src/mem/cache/compressors/fpcd.cc

/*
 * Copyright (c) 2019 Inria
 * All rights reserved.
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 * modification, are permitted provided that the following conditions are
 * met: redistributions of source code must retain the above copyright
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 * redistributions in binary form must reproduce the above copyright
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 * 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
 * Implementation of the FPC-D cache compressor.
 */

#include "mem/cache/compressors/fpcd.hh"

#include "mem/cache/compressors/dictionary_compressor_impl.hh"
#include "params/FPCD.hh"

FPCD::FPCD(const Params *p)
    : DictionaryCompressor<uint32_t>(p)
{
}

void
FPCD::addToDictionary(DictionaryEntry data)
{
    // The dictionary behaves as a table with FIFO as replacement policy
    if (numEntries == 2) {
        dictionary[penultimateIndex] = dictionary[previousIndex];
        dictionary[previousIndex] = data;
    } else {
        dictionary[numEntries++] = data;
    }
}

std::unique_ptr<BaseCacheCompressor::CompressionData>
FPCD::compress(const uint64_t* data, Cycles& comp_lat, Cycles& decomp_lat)
{
    std::unique_ptr<BaseCacheCompressor::CompressionData> comp_data =
        DictionaryCompressor<uint32_t>::compress(data);

    // Set compression latency (Accounts for zero checks, ones check, match
    // previous check, match penultimate check, repeated values check, pattern
    // selection, shifting, at a rate of 16B per cycle)
    comp_lat = Cycles(blkSize/2);

    // Set decompression latency. The original claim of 2 cycles is likely
    // too unrealistic
    decomp_lat = Cycles(4);

    // Return compressed line
    return comp_data;
}

FPCD*
FPCDParams::create()
{
    return new FPCD(this);
}