatFrequencyTable::FlatFrequencyTable(uint32_t numSyms) :

numSymbols(numSyms) {

if (numSyms < 1)

throw std::domain_error("Number of symbols must be positive");

}

uint32_t FlatFrequencyTable::getSymbolLimit() const {

return numSymbols;

}

uint32_t FlatFrequencyTable::get(uint32_t symbol) const {

checkSymbol(symbol);

return 1;

}

uint32_t FlatFrequencyTable::getTotal() const {

return numSymbols;

}

uint32_t FlatFrequencyTable::getLow(uint32_t symbol) const {

checkSymbol(symbol);

return symbol;

}

uint32_t FlatFrequencyTable::getHigh(uint32_t symbol) const {

checkSymbol(symbol);

return symbol + 1;

}

void FlatFrequencyTable::set(uint32_t, uint32_t) {

throw std::logic_error("Unsupported operation");

}

void FlatFrequencyTable::increment(uint32_t) {

throw std::logic_error("Unsupported operation");

}

void FlatFrequencyTable::checkSymbol(uint32_t symbol) const {

if (symbol >= numSymbols)

throw std::domain_error("Symbol out of range");

}

SimpleFrequencyTable::SimpleFrequencyTable(const std::vector<uint32_t> &freqs) {

if (freqs.size() > UINT32_MAX - 1)

throw std::length_error("Too many symbols");

uint32_t size = static_cast<uint32_t>(freqs.size());

if (size < 1)

throw std::invalid_argument("At least 1 symbol needed");

frequencies = freqs;

cumulative.reserve(size + 1);

initCumulative(false);

total = getHigh(size - 1);

}

SimpleFrequencyTable::SimpleFrequencyTable(const FrequencyTable &freqs) {

uint32_t size = freqs.getSymbolLimit();

if (size < 1)

throw std::invalid_argument("At least 1 symbol needed");

if (size > UINT32_MAX - 1)

throw std::length_error("Too many symbols");

frequencies.reserve(size + 1);

for (uint32_t i = 0; i < size; i++)

frequencies.push_back(freqs.get(i));

cumulative.reserve(size + 1);

initCumulative(false);

total = getHigh(size - 1);

}

uint32_t SimpleFrequencyTable::getSymbolLimit() const {

return static_cast<uint32_t>(frequencies.size());

}

uint32_t SimpleFrequencyTable::get(uint32_t symbol) const {

return frequencies.at(symbol);

}

void SimpleFrequencyTable::set(uint32_t symbol, uint32_t freq) {

if (total < frequencies.at(symbol))

throw std::logic_error("Assertion error");

uint32_t temp = total - frequencies.at(symbol);

total = checkedAdd(temp, freq);

frequencies.at(symbol) = freq;

cumulative.clear();

}

void SimpleFrequencyTable::increment(uint32_t symbol) {

if (frequencies.at(symbol) == UINT32_MAX)

throw std::overflow_error("Arithmetic overflow");

total = checkedAdd(total, 1);

frequencies.at(symbol)++;

cumulative.clear();

}

uint32_t SimpleFrequencyTable::getTotal() const {

return total;

}

uint32_t SimpleFrequencyTable::getLow(uint32_t symbol) const {

initCumulative();

return cumulative.at(symbol);

}

uint32_t SimpleFrequencyTable::getHigh(uint32_t symbol) const {

initCumulative();

return cumulative.at(symbol + 1);

}

void SimpleFrequencyTable::initCumulative(bool checkTotal) const {

if (!cumulative.empty())

return;

uint32_t sum = 0;

cumulative.push_back(sum);

for (uint32_t freq : frequencies) {

// This arithmetic should not throw an exception, because invariants are being maintained

// elsewhere in the data structure. This implementation is just a defensive measure.

sum = checkedAdd(freq, sum);

cumulative.push_back(sum);

}

if (checkTotal && sum != total)

throw std::logic_error("Assertion error");

}

uint32_t SimpleFrequencyTable::checkedAdd(uint32_t x, uint32_t y) {

if (x > UINT32_MAX - y)

throw std::overflow_error("Arithmetic overflow");

return x + y;

}