if (numBits < 1 || numBits > 63)

throw std::domain_error("State size out of range");

numStateBits = numBits;

fullRange = static_cast<decltype(fullRange)>(1) << numStateBits;

halfRange = fullRange >> 1; // Non-zero

quarterRange = halfRange >> 1; // Can be zero

minimumRange = quarterRange + 2; // At least 2

maximumTotal = std::min(std::numeric_limits<decltype(fullRange)>::max() / fullRange, minimumRange);

stateMask = fullRange - 1;

low = 0;

high = stateMask;

// State check

if (low >= high || (low & stateMask) != low || (high & stateMask) != high)

throw std::logic_error("Assertion error: Low or high out of range");

uint64_t range = high - low + 1;

if (range < minimumRange || range > fullRange)

throw std::logic_error("Assertion error: Range out of range");

// Frequency table values check

uint32_t total = freqs.getTotal();

uint32_t symLow = freqs.getLow(symbol);

uint32_t symHigh = freqs.getHigh(symbol);

if (symLow == symHigh)

throw std::invalid_argument("Symbol has zero frequency");

if (total > maximumTotal)

throw std::invalid_argument("Cannot code symbol because total is too large");

// Update range

uint64_t newLow = low + symLow * range / total;

uint64_t newHigh = low + symHigh * range / total - 1;

low = newLow;

high = newHigh;

// While low and high have the same top bit value, shift them out

while (((low ^ high) & halfRange) == 0) {

shift();

low = ((low << 1) & stateMask);

high = ((high << 1) & stateMask) | 1;

}

// Now low's top bit must be 0 and high's top bit must be 1

// While low's top two bits are 01 and high's are 10, delete the second highest bit of both

while ((low & ~high & quarterRange) != 0) {

underflow();

low = (low << 1) ^ halfRange;

high = ((high ^ halfRange) << 1) | halfRange | 1;

}

ArithmeticCoderBase(numBits),

input(in),

code(0) {

for (int i = 0; i < numStateBits; i++)

code = code << 1 | readCodeBit();

// Translate from coding range scale to frequency table scale

uint32_t total = freqs.getTotal();

if (total > maximumTotal)

throw std::invalid_argument("Cannot decode symbol because total is too large");

uint64_t range = high - low + 1;

uint64_t offset = code - low;

uint64_t value = ((offset + 1) * total - 1) / range;

if (value * range / total > offset)

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

if (value >= total)

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

// A kind of binary search. Find highest symbol such that freqs.getLow(symbol) <= value.

uint32_t start = 0;

uint32_t end = freqs.getSymbolLimit();

while (end - start > 1) {

uint32_t middle = (start + end) >> 1;

if (freqs.getLow(middle) > value)

end = middle;

else

start = middle;

}

if (start + 1 != end)

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

uint32_t symbol = start;

if (offset < freqs.getLow(symbol) * range / total || freqs.getHigh(symbol) * range / total <= offset)

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

update(freqs, symbol);

if (code < low || code > high)

throw std::logic_error("Assertion error: Code out of range");

return symbol;

int temp = input.read();

if (temp == -1)

temp = 0;

return temp;

int bit = static_cast<int>(low >> (numStateBits - 1));

output.write(bit);

// Write out the saved underflow bits

for (; numUnderflow > 0; numUnderflow--)

output.write(bit ^ 1);

if (numUnderflow == std::numeric_limits<decltype(numUnderflow)>::max())

throw std::overflow_error("Maximum underflow reached");

numUnderflow++;