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28 * Authors: Daniel Carvalho
32 * Definition of a dictionary based cache compressor. Each entry is compared
33 * against a dictionary to search for matches.
35 * The dictionary is composed of 32-bit entries, and the comparison is done
38 * The patterns are implemented as individual classes that have a checking
39 * function isPattern(), to determine if the data fits the pattern, and a
40 * decompress() function, which decompresses the contents of a pattern.
41 * Every new pattern must inherit from the Pattern class and be added to the
45 #ifndef __MEM_CACHE_COMPRESSORS_DICTIONARY_COMPRESSOR_HH__
46 #define __MEM_CACHE_COMPRESSORS_DICTIONARY_COMPRESSOR_HH__
53 #include <type_traits>
56 #include "base/types.hh"
57 #include "mem/cache/compressors/base.hh"
59 struct BaseDictionaryCompressorParams;
61 class BaseDictionaryCompressor : public BaseCacheCompressor
64 /** Dictionary size. */
65 const std::size_t dictionarySize;
67 /** Number of valid entries in the dictionary. */
68 std::size_t numEntries;
71 * @defgroup CompressionStats Compression specific statistics.
75 /** Number of data entries that were compressed to each pattern. */
76 Stats::Vector patternStats;
83 * Trick function to get the number of patterns.
85 * @return The number of defined patterns.
87 virtual uint64_t getNumPatterns() const = 0;
90 * Get meta-name assigned to the given pattern.
92 * @param number The number of the pattern.
93 * @return The meta-name of the pattern.
95 virtual std::string getName(int number) const = 0;
98 typedef BaseDictionaryCompressorParams Params;
99 BaseDictionaryCompressor(const Params *p);
100 ~BaseDictionaryCompressor() = default;
102 void regStats() override;
106 * A template version of the dictionary compressor that allows to choose the
109 * @tparam The type of a dictionary entry (e.g., uint16_t, uint32_t, etc).
112 class DictionaryCompressor : public BaseDictionaryCompressor
115 /** Convenience typedef for a dictionary entry. */
116 typedef std::array<uint8_t, sizeof(T)> DictionaryEntry;
119 * Compression data for the dictionary compressor. It consists of a vector
124 // Forward declaration of a pattern
126 class UncompressedPattern;
129 template <T value, T mask>
130 class MaskedValuePattern;
131 template <T mask, int location>
132 class LocatedMaskedPattern;
133 template <class RepT>
134 class RepeatedValuePattern;
135 template <std::size_t DeltaSizeBits>
139 * Create a factory to determine if input matches a pattern. The if else
140 * chains are constructed by recursion. The patterns should be explored
141 * sorted by size for correct behaviour.
143 template <class Head, class... Tail>
146 static std::unique_ptr<Pattern> getPattern(
147 const DictionaryEntry& bytes, const DictionaryEntry& dict_bytes,
148 const int match_location)
150 // If match this pattern, instantiate it. If a negative match
151 // location is used, the patterns that use the dictionary bytes
152 // must return false. This is used when there are no dictionary
154 if (Head::isPattern(bytes, dict_bytes, match_location)) {
155 return std::unique_ptr<Pattern>(
156 new Head(bytes, match_location));
157 // Otherwise, go for next pattern
159 return Factory<Tail...>::getPattern(bytes, dict_bytes,
166 * Specialization to end the recursion. This must be called when all
167 * other patterns failed, and there is no choice but to leave data
168 * uncompressed. As such, this pattern must inherit from the uncompressed
171 template <class Head>
174 static_assert(std::is_base_of<UncompressedPattern, Head>::value,
175 "The last pattern must always be derived from the uncompressed "
178 static std::unique_ptr<Pattern>
179 getPattern(const DictionaryEntry& bytes,
180 const DictionaryEntry& dict_bytes, const int match_location)
182 return std::unique_ptr<Pattern>(new Head(bytes, match_location));
186 /** The dictionary. */
187 std::vector<DictionaryEntry> dictionary;
190 * Since the factory cannot be instantiated here, classes that inherit
191 * from this base class have to implement the call to their factory's
194 virtual std::unique_ptr<Pattern>
195 getPattern(const DictionaryEntry& bytes, const DictionaryEntry& dict_bytes,
196 const int match_location) const = 0;
201 * @param data Data to be compressed.
202 * @return The pattern this data matches.
204 std::unique_ptr<Pattern> compressValue(const T data);
207 * Decompress a pattern into a value that fits in a dictionary entry.
209 * @param pattern The pattern to be decompressed.
210 * @return The decompressed word.
212 T decompressValue(const Pattern* pattern);
214 /** Clear all dictionary entries. */
215 virtual void resetDictionary();
218 * Add an entry to the dictionary.
