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Diffstat (limited to 'stoc/source/security/lru_cache.h')
| -rw-r--r-- | stoc/source/security/lru_cache.h | 210 |
1 files changed, 210 insertions, 0 deletions
diff --git a/stoc/source/security/lru_cache.h b/stoc/source/security/lru_cache.h new file mode 100644 index 000000000..402b41d58 --- /dev/null +++ b/stoc/source/security/lru_cache.h @@ -0,0 +1,210 @@ +/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */ +/* + * This file is part of the LibreOffice project. + * + * This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. + * + * This file incorporates work covered by the following license notice: + * + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed + * with this work for additional information regarding copyright + * ownership. The ASF licenses this file to you under the Apache + * License, Version 2.0 (the "License"); you may not use this file + * except in compliance with the License. You may obtain a copy of + * the License at http://www.apache.org/licenses/LICENSE-2.0 . + */ +#ifndef INCLUDED_STOC_SOURCE_SECURITY_LRU_CACHE_H +#define INCLUDED_STOC_SOURCE_SECURITY_LRU_CACHE_H + +#include <memory> +#include <unordered_map> + +// __CACHE_DIAGNOSE works only for OUString keys +#ifdef __CACHE_DIAGNOSE +#include <osl/diagnose.h> +#include <rtl/ustrbuf.hxx> +#include <rtl/ustring.hxx> +#include <rtl/string.hxx> +#include <sal/log.hxx> +#endif + + +namespace stoc_sec +{ + +/** Implementation of a least recently used (lru) cache. +*/ +template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey > +class lru_cache +{ + struct Entry + { + t_key m_key; + t_val m_val; + Entry * m_pred; + Entry * m_succ; + }; + typedef std::unordered_map< t_key, Entry *, t_hashKey, t_equalKey > t_key2element; + t_key2element m_key2element; + ::std::size_t m_size; + + std::unique_ptr<Entry[]> m_block; + mutable Entry * m_head; + mutable Entry * m_tail; + inline void toFront( Entry * entry ) const; + +public: + /** Default Ctor. Does not cache. + */ + inline lru_cache(); + + /** Retrieves a pointer to value in cache. Returns 0, if none was found. + + @param key a key + @return pointer to value or 0 + */ + inline t_val const * lookup( t_key const & key ) const; + + /** Sets a value to be cached for given key. + + @param key a key + @param val a value + */ + inline void set( t_key const & key, t_val const & val ); + + /** Sets the number of elements to be cached. This will clear previous entries. + + @param cacheSize number of elements to be cached + */ + inline void setSize( ::std::size_t size ); +}; + +template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey > +inline void lru_cache< t_key, t_val, t_hashKey, t_equalKey >::setSize( + ::std::size_t size ) +{ + m_key2element.clear(); + m_block.reset(); + m_size = size; + + if (0 < m_size) + { + m_block.reset( new Entry[ m_size ] ); + m_head = m_block.get(); + m_tail = m_block.get() + m_size -1; + for ( ::std::size_t nPos = m_size; nPos--; ) + { + m_block[ nPos ].m_pred = m_block.get() + nPos -1; + m_block[ nPos ].m_succ = m_block.get() + nPos +1; + } + } +} + +template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey > +inline lru_cache< t_key, t_val, t_hashKey, t_equalKey >::lru_cache() + : m_size( 0 ) + , m_block( nullptr ) + , m_head( nullptr ) + , m_tail( nullptr ) +{ +} + +template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey > +inline void lru_cache< t_key, t_val, t_hashKey, t_equalKey >::toFront( + Entry * entry ) const +{ + if (entry != m_head) + { + // cut out element + if (entry == m_tail) + { + m_tail = entry->m_pred; + } + else + { + entry->m_succ->m_pred = entry->m_pred; + entry->m_pred->m_succ = entry->m_succ; + } + // push to front + m_head->m_pred = entry; + entry->m_succ = m_head; + m_head = entry; + } +} + +template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey > +inline t_val const * lru_cache< t_key, t_val, t_hashKey, t_equalKey >::lookup( + t_key const & key ) const +{ + if (0 < m_size) + { + typename t_key2element::const_iterator const iFind( m_key2element.find( key ) ); + if (iFind != m_key2element.end()) + { + Entry * entry = iFind->second; + toFront( entry ); +#ifdef __CACHE_DIAGNOSE + OUStringBuffer buf( 48 ); + buf.appendAscii( "> retrieved element \"" ); + buf.append( entry->m_key ); + buf.appendAscii( "\" from cache" ); + SAL_INFO("stoc", buf.makeStringAndClear() ); +#endif + return &entry->m_val; + } + } + return nullptr; +} + +template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey > +inline void lru_cache< t_key, t_val, t_hashKey, t_equalKey >::set( + t_key const & key, t_val const & val ) +{ + if (0 < m_size) + { + typename t_key2element::const_iterator const iFind( m_key2element.find( key ) ); + + Entry * entry; + if (iFind == m_key2element.end()) + { + entry = m_tail; // erase last element +#ifdef __CACHE_DIAGNOSE + if (entry->m_key.getLength()) + { + OUStringBuffer buf( 48 ); + buf.appendAscii( "> kicking element \"" ); + buf.append( entry->m_key ); + buf.appendAscii( "\" from cache" ); + SAL_INFO("stoc", buf.makeStringAndClear() ); + } +#endif + m_key2element.erase( entry->m_key ); + entry->m_key = key; + ::std::pair< typename t_key2element::iterator, bool > insertion( + m_key2element.emplace( key, entry ) ); + OSL_ENSURE( insertion.second, "### inserting new cache entry failed?!" ); + } + else + { + entry = iFind->second; +#ifdef __CACHE_DIAGNOSE + OUStringBuffer buf( 48 ); + buf.appendAscii( "> replacing element \"" ); + buf.append( entry->m_key ); + buf.appendAscii( "\" in cache" ); + SAL_INFO("stoc", buf.makeStringAndClear() ); +#endif + } + entry->m_val = val; + toFront( entry ); + } +} + +} + +#endif + +/* vim:set shiftwidth=4 softtabstop=4 expandtab: */ |