/*
 * Copyright 2011-2019, European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "CACDecoder.h"

void COMP::CACDecoder::UpdateInterval()
{
	COMP_TRYTHIS_SPEED
	unsigned int nbBit = 0U;
	do
	{
		m_Range += m_Range;
		nbBit++;
	} while (m_Range <= c_FirstQtr);
	m_Value <<= nbBit;
	m_Value += InputBits(nbBit);
	COMP_CATCHTHIS_SPEED
}

unsigned int COMP::CACDecoder::DecodeSymbol(
	CACModel &i_Mod // the multi-symbols probability model
)
{
	COMP_TRYTHIS_SPEED
	unsigned int index = 1U;
	const unsigned __int32 r = m_Range / i_Mod.GetCumFreq(0);
	unsigned __int32 rLps = i_Mod.GetCumFreq(index) * r;
	while (rLps > m_Value)
		rLps = i_Mod.GetCumFreq(++index) * r;
	const unsigned int symbol = i_Mod.GetSymbol(index);
	m_Value -= rLps;
	if (index == 1U)
	{
		m_Range -= rLps;
		i_Mod.UpdateMps();
	}
	else
	{
		m_Range = i_Mod.GetFreq(index) * r;
		i_Mod.UpdateLps(index);
	}
	if (m_Range <= c_FirstQtr)
		UpdateInterval();
	return symbol;
	COMP_CATCHTHIS_SPEED
}