220 * @param data The new entry.
222 virtual void addToDictionary(const DictionaryEntry data) = 0;
227 * @param data The cache line to be compressed.
228 * @return Cache line after compression.
230 std::unique_ptr<BaseCacheCompressor::CompressionData> compress(
231 const uint64_t* data);
236 * @param comp_data Compressed cache line.
237 * @param data The cache line to be decompressed.
239 void decompress(const CompressionData* comp_data, uint64_t* data) override;
242 * Turn a value into a dictionary entry.
244 * @param value The value to turn.
245 * @return A dictionary entry containing the value.
247 static DictionaryEntry toDictionaryEntry(T value);
250 * Turn a dictionary entry into a value.
252 * @param The dictionary entry to turn.
253 * @return The value that the dictionary entry contained.
255 static T fromDictionaryEntry(const DictionaryEntry& entry);
258 typedef BaseDictionaryCompressorParams Params;
259 DictionaryCompressor(const Params *p);
260 ~DictionaryCompressor() = default;
264 * The compressed data is composed of multiple pattern entries. To add a new
265 * pattern one should inherit from this class and implement isPattern() and
266 * decompress(). Then the new pattern must be added to the PatternFactory
267 * declaration in crescent order of size (in the DictionaryCompressor class).
270 class DictionaryCompressor<T>::Pattern
273 /** Pattern enum number. */
274 const int patternNumber;
276 /** Code associated to the pattern. */
279 /** Length, in bits, of the code and match location. */
280 const uint8_t length;
282 /** Number of unmatched bits. */
283 const uint8_t numUnmatchedBits;
285 /** Index representing the the match location. */
286 const int matchLocation;
288 /** Wether the pattern allocates a dictionary entry or not. */
293 * Default constructor.
295 * @param number Pattern number.
296 * @param code Code associated to this pattern.
297 * @param metadata_length Length, in bits, of the code and match location.
298 * @param num_unmatched_bits Number of unmatched bits.
299 * @param match_location Index of the match location.
301 Pattern(const int number, const uint64_t code,
302 const uint64_t metadata_length, const uint64_t num_unmatched_bits,
303 const int match_location, const bool allocate = true)
304 : patternNumber(number), code(code), length(metadata_length),
305 numUnmatchedBits(num_unmatched_bits),
306 matchLocation(match_location), allocate(allocate)
310 /** Default destructor. */
311 virtual ~Pattern() = default;
314 * Get enum number associated to this pattern.
316 * @return The pattern enum number.
318 int getPatternNumber() const { return patternNumber; };
321 * Get code of this pattern.
325 uint8_t getCode() const { return code; }
328 * Get the index of the dictionary match location.
330 * @return The index of the match location.
332 uint8_t getMatchLocation() const { return matchLocation; }
335 * Get size, in bits, of the pattern (excluding prefix). Corresponds to
336 * unmatched_data_size + code_length.
343 return numUnmatchedBits + length;
347 * Determine if pattern allocates a dictionary entry.
349 * @return True if should allocate a dictionary entry.
351 bool shouldAllocate() const { return allocate; }
354 * Extract pattern's information to a string.
356 * @return A string containing the relevant pattern metadata.
361 return csprintf("pattern %s (encoding %x, size %u bits)",
362 getPatternNumber(), getCode(), getSizeBits());
366 * Decompress the pattern. Each pattern has its own way of interpreting
369 * @param dict_bytes The bytes in the corresponding matching entry.
370 * @return The decompressed pattern.
372 virtual DictionaryEntry decompress(
373 const DictionaryEntry dict_bytes) const = 0;
377 class DictionaryCompressor<T>::CompData : public CompressionData
380 /** The patterns matched in the original line. */
381 std::vector<std::unique_ptr<Pattern>> entries;
384 ~CompData() = default;
387 * Add a pattern entry to the list of patterns.
389 * @param entry The new pattern entry.
391 virtual void addEntry(std::unique_ptr<Pattern>);
395 * A pattern containing the original uncompressed data. This should be the
396 * worst case of every pattern factory, where if all other patterns fail,
397 * an instance of this pattern is created.
400 class DictionaryCompressor<T>::UncompressedPattern
401 : public DictionaryCompressor<T>::Pattern
404 /** A copy of the original data. */
405 const DictionaryEntry data;
408 UncompressedPattern(const int number,
410 const uint64_t metadata_length,
411 const int match_location,
412 const DictionaryEntry bytes)
413 : DictionaryCompressor<T>::Pattern(number, code, metadata_length,
414 sizeof(T) * 8, match_location, true),
420 isPattern(const DictionaryEntry& bytes, const DictionaryEntry& dict_bytes,
421 const int match_location)
423 // An entry can always be uncompressed
428 decompress(const DictionaryEntry dict_bytes) const override
435 * A pattern that compares masked values against dictionary entries. If
436 * the masked dictionary entry matches perfectly the masked value to be
437 * compressed, there is a pattern match.
