src/mem/cache/compressors/fpcd.cc

   1 /*
   2  * Copyright (c) 2019 Inria
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met: redistributions of source code must retain the above copyright
   8  * notice, this list of conditions and the following disclaimer;
   9  * redistributions in binary form must reproduce the above copyright
  10  * notice, this list of conditions and the following disclaimer in the
  11  * documentation and/or other materials provided with the distribution;
  12  * neither the name of the copyright holders nor the names of its
  13  * contributors may be used to endorse or promote products derived from
  14  * this software without specific prior written permission.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  17  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  18  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  19  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  20  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  21  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  22  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  26  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  *
  28  * Authors: Daniel Carvalho
  29  */
  30
  31 /** @file
  32  * Implementation of the FPC-D cache compressor.
  33  */
  34
  35 #include "mem/cache/compressors/fpcd.hh"
  36
  37 #include "mem/cache/compressors/dictionary_compressor_impl.hh"
  38 #include "params/FPCD.hh"
  39
  40 FPCD::FPCD(const Params *p)
  41     : DictionaryCompressor<uint32_t>(p)
  42 {
  43 }
  44
  45 void
  46 FPCD::addToDictionary(DictionaryEntry data)
  47 {
  48     // The dictionary behaves as a table with FIFO as replacement policy
  49     if (numEntries == 2) {
  50         dictionary[penultimateIndex] = dictionary[previousIndex];
  51         dictionary[previousIndex] = data;
  52     } else {
  53         dictionary[numEntries++] = data;
  54     }
  55 }
  56
  57 std::unique_ptr<BaseCacheCompressor::CompressionData>
  58 FPCD::compress(const uint64_t* data, Cycles& comp_lat, Cycles& decomp_lat)
  59 {
  60     std::unique_ptr<BaseCacheCompressor::CompressionData> comp_data =
  61         DictionaryCompressor<uint32_t>::compress(data);
  62
  63     // Set compression latency (Accounts for zero checks, ones check, match
  64     // previous check, match penultimate check, repeated values check, pattern
  65     // selection, shifting, at a rate of 16B per cycle)
  66     comp_lat = Cycles(blkSize/2);
  67
  68     // Set decompression latency. The original claim of 2 cycles is likely
  69     // too unrealistic
  70     decomp_lat = Cycles(4);
  71
  72     // Return compressed line
  73     return comp_data;
  74 }
  75
  76 FPCD*
  77 FPCDParams::create()
  78 {
  79     return new FPCD(this);
  80 }