[f0fd47] | 1 | #ifndef CACHE_H |
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| 2 | #define CACHE_H |
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| 3 | |
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| 4 | #include <string> |
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| 5 | #include <list> |
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| 6 | |
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[308a766] | 7 | // #include <assert.h> |
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| 8 | // using namespace std; |
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[f0fd47] | 9 | |
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| 10 | /*! \class Cache |
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| 11 | \brief Class Cache is a template-implementation of a cache with |
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| 12 | arbitrary classes for representing keys and values, respectively. |
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| 13 | |
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| 14 | Each entry of the cache is of the form <em>key --> value</em>, |
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| 15 | where \e key is an instance of some \c KeyClass, and \e value |
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| 16 | an instance of some \c ValueClass.<br><br> |
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| 17 | This implementation comes with the possibility to define bounds |
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| 18 | on both the number of cached pairs <em>key --> value</em> and on |
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| 19 | the total \e weight of the cache.<br> |
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| 20 | Here, the \e weight of a cache is defined as the sum |
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| 21 | of \e weights of all cached values, where the \e weight of each value |
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| 22 | needs to be implemented in the actual class \c ValueClass. |
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| 23 | An example for the weight of a cached value |
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| 24 | may simply be its size in bytes, or may capture some other useful notion |
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| 25 | of how \e heavy the value is. E.g., when caching polynomials, the \e weight |
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| 26 | may be defined to be equal to the number of its monomials.<br><br> |
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| 27 | The <em>key --> value</em> pairs of a cache are being stored in two |
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| 28 | standard lists \c _key and \c _value of equal length <em>L</em>.<br> |
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| 29 | In order to enable a fast |
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| 30 | value lookup, the vector \c _key maintains an ordering such that<br> |
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| 31 | <em> i < j ==> _key[i] < _key[j],</em><br> |
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| 32 | where the right-hand side comparator |
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| 33 | \e < needs to be implemented by class \c KeyClass. Note that this |
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| 34 | ordering allows for value lookup in time <em>O(log(L))</em>, when given |
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| 35 | a specific key.<br><br> |
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| 36 | In addition to \c _key and \c _value, there is a third book-keeping |
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| 37 | structure in Cache: The vector \c _rank of integers captures ranking |
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| 38 | information among all cached values. More concretely,<br> |
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| 39 | <em>_rank : {0, 1, 2, ..., L - 1} --> {0, 1, 2, ..., L - 1}</em><br> |
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| 40 | is a bijection with the semantic<br> |
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| 41 | <em>_rank[s] < _rank[t] :<==> _value[_rank[s]] < _value[_rank[t]],</em><br> |
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| 42 | where the right-hand side comparator \e < needs to be |
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| 43 | implemented by class \c ValueClass. The intention here is that any relation |
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| 44 | <em>_rank[s] < _rank[t]</em> |
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| 45 | is to imply that the key-value pair |
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| 46 | <em>_key[_rank[t]] --> _value[_rank[t]]</em> will be kept at least as |
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| 47 | long in cache as <em> _key[_rank[s]] --> _value[_rank[s]]</em>. |
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| 48 | (I.e., loosely speaking, the higher the rank, the longer a pair is going |
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| 49 | to be cached.)<br><br> |
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| 50 | Whenever the cache becomes either too large (in terms of number of |
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| 51 | entries), or too \e heavy (in terms of accumulated weight), it will |
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| 52 | automatically shrink until both bounds will have been re-established. To |
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| 53 | this end, the <em>key --> value</em> pair with least value rank will be |
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| 54 | erased from the cache. This process is repeated until the cache is small |
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| 55 | enough again, in terms of both the number of entries and the \e weight. |
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| 56 | (Note that it may be necessary to erase numerous pairs after inserting |
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| 57 | just one <em>key --> value</em> when this value's \e weight is |
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| 58 | unproportionally high.)<br><br> |
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| 59 | In order to make the above procedures work, the two template classes |
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| 60 | \c KeyClass and \c ValueClass need to implement the following methods:<br> |
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| 61 | <c>bool KeyClass::operator< (const KeyClass& key),</c><br> |
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| 62 | <c>bool KeyClass::operator== (const KeyClass& key),</c><br> |
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| 63 | <c>bool ValueClass::operator< (const ValueClass& key),</c><br> |
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| 64 | <c>bool ValueClass::operator== (const ValueClass& key),</c><br> |
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| 65 | <c>int ValueClass::getWeight ().</c> |
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| 66 | \author Frank Seelisch, http://www.mathematik.uni-kl.de/~seelisch |
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| 67 | */ |
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[f1cee38] | 68 | template<class KeyClass, class ValueClass> class Cache |
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[f0fd47] | 69 | { |
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| 70 | private: |
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| 71 | /** |
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| 72 | * A bijection on the set {0, ..., _key.size() - 1}.<br> |
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| 73 | * Semantically, <c>_rank(j) > _rank(i)</c> means that the pair |
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| 74 | * <c>key(_rank(j)) --> value(_rank(j))</c> will be cached at least |
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| 75 | * as long as the pair <c>key(_rank(i)) --> value(_rank(i))</c>. |
