mem-cache: Create CPack compressor

Implementation of C-Pack, as described in "C-Pack: A High-
Performance Microprocessor Cache Compression Algorithm".

C-Pack uses pattern matching schemes to detect and compress
frequently appearing data patterns. As in the original paper,
it divides the input in 32-bit words, and uses 6 patterns to
match with its dictionary.

For the patterns, each letter represents a byte: Z is a null
byte, M is a dictionary match, X is a new value. The patterns
are ZZZZ, XXXX, MMMM, MMXX, ZZZX, MMMX.

Change-Id: I2efc9db2c862620dcc1155300e39be558f9017e0
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/11105
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

4 files changed, 784 insertions, 0 deletions

diff --git a/src/mem/cache/compressors/Compressors.py b/src/mem/cache/compressors/Compressors.py
index 1d9de1980..b266ccc95 100644
--- a/src/mem/cache/compressors/Compressors.py
+++ b/src/mem/cache/compressors/Compressors.py
@@ -45,3 +45,8 @@ class BDI(BaseCacheCompressor):
     use_more_compressors = Param.Bool(True, "True if should use all possible" \
         "combinations of base and delta for the compressors. False if using" \
         "only the lowest possible delta size for each base size.");
+
+class CPack(BaseCacheCompressor):
+    type = 'CPack'
+    cxx_class = 'CPack'
+    cxx_header = "mem/cache/compressors/cpack.hh"
diff --git a/src/mem/cache/compressors/SConscript b/src/mem/cache/compressors/SConscript
index 38ce34082..0b3ba6451 100644
--- a/src/mem/cache/compressors/SConscript
+++ b/src/mem/cache/compressors/SConscript
@@ -34,3 +34,4 @@ SimObject('Compressors.py')
 
 Source('base.cc')
 Source('bdi.cc')
+Source('cpack.cc')
diff --git a/src/mem/cache/compressors/cpack.cc b/src/mem/cache/compressors/cpack.cc
new file mode 100644
index 000000000..1192963e2
--- /dev/null
+++ b/src/mem/cache/compressors/cpack.cc
@@ -0,0 +1,227 @@
+/*
+ * Copyright (c) 2018 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.
+ *
+ * Authors: Daniel Carvalho
+ */
+
+/** @file
+ * Implementation of the CPack cache compressor.
+ */
+
+#include "mem/cache/compressors/cpack.hh"
+
+#include <algorithm>
+#include <cstdint>
+
+#include "debug/CacheComp.hh"
+#include "params/CPack.hh"
+
+CPack::CompData::CompData(const std::size_t dictionary_size)
+    : CompressionData()
+{
+}
+
+CPack::CompData::~CompData()
+{
+}
+
+CPack::CPack(const Params *p)
+    : BaseCacheCompressor(p), dictionarySize(2*blkSize/8)
+{
+    dictionary.resize(dictionarySize);
+
+    resetDictionary();
+}
+
+void
+CPack::resetDictionary()
+{
+    // Reset number of valid entries
+    numEntries = 0;
+
+    // Set all entries as 0
+    std::array<uint8_t, 4> zero_word = {0, 0, 0, 0};
+    std::fill(dictionary.begin(), dictionary.end(), zero_word);
+}
+
+std::unique_ptr<CPack::Pattern>
+CPack::compressWord(const uint32_t data)
+{
+    // Split data in bytes
+    const std::array<uint8_t, 4> bytes = {
+        static_cast<uint8_t>(data & 0xFF),
+        static_cast<uint8_t>((data >> 8) & 0xFF),
+        static_cast<uint8_t>((data >> 16) & 0xFF),
+        static_cast<uint8_t>((data >> 24) & 0xFF)
+    };
+
+    // Start as a no-match pattern. A negative match location is used so that
+    // patterns that depend on the dictionary entry don't match
+    std::unique_ptr<Pattern> pattern =
+        PatternFactory::getPattern(bytes, {0, 0, 0, 0}, -1);
+
+    // Search for word on dictionary
+    for (std::size_t i = 0; i < numEntries; i++) {
+        // Try matching input with possible patterns
+        std::unique_ptr<Pattern> temp_pattern =
+            PatternFactory::getPattern(bytes, dictionary[i], i);
+
+        // Check if found pattern is better than previous
+        if (temp_pattern->getSizeBits() < pattern->getSizeBits()) {
