mirror of
https://github.com/RGBCube/serenity
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1dfb065a9c
The marker bit is VP9-only, so move that into a new initialize_vp9() function. finish_decode() is VP9-only, so rename that to finish_decode_vp9().
87 lines
2.7 KiB
C++
87 lines
2.7 KiB
C++
/*
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* Copyright (c) 2021, Hunter Salyer <thefalsehonesty@gmail.com>
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* Copyright (c) 2022, Gregory Bertilson <zaggy1024@gmail.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/BuiltinWrappers.h>
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#include "BooleanDecoder.h"
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namespace Gfx {
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ErrorOr<BooleanDecoder> BooleanDecoder::initialize(MaybeOwned<BigEndianInputBitStream> bit_stream, size_t size_in_bytes)
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{
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VERIFY(bit_stream->is_aligned_to_byte_boundary());
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auto value = TRY(bit_stream->read_value<u8>());
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u8 range = 255;
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u64 bits_left = (8 * size_in_bytes) - 8;
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return BooleanDecoder { move(bit_stream), value, range, bits_left };
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}
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/* 9.2.1 */
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ErrorOr<BooleanDecoder> BooleanDecoder::initialize_vp9(MaybeOwned<BigEndianInputBitStream> bit_stream, size_t size_in_bytes)
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{
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BooleanDecoder decoder = TRY(initialize(move(bit_stream), size_in_bytes));
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if (TRY(decoder.read_bool(128)))
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return Error::from_string_literal("Range decoder marker was non-zero");
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return decoder;
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}
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/* 9.2.2 */
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ErrorOr<bool> BooleanDecoder::read_bool(u8 probability)
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{
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auto split = 1u + (((m_range - 1u) * probability) >> 8u);
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bool return_bool;
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if (m_value < split) {
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m_range = split;
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return_bool = false;
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} else {
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m_range -= split;
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m_value -= split;
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return_bool = true;
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}
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if (m_range < 128) {
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u8 bits_to_shift_into_range = count_leading_zeroes(m_range);
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if (bits_to_shift_into_range > m_bits_left)
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return Error::from_string_literal("Range decoder is out of data");
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m_range <<= bits_to_shift_into_range;
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m_value = (m_value << bits_to_shift_into_range) | TRY(m_bit_stream->read_bits<u8>(bits_to_shift_into_range));
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m_bits_left -= bits_to_shift_into_range;
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}
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return return_bool;
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}
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ErrorOr<u8> BooleanDecoder::read_literal(u8 bits)
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{
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u8 return_value = 0;
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for (size_t i = 0; i < bits; i++) {
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return_value = (2 * return_value) + TRY(read_bool(128));
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}
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return return_value;
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}
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/* 9.2.3 */
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ErrorOr<void> BooleanDecoder::finish_decode_vp9()
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{
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while (m_bits_left > 0) {
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auto padding_read_size = min(m_bits_left, 64);
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auto padding_bits = TRY(m_bit_stream->read_bits(padding_read_size));
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m_bits_left -= padding_read_size;
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if (padding_bits != 0)
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return Error::from_string_literal("Range decoder has non-zero padding element");
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}
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// FIXME: It is a requirement of bitstream conformance that enough padding bits are inserted to ensure that the final coded byte of a frame is not equal to a superframe marker.
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// A byte b is equal to a superframe marker if and only if (b & 0xe0)is equal to 0xc0, i.e. if the most significant 3 bits are equal to 0b110.
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return {};
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}
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}
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