src/mem/cache/compressors/perfect.hh

/*
 * Copyright (c) 2019 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
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Authors: Daniel Carvalho
 */

/** @file
 * Definition of a perfect compressor, that always manages to compress to
 * its maximum compression ratio.
 */

#ifndef __MEM_CACHE_COMPRESSORS_PERFECT_COMPRESSOR_HH__
#define __MEM_CACHE_COMPRESSORS_PERFECT_COMPRESSOR_HH__

#include <cstdint>
#include <memory>
#include <vector>

#include "base/types.hh"
#include "mem/cache/compressors/base.hh"

struct PerfectCompressorParams;

class PerfectCompressor : public BaseCacheCompressor
{
  protected:
    class CompData;

    /** Size to which this compressor always compresses. */
    const int compressedSize;

    /** Number of cycles needed to perform compression. */
    const Cycles compressionLatency;

    /** Number of cycles needed to perform decompression. */
    const Cycles decompressionLatency;

    std::unique_ptr<CompressionData> compress(const uint64_t* cache_line,
        Cycles& comp_lat, Cycles& decomp_lat) override;

    void decompress(const CompressionData* comp_data, uint64_t* data) override;

  public:
    typedef PerfectCompressorParams Params;
    PerfectCompressor(const Params *p);
    ~PerfectCompressor() {};
};

class PerfectCompressor::CompData : public CompressionData
{
  public:
    /** The original data is simply copied over to this vector. */
    std::vector<uint64_t> entries;

    /**
     * Default constructor that creates a copy of the original data.
     *
     * @param data The data to be compressed.
     * @param num_entries The number of qwords in the data.
     */
    CompData(const uint64_t* data, std::size_t num_entries);
    ~CompData() = default;
};

#endif //__MEM_CACHE_COMPRESSORS_PERFECT_COMPRESSOR_HH__