+            pattern = std::move(temp_pattern);
+        }
+    }
+
+    // Update stats
+    patternStats[pattern->getPatternNumber()]++;
+
+    // Push into dictionary
+    if ((numEntries < dictionarySize) && pattern->shouldAllocate()) {
+        dictionary[numEntries++] = bytes;
+    }
+
+    return pattern;
+}
+
+std::unique_ptr<BaseCacheCompressor::CompressionData>
+CPack::compress(const uint64_t* data, Cycles& comp_lat, Cycles& decomp_lat)
+{
+    std::unique_ptr<CompData> comp_data =
+        std::unique_ptr<CompData>(new CompData(dictionarySize));
+
+    // Compression size
+    std::size_t size = 0;
+
+    // Reset dictionary
+    resetDictionary();
+
+    // Compress every word sequentially
+    for (std::size_t i = 0; i < blkSize/8; i++) {
+        const uint32_t first_word = ((data[i])&0xFFFFFFFF00000000) >> 32;
+        const uint32_t second_word = (data[i])&0x00000000FFFFFFFF;
+
+        // Compress both words
+        std::unique_ptr<Pattern> first_pattern = compressWord(first_word);
+        std::unique_ptr<Pattern> second_pattern = compressWord(second_word);
+
+        // Update total line compression size
+        size += first_pattern->getSizeBits() + second_pattern->getSizeBits();
+
+        // Print debug information
+        DPRINTF(CacheComp, "Compressed %08x to %s\n", first_word,
+                first_pattern->print());
+        DPRINTF(CacheComp, "Compressed %08x to %s\n", second_word,
+                second_pattern->print());
+
+        // Append to pattern list
+        comp_data->entries.push_back(std::move(first_pattern));
+        comp_data->entries.push_back(std::move(second_pattern));
+    }
+
+    // Set final compression size
+    comp_data->setSizeBits(size);
+
+    // Set compression latency (Accounts for pattern matching, length
+    // generation, packaging and shifting)
+    comp_lat = Cycles(blkSize/8+5);
+
+    // Set decompression latency (1 qword per cycle)
+    decomp_lat = Cycles(blkSize/8);
+
+    // Return compressed line
+    return std::move(comp_data);
+}
+
+uint32_t
+CPack::decompressWord(const Pattern* pattern)
+{
+    std::array<uint8_t, 4> data;
+
+    // Search for matching entry
+    std::vector<std::array<uint8_t, 4>>::iterator entry_it =
+        dictionary.begin();
+    std::advance(entry_it, pattern->getMatchLocation());
+
+    // Decompress the match. If the decompressed value must be added to
+    // the dictionary, do it
+    if (pattern->decompress(*entry_it, data)) {
+        dictionary[numEntries++] = data;
+    }
+
+    // Return word
+    return (((((data[3] << 8) | data[2]) << 8) | data[1]) << 8) | data[0];
+}
+
+void
+CPack::decompress(const CompressionData* comp_data, uint64_t* data)
+{
+    const CompData* cpack_comp_data = static_cast<const CompData*>(comp_data);
+
+    // Reset dictionary
+    resetDictionary();
+
+    // Decompress every entry sequentially
+    std::vector<uint32_t> decomp_words;
+    for (const auto& entry : cpack_comp_data->entries) {
+        const uint32_t word = decompressWord(&*entry);
+        decomp_words.push_back(word);
+
+        // Print debug information
+        DPRINTF(CacheComp, "Decompressed %s to %x\n", entry->print(), word);
+    }
+
+    // Concatenate the decompressed words to generate the cache lines
+    for (std::size_t i = 0; i < blkSize/8; i++) {
+        data[i] = (static_cast<uint64_t>(decomp_words[2*i]) << 32) |
+                        decomp_words[2*i+1];
+    }
+}
+
+void
+CPack::regStats()
+{
+    BaseCacheCompressor::regStats();
+
+    // We store the frequency of each pattern
+    patternStats
+        .init(Pattern::getNumPatterns())
+        .name(name() + ".pattern")
+        .desc("Number of data entries that were compressed to this pattern.")
