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https://github.com/SatDump/SatDump
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60 lines
1.5 KiB
C++
60 lines
1.5 KiB
C++
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/*
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* Copyright 2011-2019, European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT)
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "CACDecoder.h"
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void COMP::CACDecoder::UpdateInterval()
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{
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COMP_TRYTHIS_SPEED
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unsigned int nbBit = 0U;
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do
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{
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m_Range += m_Range;
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nbBit++;
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} while (m_Range <= c_FirstQtr);
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m_Value <<= nbBit;
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m_Value += InputBits(nbBit);
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COMP_CATCHTHIS_SPEED
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}
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unsigned int COMP::CACDecoder::DecodeSymbol(
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CACModel &i_Mod // the multi-symbols probability model
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)
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{
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COMP_TRYTHIS_SPEED
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unsigned int index = 1U;
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const unsigned __int32 r = m_Range / i_Mod.GetCumFreq(0);
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unsigned __int32 rLps = i_Mod.GetCumFreq(index) * r;
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while (rLps > m_Value)
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rLps = i_Mod.GetCumFreq(++index) * r;
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const unsigned int symbol = i_Mod.GetSymbol(index);
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m_Value -= rLps;
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if (index == 1U)
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{
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m_Range -= rLps;
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i_Mod.UpdateMps();
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}
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else
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{
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m_Range = i_Mod.GetFreq(index) * r;
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i_Mod.UpdateLps(index);
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}
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if (m_Range <= c_FirstQtr)
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UpdateInterval();
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return symbol;
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COMP_CATCHTHIS_SPEED
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}
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