AbstractPrefixCodeDecoder.h

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/*
    RawSpeed - RAW file decoder.
 
    Copyright (C) 2017 Axel Waggershauser
    Copyright (C) 2017-2018 Roman Lebedev
 
    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.
 
    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.
 
    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
 
#pragma once
 
#include "rawspeedconfig.h"
#include "adt/Invariant.h"
#include "codes/AbstractPrefixCodeTranscoder.h"
#include <cstdint>
 
namespace rawspeed {
 
template <typename CodeTag>
class AbstractPrefixCodeDecoder : public AbstractPrefixCodeTranscoder<CodeTag> {
public:
  using Base = AbstractPrefixCodeTranscoder<CodeTag>;
 
  using Tag = typename Base::Tag;
  using Parent = typename Base::Parent;
  using CodeSymbol = typename Base::CodeSymbol;
  using Traits = typename Base::Traits;
 
  using Base::Base;
 
  template <typename BIT_STREAM, bool FULL_DECODE>
  int processSymbol(BIT_STREAM& bs, CodeSymbol symbol,
                    typename Traits::CodeValueTy codeValue) const {
    invariant(symbol.code_len >= 0 &&
              symbol.code_len <= Traits::MaxCodeLenghtBits);
 
    // If we were only looking for symbol's code value, then just return it.
    if constexpr (!FULL_DECODE)
      return codeValue;
 
    // Else, treat it as the length of following difference
    // that we need to read and extend.
    int diff_l = codeValue;
    invariant(diff_l >= 0 && diff_l <= 16);
 
    if (diff_l == 16) {
      if (Base::handleDNGBug16())
        bs.skipBitsNoFill(16);
      return -32768;
    }
 
    invariant(symbol.code_len + diff_l <= 32);
    return diff_l ? extend(bs.getBitsNoFill(diff_l), diff_l) : 0;
  }
 
  // Figure F.12 – Extending the sign bit of a decoded value in V
  // WARNING: this is *not* your normal 2's complement sign extension!
  static int RAWSPEED_READNONE extend(uint32_t diff, uint32_t len) {
    invariant(len > 0);
    auto ret = static_cast<int32_t>(diff);
    if ((diff & (1 << (len - 1))) == 0)
      ret -= (1 << len) - 1;
    return ret;
  }
};
 
} // namespace rawspeed