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| 76 | */ |
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[308a766] | 77 | std::list<int> _rank; |
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[a9c298] | 78 | |
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[f0fd47] | 79 | /** |
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| 80 | * _key is sorted in ascending order, i.e., |
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| 81 | * <em>j < i ==> _key(j) < _key(i),</em> |
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| 82 | * where the right-hand side comparator "<" needs to be implemented |
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| 83 | * in KeyClass. |
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| 84 | */ |
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[308a766] | 85 | std::list<KeyClass> _key; |
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[a9c298] | 86 | |
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[f0fd47] | 87 | /** |
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| 88 | * _value captures the actual objects of interest;<br> |
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| 89 | * \c _value[i] corresponds to \c _key[i] and may be retrieved |
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| 90 | * by calling Cache::getValue (const KeyClass&) const with the |
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| 91 | * argument \c _key[i]). |
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| 92 | */ |
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[308a766] | 93 | std::list<ValueClass> _value; |
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[a9c298] | 94 | |
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[f0fd47] | 95 | /** |
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| 96 | * container for the weights of all cached values |
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| 97 | */ |
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[308a766] | 98 | std::list<int> _weights; |
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[a9c298] | 99 | |
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[f0fd47] | 100 | /** |
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| 101 | * a pointer to some element of _key; |
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| 102 | * We make this mutable so that methods which leave the cache |
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| 103 | * unmodified but which alter _itKey can still be declared as |
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| 104 | * const, as the user would expect for these methods. |
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| 105 | */ |
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[308a766] | 106 | mutable typename std::list<KeyClass>::const_iterator _itKey; |
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[a9c298] | 107 | |
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[f0fd47] | 108 | /** |
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| 109 | * a pointer to some element of _value; |
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| 110 | * We make this mutable so that methods which leave the cache |
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| 111 | * unmodified but which alter _itValue can still be declared as |
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| 112 | * const, as the user would expect for these methods. |
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| 113 | */ |
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[308a766] | 114 | mutable typename std::list<ValueClass>::const_iterator _itValue; |
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[a9c298] | 115 | |
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[f0fd47] | 116 | /** |
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| 117 | * for storing the momentary weight of the given cache;<br> |
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| 118 | * This is the sum of \c _value[i].getWeight() over all \e i, |
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| 119 | * i.e., over all cached values. Equivalently, this is equal |
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| 120 | * to all weights stored in _weights. |
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| 121 | */ |
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| 122 | int _weight; |
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[a9c298] | 123 | |
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[f0fd47] | 124 | /** |
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| 125 | * the bound for the number of cached <c>key --> value</c> pairs;<br> |
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| 126 | * The cache will automatically ensure that this bound will never be |
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| 127 | * exceeded; |
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| 128 | * see Cache::shrink (const KeyClass&) and Cache::deleteLast (). |
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| 129 | */ |
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| 130 | int _maxEntries; |
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[a9c298] | 131 | |
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[f0fd47] | 132 | /** |
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| 133 | * the bound on total cache weight;<br> |
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| 134 | * The cache will automatically ensure that this bound will never be |
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| 135 | * exceeded; see |
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| 136 | * see Cache::shrink (const KeyClass&) and Cache::deleteLast (). |
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| 137 | */ |
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| 138 | int _maxWeight; |
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[a9c298] | 139 | |
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[f0fd47] | 140 | /** |
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| 141 | * A method for providing the index of a given key in the vector _key. |
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| 142 | * Either _key contains the given key, then its index will be returned. |
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| 143 | * Otherwise the position in _key, at which the given key should be placed |
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| 144 | * (with respect to the ordering in _key) is returned. |
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| 145 | * @param key an instance of KeyClass |
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| 146 | * @return the actual or would-be index of key in _key |
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| 147 | * @see Cache::hasKey (const KeyClass&) const |
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| 148 | */ |
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| 149 | int getIndexInKey (const KeyClass& key) const; |
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[a9c298] | 150 | |
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[f0fd47] | 151 | /** |
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| 152 | * A method for providing the index of a given value in the vector _rank. |
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| 153 | * Based on the rank of the given value, the position in _rank at which |
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| 154 | * the given value should be inserted, is returned. |
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| 155 | * (The method also works, when the given value is already contained in |
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| 156 | * the cache.) |
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| 157 | * @param value an instance of ValueClass |
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| 158 | * @return the actual or would-be index of value in _rank |
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| 159 | */ |
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| 160 | int getIndexInRank (const ValueClass& value) const; |
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[a9c298] | 161 | |