439 * For example, if the mask is 0xFF00 (that is, this pattern matches the MSB),
440 * the value (V) 0xFF20 is being compressed, and the dictionary contains
441 * the value (D) 0xFF03, this is a match (V & mask == 0xFF00 == D & mask),
442 * and 0x0020 is added to the list of unmatched bits.
444 * @tparam mask A mask containing the bits that must match.
448 class DictionaryCompressor<T>::MaskedPattern
449 : public DictionaryCompressor<T>::Pattern
452 static_assert(mask != 0, "The pattern's value mask must not be zero. Use "
453 "the uncompressed pattern instead.");
455 /** A copy of the bits that do not belong to the mask. */
459 MaskedPattern(const int number,
461 const uint64_t metadata_length,
462 const int match_location,
463 const DictionaryEntry bytes,
464 const bool allocate = true)
465 : DictionaryCompressor<T>::Pattern(number, code, metadata_length,
466 popCount(~mask), match_location, allocate),
467 bits(DictionaryCompressor<T>::fromDictionaryEntry(bytes) & ~mask)
472 isPattern(const DictionaryEntry& bytes, const DictionaryEntry& dict_bytes,
473 const int match_location)
475 const T masked_bytes =
476 DictionaryCompressor<T>::fromDictionaryEntry(bytes) & mask;
477 const T masked_dict_bytes =
478 DictionaryCompressor<T>::fromDictionaryEntry(dict_bytes) & mask;
479 return (match_location >= 0) && (masked_bytes == masked_dict_bytes);
483 decompress(const DictionaryEntry dict_bytes) const override
485 const T masked_dict_bytes =
486 DictionaryCompressor<T>::fromDictionaryEntry(dict_bytes) & mask;
487 return DictionaryCompressor<T>::toDictionaryEntry(
488 bits | masked_dict_bytes);
493 * A pattern that compares masked values to a masked portion of a fixed value.
494 * If all the masked bits match the provided non-dictionary value, there is a
497 * For example, assume the mask is 0xFF00 (that is, this pattern matches the
498 * MSB), and we are searching for data containing only ones (i.e., the fixed
500 * If the value (V) 0xFF20 is being compressed, this is a match (V & mask ==
501 * 0xFF00 == 0xFFFF & mask), and 0x20 is added to the list of unmatched bits.
502 * If the value (V2) 0x0120 is being compressed, this is not a match
503 * ((V2 & mask == 0x0100) != (0xFF00 == 0xFFFF & mask).
505 * @tparam value The value that is being matched against.
506 * @tparam mask A mask containing the bits that must match the given value.
509 template <T value, T mask>
510 class DictionaryCompressor<T>::MaskedValuePattern
511 : public MaskedPattern<mask>
514 static_assert(mask != 0, "The pattern's value mask must not be zero.");
517 MaskedValuePattern(const int number,
519 const uint64_t metadata_length,
520 const int match_location,
521 const DictionaryEntry bytes,
522 const bool allocate = false)
523 : MaskedPattern<mask>(number, code, metadata_length, match_location,
529 isPattern(const DictionaryEntry& bytes, const DictionaryEntry& dict_bytes,
530 const int match_location)
532 // Compare the masked fixed value to the value being checked for
533 // patterns. Since the dictionary is not being used the match_location
535 const T masked_bytes =
536 DictionaryCompressor<T>::fromDictionaryEntry(bytes) & mask;
537 return ((value & mask) == masked_bytes);
541 decompress(const DictionaryEntry dict_bytes) const override
543 return MaskedPattern<mask>::decompress(
544 DictionaryCompressor<T>::toDictionaryEntry(value));
549 * A pattern that narrows the MaskedPattern by allowing a only single possible
550 * dictionary entry to be matched against.
552 * @tparam mask A mask containing the bits that must match.
553 * @tparam location The index of the single entry allowed to match.
556 template <T mask, int location>
557 class DictionaryCompressor<T>::LocatedMaskedPattern
558 : public MaskedPattern<mask>
561 LocatedMaskedPattern(const int number,
563 const uint64_t metadata_length,
564 const int match_location,
565 const DictionaryEntry bytes)
566 : MaskedPattern<mask>(number, code, metadata_length, match_location,
572 isPattern(const DictionaryEntry& bytes, const DictionaryEntry& dict_bytes,
573 const int match_location)
575 // Besides doing the regular masked pattern matching, the match
576 // location must match perfectly with this instance's
577 return (match_location == location) &&
578 MaskedPattern<mask>::isPattern(bytes, dict_bytes, match_location);
583 * A pattern that checks if dictionary entry sized values are solely composed
584 * of multiple copies of a single value.
