153 lines
6 KiB
C++
153 lines
6 KiB
C++
///////////////////////////////////////////////////////////////////////////
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//
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// Copyright (c) 2009-2014 DreamWorks Animation LLC.
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//
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of DreamWorks Animation nor the names of
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// its contributors may be used to endorse or promote products derived
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// from this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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//
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///////////////////////////////////////////////////////////////////////////
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#ifndef INCLUDED_IMF_FAST_HUF_H
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#define INCLUDED_IMF_FAST_HUF_H
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#include "ImfInt64.h"
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#include "ImfNamespace.h"
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#include "ImfExport.h"
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OPENEXR_IMF_INTERNAL_NAMESPACE_HEADER_ENTER
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//
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// Alternative Canonical Huffman decoder:
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//
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// Canonical Huffman decoder based on 'On the Implementation of Minimum
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// Redundancy Prefix Codes' by Moffat and Turpin - highly recommended
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// reading as a good description of the problem space, as well as
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// a fast decoding algorithm.
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//
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// The premise is that instead of working directly with the coded
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// symbols, we create a new ordering based on the frequency of symbols.
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// Less frequent symbols (and thus longer codes) are ordered earler.
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// We're calling the values in this ordering 'Ids', as oppsed to
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// 'Symbols' - which are the short values we eventually want decoded.
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//
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// With this new ordering, a few small tables can be derived ('base'
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// and 'offset') which drive the decoding. To cut down on the
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// linear scanning of these tables, you can add a small table
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// to directly look up short codes (as you might in a traditional
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// lookup-table driven decoder).
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//
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// The decoder is meant to be compatible with the encoder (and decoder)
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// in ImfHuf.cpp, just faster. For ease of implementation, this decoder
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// should only be used on compressed bitstreams >= 128 bits long.
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//
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class FastHufDecoder
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{
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public:
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//
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// Longest compressed code length that ImfHuf supports (58 bits)
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//
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static const int MAX_CODE_LEN = 58;
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//
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// Number of bits in our acceleration table. Should match all
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// codes up to TABLE_LOOKUP_BITS in length.
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//
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static const int TABLE_LOOKUP_BITS = 12;
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IMF_EXPORT
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FastHufDecoder (const char*& table,
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int numBytes,
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int minSymbol,
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int maxSymbol,
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int rleSymbol);
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IMF_EXPORT
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~FastHufDecoder ();
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IMF_EXPORT
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static bool enabled ();
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IMF_EXPORT
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void decode (const unsigned char *src,
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int numSrcBits,
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unsigned short *dst,
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int numDstElems);
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private:
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void buildTables (Int64*, Int64*);
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void refill (Int64&, int, Int64&, int&, const unsigned char *&, int&);
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Int64 readBits (int, Int64&, int&, const char *&);
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int _rleSymbol; // RLE symbol written by the encoder.
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// This could be 65536, so beware
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// when you use shorts to hold things.
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int _numSymbols; // Number of symbols in the codebook.
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unsigned char _minCodeLength; // Minimum code length, in bits.
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unsigned char _maxCodeLength; // Maximum code length, in bits.
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int *_idToSymbol; // Maps Ids to symbols. Ids are a symbol
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// ordering sorted first in terms of
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// code length, and by code within
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// the same length. Ids run from 0
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// to mNumSymbols-1.
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Int64 _ljBase[MAX_CODE_LEN + 1]; // the 'left justified base' table.
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// Takes base[i] (i = code length)
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// and 'left justifies' it into an Int64
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Int64 _ljOffset[MAX_CODE_LEN +1 ]; // There are some other terms that can
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// be folded into constants when taking
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// the 'left justified' decode path. This
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// holds those constants, indexed by
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// code length
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//
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// We can accelerate the 'left justified' processing by running the
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// top TABLE_LOOKUP_BITS through a LUT, to find the symbol and code
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// length. These are those acceleration tables.
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//
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// Even though our evental 'symbols' are ushort's, the encoder adds
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// a symbol to indicate RLE. So with a dense code book, we could
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// have 2^16+1 codes, so both mIdToSymbol and mTableSymbol need
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// to be bigger than 16 bits.
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//
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int _tableSymbol[1 << TABLE_LOOKUP_BITS];
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unsigned char _tableCodeLen[1 << TABLE_LOOKUP_BITS];
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Int64 _tableMin;
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};
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OPENEXR_IMF_INTERNAL_NAMESPACE_HEADER_EXIT
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#endif
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