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[f0fd47] | 162 | /** |
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| 163 | * A method for shrinking the given cache so that it meet the bounds on |
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| 164 | * the maximum number of entries and total weight again. |
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| 165 | * The method returns true iff the process of shrinking deleted a pair |
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| 166 | * (k --> v) from the cache such that k equals the given key. |
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| 167 | * @param key an instance of KeyClass |
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| 168 | * @return true iff shrinking deleted a pair (key --> *) |
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| 169 | */ |
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| 170 | bool shrink (const KeyClass& key); |
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[a9c298] | 171 | |
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[f0fd47] | 172 | /** |
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| 173 | * A method for deleting the least-ranked cache entry. |
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| 174 | * The method returns true iff the deleted pair (k --> v) |
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| 175 | * satisfies k == key. |
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| 176 | * @param key an instance of KeyClass |
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| 177 | * @return true iff a pair (key --> *) was deleted |
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| 178 | */ |
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| 179 | bool deleteLast (const KeyClass& key); |
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| 180 | public: |
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| 181 | /** |
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| 182 | * A constructor for class Cache. |
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| 183 | * The method makes sure that all member vectors be empty. |
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| 184 | */ |
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| 185 | Cache(); |
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[a9c298] | 186 | |
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[f0fd47] | 187 | /** |
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| 188 | * A destructor for class Cache. |
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| 189 | * The method clears all member vectors. (This includes that |
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| 190 | * destructors are invoked, accordingly.) |
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| 191 | */ |
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| 192 | ~Cache(); |
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[a9c298] | 193 | |
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[f0fd47] | 194 | /** |
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| 195 | * Copy implementation for class Cache. |
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| 196 | * Apart from copying all flat members, all vectors are being |
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| 197 | * deep-copied. |
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| 198 | */ |
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| 199 | Cache (const Cache& c); |
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[a9c298] | 200 | |
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[f0fd47] | 201 | /** |
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| 202 | * A user-suited constructor for class Cache. |
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| 203 | * The method makes sure that all member vectors be empty. |
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| 204 | * Moreover, the user can provide bounds for the maximum |
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| 205 | * number of entries in the cache, and for the total weight |
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| 206 | * of the cache. |
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| 207 | * @param maxEntries the (positive) maximum number of pairs |
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| 208 | (key --> value) in the cache |
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| 209 | * @param maxWeight the (positive) maximum weight of the cache |
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| 210 | */ |
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| 211 | Cache (const int maxEntries, const int maxWeight); |
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[a9c298] | 212 | |
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[f0fd47] | 213 | /** |
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| 214 | * A method for retrieving the momentary weight of the cache. |
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| 215 | * The return value will always be less than or equal to the result |
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| 216 | * of Cache::getMaxWeight () const.<br> |
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| 217 | * Semantically, the total weight of a cache is the sum of weights |
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| 218 | * of all cached values. |
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| 219 | * @return the momentary weight of the cache |
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| 220 | * @see Cache::getMaxWeight () const |
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| 221 | * @see MinorValue::getWeight () const |
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| 222 | */ |
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| 223 | int getWeight () const; |
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[a9c298] | 224 | |
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[f0fd47] | 225 | /** |
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| 226 | * A method for retrieving the momentary number of (key --> value) pairs |
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| 227 | * in the cache. |
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| 228 | * The return value will always be less than or equal to the result of |
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| 229 | * Cache::getMaxNumberOfEntries () const. |
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| 230 | * @return the momentary number of cached values of the cache |
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| 231 | * @see Cache::getMaxNumberOfEntries () const |
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| 232 | */ |
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| 233 | int getNumberOfEntries () const; |
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[a9c298] | 234 | |
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[f0fd47] | 235 | /** |
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| 236 | * A method for retrieving the maximum number of (key --> value) pairs |
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| 237 | * in the cache. |
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| 238 | * @return the maximum number of cached values of the cache |
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| 239 | * @see Cache::getNumberOfEntries () const |
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| 240 | * @see Cache::Cache (const int, const int) |
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| 241 | */ |
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| 242 | int getMaxNumberOfEntries () const; |
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[a9c298] | 243 | |
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[f0fd47] | 244 | /** |
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| 245 | * A method for retrieving the maximum weight of the cache. |
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| 246 | * @return the maximum weight of the cache |
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| 247 | * @see Cache::getWeight () const |
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| 248 | * @see Cache::Cache (const int, const int) |