+        ;
+
+    for (unsigned i = 0; i < Pattern::getNumPatterns(); ++i) {
+        patternStats.subname(i, Pattern::getName(i));
+        patternStats.subdesc(i, "Number of data entries that match pattern " +
+                                Pattern::getName(i));
+    }
+}
+
+CPack*
+CPackParams::create()
+{
+    return new CPack(this);
+}
diff --git a/src/mem/cache/compressors/cpack.hh b/src/mem/cache/compressors/cpack.hh
new file mode 100644
index 000000000..664a37601
--- /dev/null
+++ b/src/mem/cache/compressors/cpack.hh
@@ -0,0 +1,551 @@
+/*
+ * Copyright (c) 2018 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.
+ *
+ * Authors: Daniel Carvalho
+ */
+
+/** @file
+ * Definition of CPack compression, from "C-Pack: A High-Performance
+ * Microprocessor Cache Compression Algorithm".
+ *
+ * The dictionary is composed of 32-bit entries.
+ *
+ * The patterns are implemented as individual classes that have a checking
+ * function isPattern(), to determine if the data fits the pattern, and a
+ * decompress() function, which decompresses the contents of a pattern.
+ * Every new pattern must inherit from the Pattern class and be added to the
+ * patternFactory.
+ */
+
+#ifndef __MEM_CACHE_COMPRESSORS_CPACK_HH__
+#define __MEM_CACHE_COMPRESSORS_CPACK_HH__
+
+#include <array>
+#include <cstdint>
+#include <map>
+#include <memory>
+#include <vector>
+
+#include "base/types.hh"
+#include "mem/cache/compressors/base.hh"
+
+struct CPackParams;
+
+class CPack : public BaseCacheCompressor
+{
+  private:
+    /**
+     * Compression data for CPack. It consists of a vector of patterns.
+     */
+    class CompData;
+
+    // Forward declaration of all possible patterns
+    class Pattern;
+    class PatternZZZZ;
+    class PatternXXXX;
+    class PatternMMMM;
+    class PatternMMXX;
+    class PatternZZZX;
+    class PatternMMMX;
+
+    /**
+     * Create a factory to determine if input matches a pattern. The if else
+     * chains are constructed by recursion. The patterns should be explored
+     * sorted by size for correct behaviour.
+     */
+    template <class Head, class... Tail>
+    struct Factory
+    {
+        static std::unique_ptr<Pattern> getPattern(
+            const std::array<uint8_t, 4>& bytes,
+            const std::array<uint8_t, 4>& dict_bytes, const int match_location)
+        {
+            // If match this pattern, instantiate it. If a negative match
+            // location is used, the patterns that use the dictionary bytes
+            // must return false. This is used when there are no dictionary
+            // entries yet
+            if (Head::isPattern(bytes, dict_bytes, match_location)) {
+                return std::unique_ptr<Pattern>(
+                            new Head(bytes, match_location));
+            // Otherwise, go for next pattern
+            } else {
+                return Factory<Tail...>::getPattern(bytes, dict_bytes,
+                                                    match_location);
+            }
+        }
+    };
+
+    /**
+     * Specialization to end the recursion.
+     */
+    template <class Head>
+    struct Factory<Head>
+    {
+        static std::unique_ptr<Pattern> getPattern(
+            const std::array<uint8_t, 4>& bytes,
+            const std::array<uint8_t, 4>& dict_bytes, const int match_location)
+        {
+            // Instantiate last pattern. Should be the XXXX pattern.
+            return std::unique_ptr<Pattern>(new Head(bytes, match_location));
+        }
+    };
+
+    /**
+     * Convenience factory declaration. The templates must be organized by
+     * size, with the smallest first, and "no-match" last.
+     */
+    using PatternFactory = Factory<PatternZZZZ, PatternMMMM, PatternZZZX,
+                                   PatternMMMX, PatternMMXX, PatternXXXX>;
+
+    /**
+     * The dictionary.
+     */
+    std::vector<std::array<uint8_t, 4>> dictionary;
+
+    /**
+     * Dictionary size.
+     */
+    const std::size_t dictionarySize;
+
+    /**
+     * Number of valid entries in the dictionary.
