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/*
* Copyright (c) 2019-2020 Inria
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/** @file
* Definition of the a multi compressor that choses the best compression
* among multiple compressors.
*/
#ifndef __MEM_CACHE_COMPRESSORS_MULTI_HH__
#define __MEM_CACHE_COMPRESSORS_MULTI_HH__
#include <cstdint>
#include <vector>
#include "base/statistics.hh"
#include "base/types.hh"
#include "mem/cache/compressors/base.hh"
namespace gem5
{
struct MultiCompressorParams;
namespace compression
{
class Multi : public Base
{
protected:
/**
* Compression data for the multi compressor. It contains the compression
* data of the best compressor, along with its index in the list of
* sub-compressors.
*/
class MultiCompData;
/** List of sub-compressors. */
std::vector<Base*> compressors;
/**
* An encoding is associated to each sub-compressor to inform which
* sub-compressor to use when decompressing data. This information can
* be added either to the tag entry, in which case no extra bits are
* added to the compressed data (numEncodingBits = 0), or to the
* compressed data itself.
*
* There is no encoding reserved for the uncompressed case; it is assumed
* that an "is compressed" bit is stored in the tags. Therefore, even if
* storing the encoding within the compressed data, these extra bits are
* not added when the data is uncompressible.
*
* These extra bits are taken into account when thresholding the
* compressed data's size.
*/
const std::size_t numEncodingBits;
/**
* Extra decompression latency to be added to the sub-compressor's
* decompression latency. This can different from zero due to decoding,
* shifting, or packaging, for example.
*/
const Cycles extraDecompressionLatency;
struct MultiStats : public statistics::Group
{
const Multi& compressor;
MultiStats(BaseStats &base_group, Multi& _compressor);
void regStats() override;
/**
* Number of times each compressor provided the nth best compression.
*/
statistics::Vector2d ranks;
} multiStats;
public:
typedef MultiCompressorParams Params;
Multi(const Params &p);
~Multi();
void setCache(BaseCache *_cache) override;
std::unique_ptr<Base::CompressionData> compress(
const std::vector<Base::Chunk>& chunks,
Cycles& comp_lat, Cycles& decomp_lat) override;
void decompress(const CompressionData* comp_data, uint64_t* data) override;
};
class Multi::MultiCompData : public CompressionData
{
private:
/** Index of the compressor that provided these compression results. */
const uint8_t index;
public:
/** Compression data of the best compressor. */
std::unique_ptr<Base::CompressionData> compData;
/**
* Default constructor.
*
* @param index Index of the compressor that provided this compression.
* @param comp_data Compression data of the best compressor.
*/
MultiCompData(unsigned index,
std::unique_ptr<Base::CompressionData> comp_data);
/** Default destructor. */
~MultiCompData() = default;
/** Get the index of the best compressor. */
uint8_t getIndex() const;
};
} // namespace compression
} // namespace gem5
#endif //__MEM_CACHE_COMPRESSORS_MULTI_HH__