89 lines
2.9 KiB
C
89 lines
2.9 KiB
C
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//compress_detect.h
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//粗略估算数据的可压缩性 for diff.
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/*
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The MIT License (MIT)
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Copyright (c) 2012-2017 HouSisong
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Permission is hereby granted, free of charge, to any person
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obtaining a copy of this software and associated documentation
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files (the "Software"), to deal in the Software without
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restriction, including without limitation the rights to use,
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copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the
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Software is furnished to do so, subject to the following
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conditions:
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The above copyright notice and this permission notice shall be
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included in all copies of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
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OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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OTHER DEALINGS IN THE SOFTWARE.
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*/
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#ifdef _MSC_VER
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#pragma warning( disable : 4706)
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#endif
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#ifndef compress_detect_h
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#define compress_detect_h
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#include <stddef.h> //for size_t
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#include "../../HPatch/patch_types.h" //for hpatch_uint32_t
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#include "mem_buf.h"
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namespace hdiff_private{
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template<class _UInt>
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static unsigned int _getUIntCost(_UInt v){
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if ((sizeof(_UInt)<8)||((v>>28)>>28)==0) {
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int cost=1;
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_UInt t;
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if ((t=(v>>28))) { v=t; cost+=4; }
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if ((t=(v>>14))) { v=t; cost+=2; }
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if ((t=(v>> 7))) { v=t; ++cost; }
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return cost;
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}else{
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return 9;
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}
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}
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template<class _Int,class _UInt>
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inline static unsigned _getIntCost(_Int v){
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return _getUIntCost((_UInt)(2*((v>=0)?(_UInt)v:(_UInt)(-v))));
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}
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//粗略估算该区域存储成本.
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size_t getRegionRleCost(const unsigned char* d,size_t n,const unsigned char* sub=0,
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unsigned char* out_nocompress=0,size_t* nocompressSize=0);
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class TCompressDetect{
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public:
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TCompressDetect();
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~TCompressDetect();
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void add_chars(const unsigned char* d,size_t n,const unsigned char* sub=0);
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size_t cost(const unsigned char* d,size_t n,const unsigned char* sub=0)const;
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private:
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struct TCharConvTable{
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hpatch_uint32_t sum;
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hpatch_uint32_t sum1char[256];
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hpatch_uint32_t sum2char[256*256];//用相邻字符转换几率来近似估计数据的可压缩性.
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unsigned char cache[1];//实际大小为kCacheSize,超出该距离的旧数据会被清除.
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};
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TAutoMem m_mem;
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TCharConvTable* m_table;
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int m_lastChar;
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int m_lastPopChar;
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hpatch_uint32_t m_cacheBegin;
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hpatch_uint32_t m_cacheEnd;
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void clear();
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void _add_rle(const unsigned char* d,size_t n);
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size_t _cost_rle(const unsigned char* d,size_t n)const;
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};
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}//namespace hdiff_private
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#endif
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