+     */
+    std::size_t numEntries;
+
+    /**
+     * @defgroup CompressionStats Compression specific statistics.
+     * @{
+     */
+
+    /**
+     * Number of data entries that were compressed to each pattern.
+     */
+    Stats::Vector patternStats;
+
+    /**
+     * @}
+     */
+
+    /**
+     * Compress data.
+     *
+     * @param data Data to be compressed.
+     * @return The pattern this data matches.
+     */
+    std::unique_ptr<Pattern> compressWord(const uint32_t data);
+
+    /**
+     * Decompress a word.
+     *
+     * @param pattern The pattern to be decompressed.
+     * @return The decompressed word.
+     */
+    uint32_t decompressWord(const Pattern* pattern);
+
+    /**
+     * Clear all dictionary entries.
+     */
+    void resetDictionary();
+
+    /**
+     * Apply compression.
+     *
+     * @param data The cache line to be compressed.
+     * @param comp_lat Compression latency in number of cycles.
+     * @param decomp_lat Decompression latency in number of cycles.
+     * @return Cache line after compression.
+     */
+    std::unique_ptr<BaseCacheCompressor::CompressionData> compress(
+        const uint64_t* data, Cycles& comp_lat, Cycles& decomp_lat) override;
+
+    /**
+     * Decompress data.
+     *
+     * @param comp_data Compressed cache line.
+     * @param data The cache line to be decompressed.
+     */
+    void decompress(const CompressionData* comp_data, uint64_t* data) override;
+
+  public:
+    /** Convenience typedef. */
+     typedef CPackParams Params;
+
+    /**
+     * Default constructor.
+     */
+    CPack(const Params *p);
+
+    /**
+     * Default destructor.
+     */
+    ~CPack() {};
+
+    /**
+     * Register local statistics.
+     */
+    void regStats() override;
+};
+
+/**
+ * The compressed data is composed of multiple pattern entries. To add a new
+ * pattern one should inherit from this class and implement isPattern() and
+ * decompress. Then the new pattern must be added to the PatternFactory
+ * declaration in crescent order of size (in the CPack class). The pattern
+ * must be also added to the Name enum in the CPack::Pattern class before
+ * NUM_PATTERNS.
+ */
+class CPack::Pattern
+{
+  protected:
+
+    /**
+     * The patterns proposed in the paper. Each letter represents a byte:
+     * Z is a null byte, M is a dictionary match, X is a new value.
+     * These are used as indexes to reference the pattern data. If a new
+     * pattern is added, it must be done before NUM_PATTERNS.
+     */
+    typedef enum {
+        ZZZZ, XXXX, MMMM, MMXX, ZZZX, MMMX, NUM_PATTERNS
+    } PatternNumber;
+
+    /**
+     * Pattern enum number.
+     */
+    const PatternNumber patternNumber;
+
+    /**
+     * Code associated to the pattern.
+     */
+    const uint8_t code;
+
+    /**
+     * Length, in bits, of the code and match location.
+     */
+    const uint8_t length;
+
+    /**
+     * Number of unmatched bytes;
+     */
+    const uint8_t numUnmatchedBytes;
+
+    /**
+     * Index representing the the match location.
+     */
+    const int matchLocation;
+
+    /**
+     * Wether the pattern allocates a dictionary entry or not.
+     */
+    const bool allocate;
+
+    /**
+     * Get code of this pattern.
+     *
+     * @return The code.
+     */
+    uint8_t getCode() const { return code; }
+
+  public:
+    /**
+     * Default constructor.
+     *
+     * @param number Pattern number.
+     * @param code Code associated to this pattern.
+     * @param metadata_length Length, in bits, of the code and match location.
+     * @param num_unmatched_bytes Number of unmatched bytes.
+     * @param match_location Index of the match location.
+     */
+    Pattern(const PatternNumber number, const uint64_t code,
+            const uint64_t metadata_length, const uint64_t num_unmatched_bytes,
+            const int match_location, const bool allocate = true)
+        : patternNumber(number), code(code), length(metadata_length),
+          numUnmatchedBytes(num_unmatched_bytes),
+          matchLocation(match_location), allocate(allocate) {};
+
+    /**
+     * Default destructor.
+     */
+    virtual ~Pattern() = default;
+
+    /**
+     * Trick function to get the number of patterns.
