101 lines
2.3 KiB
C
101 lines
2.3 KiB
C
/*
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* Copyright (c) 2010 The WebM 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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#include "dboolhuff.h"
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#include "vpx_ports/mem.h"
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#include "vpx_mem/vpx_mem.h"
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int vp8dx_start_decode(BOOL_DECODER *br,
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const unsigned char *source,
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unsigned int source_sz) {
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br->user_buffer_end = source + source_sz;
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br->user_buffer = source;
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br->value = 0;
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br->count = -8;
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br->range = 255;
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if (source_sz && !source)
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return 1;
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/* Populate the buffer */
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vp8dx_bool_decoder_fill(br);
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return 0;
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}
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void vp8dx_bool_decoder_fill(BOOL_DECODER *br) {
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const unsigned char *bufptr;
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const unsigned char *bufend;
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VP8_BD_VALUE value;
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int count;
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bufend = br->user_buffer_end;
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bufptr = br->user_buffer;
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value = br->value;
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count = br->count;
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VP8DX_BOOL_DECODER_FILL(count, value, bufptr, bufend);
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br->user_buffer = bufptr;
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br->value = value;
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br->count = count;
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}
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static int get_unsigned_bits(unsigned num_values) {
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int cat = 0;
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if ((num_values--) <= 1) return 0;
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while (num_values > 0) {
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cat++;
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num_values >>= 1;
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}
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return cat;
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}
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int vp9_inv_recenter_nonneg(int v, int m) {
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if (v > (m << 1)) return v;
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else if ((v & 1) == 0) return (v >> 1) + m;
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else return m - ((v + 1) >> 1);
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}
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int vp8_decode_uniform(BOOL_DECODER *br, int n) {
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int v;
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int l = get_unsigned_bits(n);
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int m = (1 << l) - n;
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if (!l) return 0;
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v = vp8_decode_value(br, l - 1);
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if (v < m)
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return v;
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else
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return (v << 1) - m + vp8_decode_value(br, 1);
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}
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int vp8_decode_term_subexp(BOOL_DECODER *br, int k, int num_syms) {
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int i = 0, mk = 0, word;
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while (1) {
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int b = (i ? k + i - 1 : k);
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int a = (1 << b);
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if (num_syms <= mk + 3 * a) {
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word = vp8_decode_uniform(br, num_syms - mk) + mk;
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break;
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} else {
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if (vp8_decode_value(br, 1)) {
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i++;
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mk += a;
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} else {
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word = vp8_decode_value(br, b) + mk;
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break;
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}
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}
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}
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return word;
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}
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