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https://github.com/webmproject/libwebp.git
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87 lines
2.5 KiB
C
87 lines
2.5 KiB
C
// Copyright 2011 Google Inc. All Rights Reserved.
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//
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// This code is licensed under the same terms as WebM:
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// Software License Agreement: http://www.webmproject.org/license/software/
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// Additional IP Rights Grant: http://www.webmproject.org/license/additional/
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// -----------------------------------------------------------------------------
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//
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// Tree-coder using VP8's boolean coder
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//
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// Symbols are stored as nodes of a tree that records their frequencies and
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// is dynamically updated.
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//
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// Author: Skal (pascal.massimino@gmail.com)
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//
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// Encoding example:
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/*
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static int Compress(const uint8_t* src, int src_length,
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uint8_t** output, size_t* output_size) {
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int i;
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TCoder* coder = TCoderNew(255);
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VP8BitWriter bw;
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VP8BitWriterInit(&bw, 0);
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for (i = 0; i < src_length; ++i)
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TCoderEncode(coder, src[i], &bw);
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TCoderDelete(coder);
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VP8BitWriterFinish(&bw);
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*output = VP8BitWriterBuf(&bw);
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*output_size = VP8BitWriterSize(&bw);
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return !bw.error_;
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}
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*/
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//
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// Decoding example:
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/*
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static int Decompress(const uint8_t* src, size_t src_size,
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uint8_t* dst, int dst_length) {
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int i;
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TCoder* coder = TCoderNew(255);
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VP8BitReader br;
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VP8InitBitReader(&br, src, src + src_size);
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for (i = 0; i < dst_length; ++i)
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dst[i] = TCoderDecode(coder, &br);
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TCoderDelete(coder);
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return !br.eof_;
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}
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*/
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#ifndef WEBP_UTILS_TCODER_H_
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#define WEBP_UTILS_TCODER_H_
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#if defined(__cplusplus) || defined(c_plusplus)
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extern "C" {
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#endif
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struct VP8BitReader;
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struct VP8BitWriter;
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typedef struct TCoder TCoder;
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// Creates a tree-coder capable of coding symbols in
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// the [0, max_symbol] range. Returns NULL in case of memory error.
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// 'max_symbol' must be in the range [0, TCODER_MAX_SYMBOL)
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#define TCODER_MAX_SYMBOL (1 << 24)
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TCoder* TCoderNew(int max_symbol);
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// Re-initialize an existing object, make it ready for a new encoding or
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// decoding cycle.
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void TCoderInit(TCoder* const c);
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// destroys the tree-coder object and frees memory.
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void TCoderDelete(TCoder* const c);
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// Code next symbol 's'. If the bit-writer 'bw' is NULL, the function will
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// just record the symbol, and update the internal frequency counters.
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void TCoderEncode(TCoder* const c, int s, struct VP8BitWriter* const bw);
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// Decode and return next symbol.
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int TCoderDecode(TCoder* const c, struct VP8BitReader* const br);
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// Theoretical number of bits needed to code 'symbol' in the current state.
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double TCoderSymbolCost(const TCoder* const c, int symbol);
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#if defined(__cplusplus) || defined(c_plusplus)
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} // extern "C"
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#endif
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#endif // WEBP_UTILS_TCODER_H_
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