+     *
+     * @return The number of defined patterns.
+     */
+    static uint64_t getNumPatterns() { return NUM_PATTERNS; };
+
+    /**
+     * Get enum number associated to this pattern.
+     *
+     * @return The pattern enum number.
+     */
+    PatternNumber getPatternNumber() const { return patternNumber; };
+
+    /**
+     * Get meta-name assigned to the given pattern.
+     *
+     * @param number The number of the pattern.
+     * @return The meta-name of the pattern.
+     */
+    static std::string getName(int number)
+    {
+        static std::map<PatternNumber, std::string> patternNames = {
+            {ZZZZ, "ZZZZ"}, {XXXX, "XXXX"}, {MMMM, "MMMM"},
+            {MMXX, "MMXX"}, {ZZZX, "ZZZX"}, {MMMX, "MMMX"}
+        };
+
+        return patternNames[(PatternNumber)number];
+    };
+
+    /**
+     * Get the index of the dictionary match location.
+     *
+     * @return The index of the match location.
+     */
+    uint8_t getMatchLocation() const { return matchLocation; }
+
+    /**
+     * Get size, in bits, of the pattern (excluding prefix). Corresponds to
+     * unmatched_data_size + code_length.
+     *
+     * @return The size.
+     */
+    std::size_t getSizeBits() const {
+        return numUnmatchedBytes*CHAR_BIT + length;
+    }
+
+    /**
+     * Determine if pattern allocates a dictionary entry.
+     *
+     * @return True if should allocate a dictionary entry.
+     */
+    bool shouldAllocate() const {
+        return allocate;
+    }
+
+    std::string print() const {
+        return csprintf("pattern %s (encoding %x, size %u bits)",
+                        getName(patternNumber), getCode(), getSizeBits());
+    }
+
+    /**
+     * Decompress the pattern. Each pattern has its own way of interpreting
+     * its data.
+     *
+     * @param dict_bytes The bytes in the corresponding matching entry.
+     * @param data The decompressed pattern.
+     * @return Whether entry should be added to dictionary or not.
+     */
+    virtual bool decompress(const std::array<uint8_t, 4> dict_bytes,
+                            std::array<uint8_t, 4>& data) const = 0;
+};
+
+class CPack::PatternZZZZ : public Pattern
+{
+  public:
+    PatternZZZZ(const std::array<uint8_t, 4> bytes, const int match_location)
+        : Pattern(ZZZZ, 0x0, 2, 0, 0, false) {}
+
+    static bool isPattern(const std::array<uint8_t, 4>& bytes,
+                          const std::array<uint8_t, 4>& dict_bytes,
+                          const int match_location)
+    {
+        return (bytes[3] == 0) && (bytes[2] == 0) && (bytes[1] == 0) &&
+               (bytes[0] == 0);
+    }
+
+    bool decompress(const std::array<uint8_t, 4> dict_bytes,
+                    std::array<uint8_t, 4>& data) const override
+    {
+        data = {0, 0, 0, 0};
+        return false;
+    }
+};
+
+class CPack::PatternXXXX : public Pattern
+{
+  private:
+    /**
+     * A copy of the word.
+     */
+    const std::array<uint8_t, 4> bytes;
+
+  public:
+    PatternXXXX(const std::array<uint8_t, 4> bytes, const int match_location)
+        : Pattern(XXXX, 0x1, 2, 4, 0, true), bytes(bytes) {}
+
+    static bool isPattern(const std::array<uint8_t, 4>& bytes,
+                          const std::array<uint8_t, 4>& dict_bytes,
+                          const int match_location)
+    {
+        // It can always be an unmatch, as it is set to this class when other
+        // patterns fail
+        return true;
+    }
+
+    bool decompress(const std::array<uint8_t, 4> dict_bytes,
+                    std::array<uint8_t, 4>& data) const override
+    {
+        data = bytes;
+        return true;
+    }
+};
+
+class CPack::PatternMMMM : public Pattern
+{
+  public:
+    PatternMMMM(const std::array<uint8_t, 4> bytes, const int match_location)
+        : Pattern(MMMM, 0x2, 6, 0, match_location, true) {}
+
+    static bool isPattern(const std::array<uint8_t, 4>& bytes,
+                          const std::array<uint8_t, 4>& dict_bytes,
+                          const int match_location)
+    {
+        return (bytes == dict_bytes) && (match_location >= 0);
+    }
+
+    bool decompress(const std::array<uint8_t, 4> dict_bytes,
+                    std::array<uint8_t, 4>& data) const override
+    {
+        data = dict_bytes;
+        return true;
+    }
+};
+
+class CPack::PatternMMXX : public Pattern
+{
+  private:
+    /**
+     * A copy of the unmatched bytes.
