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65 lines
1.5 KiB
C
65 lines
1.5 KiB
C
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/*
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* Copyright (c) 2010 The VP8 project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#ifndef tree_reader_h
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#define tree_reader_h 1
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#include "treecoder.h"
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#include "dboolhuff.h"
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typedef BOOL_DECODER vp8_reader;
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#define vp8_read vp8dx_decode_bool
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#define vp8_read_literal vp8_decode_value
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#define vp8_read_bit( R) vp8_read( R, vp8_prob_half)
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/* Intent of tree data structure is to make decoding trivial. */
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static int vp8_treed_read(
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vp8_reader *const r, /* !!! must return a 0 or 1 !!! */
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vp8_tree t,
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const vp8_prob *const p
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)
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{
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register vp8_tree_index i = 0;
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while ((i = t[ i + vp8_read(r, p[i>>1])]) > 0) ;
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return -i;
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}
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/* Variant reads a binary number given distributions on each bit.
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Note that tree is arbitrary; probability of decoding a zero
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may or may not depend on previously decoded bits. */
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static int vp8_treed_read_num(
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vp8_reader *const r, /* !!! must return a 0 or 1 !!! */
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vp8_tree t,
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const vp8_prob *const p
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)
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{
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vp8_tree_index i = 0;
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int v = 0, b;
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do
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{
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b = vp8_read(r, p[i>>1]);
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v = (v << 1) + b;
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}
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while ((i = t[i+b]) > 0);
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return v;
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}
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#endif /* tree_reader_h */
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