586 * For example, if we are looking for repeated bytes in a 1-byte granularity
587 * (RepT is uint8_t), the value 0x3232 would match, however 0x3332 wouldn't.
589 * @tparam RepT The type of the repeated value, which must fit in a dictionary
593 template <class RepT>
594 class DictionaryCompressor<T>::RepeatedValuePattern
595 : public DictionaryCompressor<T>::Pattern
598 static_assert(sizeof(T) > sizeof(RepT), "The repeated value's type must "
599 "be smaller than the dictionary entry's type.");
601 /** The repeated value. */
605 RepeatedValuePattern(const int number,
607 const uint64_t metadata_length,
608 const int match_location,
609 const DictionaryEntry bytes,
610 const bool allocate = true)
611 : DictionaryCompressor<T>::Pattern(number, code, metadata_length,
612 8 * sizeof(RepT), match_location, allocate),
613 value(DictionaryCompressor<T>::fromDictionaryEntry(bytes))
618 isPattern(const DictionaryEntry& bytes, const DictionaryEntry& dict_bytes,
619 const int match_location)
621 // Parse the dictionary entry in a RepT granularity, and if all values
622 // are equal, this is a repeated value pattern. Since the dictionary
623 // is not being used, the match_location is irrelevant
624 T bytes_value = DictionaryCompressor<T>::fromDictionaryEntry(bytes);
625 const RepT rep_value = bytes_value;
626 for (int i = 0; i < (sizeof(T) / sizeof(RepT)); i++) {
627 RepT cur_value = bytes_value;
628 if (cur_value != rep_value) {
631 bytes_value >>= 8 * sizeof(RepT);
637 decompress(const DictionaryEntry dict_bytes) const override
639 // The decompressed value is just multiple consecutive instances of
642 for (int i = 0; i < (sizeof(T) / sizeof(RepT)); i++) {
643 decomp_value <<= 8 * sizeof(RepT);
644 decomp_value |= value;
646 return DictionaryCompressor<T>::toDictionaryEntry(decomp_value);
651 * A pattern that checks whether the difference of the value and the dictionary
652 * entries' is below a certain threshold. If so, the pattern is successful,
653 * and only the delta bits need to be stored.
655 * For example, if the delta can only contain up to 4 bits, and the dictionary
656 * contains the entry 0xA231, the value 0xA232 would be compressible, and
657 * the delta 0x1 would be stored. The value 0xA249, on the other hand, would
658 * not be compressible, since its delta (0x18) needs 5 bits to be stored.
660 * @tparam DeltaSizeBits Size of a delta entry, in number of bits, which
661 * determines the threshold. Must always be smaller
662 * than the dictionary entry type's size.
665 template <std::size_t DeltaSizeBits>
666 class DictionaryCompressor<T>::DeltaPattern
667 : public DictionaryCompressor<T>::Pattern
670 static_assert(DeltaSizeBits < (sizeof(T) * 8),
671 "Delta size must be smaller than base size");
674 * The original value. In theory we should keep only the deltas, but
675 * the dictionary entry is not inserted in the dictionary before the
676 * call to the constructor, so the delta cannot be calculated then.
678 const DictionaryEntry bytes;
681 DeltaPattern(const int number,
683 const uint64_t metadata_length,
684 const int match_location,
685 const DictionaryEntry bytes)
686 : DictionaryCompressor<T>::Pattern(number, code, metadata_length,
687 DeltaSizeBits, match_location, false),
693 * Compares a given value against a base to calculate their delta, and
694 * then determines whether it fits a limited sized container.
696 * @param bytes Value to be compared against base.
697 * @param base_bytes Base value.
698 * @return Whether the value fits in the container.
701 isValidDelta(const DictionaryEntry& bytes,
702 const DictionaryEntry& base_bytes)
704 const typename std::make_signed<T>::type limit = DeltaSizeBits ?
705 mask(DeltaSizeBits - 1) : 0;
707 DictionaryCompressor<T>::fromDictionaryEntry(bytes);
709 DictionaryCompressor<T>::fromDictionaryEntry(base_bytes);
710 const typename std::make_signed<T>::type delta = value - base;
711 return (delta >= -limit) && (delta <= limit);
715 isPattern(const DictionaryEntry& bytes,
716 const DictionaryEntry& dict_bytes, const int match_location)
718 return (match_location >= 0) && isValidDelta(bytes, dict_bytes);
722 decompress(const DictionaryEntry dict_bytes) const override
728 #endif //__MEM_CACHE_COMPRESSORS_DICTIONARY_COMPRESSOR_HH__