+     */
+    const uint8_t byte0;
+    const uint8_t byte1;
+
+  public:
+    PatternMMXX(const std::array<uint8_t, 4> bytes, const int match_location)
+        : Pattern(MMXX, 0xC, 8, 2, match_location, true),
+                  byte0(bytes[0]), byte1(bytes[1]) {}
+
+    static bool isPattern(const std::array<uint8_t, 4>& bytes,
+                          const std::array<uint8_t, 4>& dict_bytes,
+                          const int match_location)
+    {
+        // Notice we don't compare bytes[0], as otherwise we'd be unnecessarily
+        // discarding MMXM. If that pattern is added this should be modified
+        return (bytes[3] == dict_bytes[3]) && (bytes[2] == dict_bytes[2]) &&
+               (bytes[1] != dict_bytes[1]) && (match_location >= 0);
+
+    }
+
+    bool decompress(const std::array<uint8_t, 4> dict_bytes,
+                    std::array<uint8_t, 4>& data) const override
+    {
+        data = {byte0, byte1, dict_bytes[2], dict_bytes[3]};
+        return true;
+    }
+};
+
+class CPack::PatternZZZX : public Pattern
+{
+  private:
+    /**
+     * A copy of the unmatched byte.
+     */
+    const uint8_t byte;
+
+  public:
+    PatternZZZX(const std::array<uint8_t, 4> bytes, const int match_location)
+        : Pattern(ZZZX, 0xD, 4, 1, 0, false), byte(bytes[0]) {}
+
+    static bool isPattern(const std::array<uint8_t, 4>& bytes,
+                          const std::array<uint8_t, 4>& dict_bytes,
+                          const int match_location)
+    {
+        return (bytes[3] == 0) && (bytes[2] == 0) && (bytes[1] == 0) &&
+               (bytes[0] != 0);
+    }
+
+    bool decompress(const std::array<uint8_t, 4> dict_bytes,
+                    std::array<uint8_t, 4>& data) const override
+    {
+        data = {byte, 0, 0, 0};
+        return false;
+    }
+};
+
+class CPack::PatternMMMX : public Pattern
+{
+  private:
+    /**
+     * A copy of the unmatched byte.
+     */
+    const uint8_t byte;
+
+  public:
+    PatternMMMX(const std::array<uint8_t, 4> bytes, const int match_location)
+        : Pattern(MMMX, 0xE, 8, 1, match_location, true),
+                  byte(bytes[0]) {}
+
+    static bool isPattern(const std::array<uint8_t, 4>& bytes,
+                          const std::array<uint8_t, 4>& dict_bytes,
+                          const int match_location)
+    {
+        return (bytes[3] == dict_bytes[3]) && (bytes[2] == dict_bytes[2]) &&
+               (bytes[1] == dict_bytes[1]) && (bytes[0] != dict_bytes[0]) &&
+               (match_location >= 0);
+    }
+
+    bool decompress(const std::array<uint8_t, 4> dict_bytes,
+                    std::array<uint8_t, 4>& data) const override
+    {
+        data = {byte, dict_bytes[1], dict_bytes[2], dict_bytes[3]};
+        return true;
+    }
+};
+
+class CPack::CompData : public CompressionData
+{
+  public:
+    /**
+     * The patterns matched in the original line.
+     */
+    std::vector<std::unique_ptr<Pattern>> entries;
+
+    /**
+     * Default constructor.
+     *
+     * @param dictionary_size Number of entries in the dictionary.
+     */
+    CompData(const std::size_t dictionary_size);
+
+    /**
+     * Default destructor.
+     */
+    ~CompData();
+};
+
+#endif //__MEM_CACHE_COMPRESSORS_CPACK_HH__