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| 249 | */ |
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| 250 | int getMaxWeight () const; |
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[a9c298] | 251 | |
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[f0fd47] | 252 | /** |
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| 253 | * Checks whether the cache contains a pair (k --> v) such that |
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| 254 | * k equals the given key. |
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| 255 | * If so, the method returns true; false otherwise. |
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| 256 | * In order to make Cache::getValue (const KeyClass&) const |
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| 257 | * work properly, the user is strongly adviced to always check key |
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| 258 | * containment by means of Cache::hasKey (const KeyClass&) const. |
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| 259 | * (The implementation at hand ensures that invoking hasKey and |
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| 260 | * getValue does not result in extra computational efforts.) |
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| 261 | * @param key the key for which containment is to be checked |
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| 262 | * @return true iff the cache contains the given key |
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| 263 | * @see Cache::getValue (const KeyClass&) const |
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| 264 | */ |
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| 265 | bool hasKey (const KeyClass& key) const; |
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[a9c298] | 266 | |
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[f0fd47] | 267 | /** |
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| 268 | * Returns the value for a given key. |
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| 269 | * The method assumes that there is actually an entry of the form |
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| 270 | * (key --> *) in the cache. This can be checked before using |
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| 271 | * Cache::hasKey (const KeyClass&) const. (Note that calling |
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| 272 | * both methods in direct succession does not result in extra |
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| 273 | * computational efforts.) |
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| 274 | * \par Assertions |
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| 275 | * If the given key is not contained in the cache, program execution |
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| 276 | * will be stopped. |
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| 277 | * @param key the key, for which the corresponding value is to be returned |
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| 278 | * @return the value corresponding to the given key |
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| 279 | * @see Cache::hasKey (const KeyClass&) const |
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| 280 | */ |
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| 281 | ValueClass getValue (const KeyClass& key) const; |
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[a9c298] | 282 | |
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[f0fd47] | 283 | /** |
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| 284 | * Inserts the pair (key --> value) in the cache. |
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| 285 | * If there is already some entry (key --> value'), then value will be |
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| 286 | * replaced by value'. |
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| 287 | * As putting some new pair in the cache may result in a violation |
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| 288 | * of the maximal number of entries or the weight of the cache, or both, |
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| 289 | * Cache::put (const KeyClass&, const ValueClass&) will always finalize by |
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| 290 | * calling the private method Cache::shrink(const KeyClass&), in order to |
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| 291 | * re-establish both bounds. Note that this may even result in deleting the |
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| 292 | * newly inserted pair (key --> value).<br> |
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| 293 | * Because of that undesirable but possible effect, the method returns |
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| 294 | * whether the pair is actually contained in the cache after invokation of |
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| 295 | * Cache::put (const KeyClass&, const ValueClass&). |
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| 296 | * @param key an instance of KeyClass |
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| 297 | * @param value an instance of ValueClass |
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| 298 | * @return whether the pair (key --> value) is contained in the modified |
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| 299 | * cache |
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| 300 | * @see Cache::getValue (const KeyClass&) const |
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| 301 | */ |
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| 302 | bool put (const KeyClass& key, const ValueClass& value); |
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[a9c298] | 303 | |
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[f0fd47] | 304 | /** |
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| 305 | * Clears the cache so that it has no entry. This method will also |
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| 306 | * enforce destruction of all former entries of the cache. |
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| 307 | */ |
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| 308 | void clear (); |
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[a9c298] | 309 | |
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[f0fd47] | 310 | /** |
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| 311 | * A method for providing a printable version of the represented |
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| 312 | * cache, including all contained (key --> value) pairs. |
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| 313 | * @return a printable version of the given instance as instance of class |
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| 314 | * string |
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| 315 | */ |
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[308a766] | 316 | std::string toString () const; |
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[a9c298] | 317 | |
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[f0fd47] | 318 | /** |
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| 319 | * A method for printing a string representation of the given cache to |
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| 320 | * std::cout. This includes string representations of all contained |
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| 321 | * (key --> value) pairs. |
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| 322 | */ |
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| 323 | void print () const; |
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| 324 | }; |
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| 325 | |
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[aa8a7e] | 326 | #include "kernel/linear_algebra/CacheImplementation.h" |
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[f0fd47] | 327 | |
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| 328 | #endif |
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| 329 | /* CACHE_H */ |
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