mirror of
https://github.com/RGBCube/serenity
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24ae35086d
Errors are now deferred until `finish_decode()` is finished, meaning branches to return errors only need to occur at the end of a ranged decode. If VPX_DEBUG is enabled, a debug message will be printed immediately when an overread occurs. Average decoding times for `Tests/LibGfx/test-inputs/4.webp` improve by about 4.7% with this change, absolute decode times changing from 27.4ms±1.1ms down to 26.1ms±1.0ms.
55 lines
1.4 KiB
C++
55 lines
1.4 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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#pragma once
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#include <AK/BitStream.h>
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#include <AK/Error.h>
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#include <AK/Optional.h>
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#include <AK/Types.h>
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namespace Gfx {
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// Can decode bitstreams encoded with VP8's and VP9's arithmetic boolean encoder.
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class BooleanDecoder {
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public:
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static ErrorOr<BooleanDecoder> initialize(ReadonlyBytes data);
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/* (9.2) */
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bool read_bool(u8 probability);
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u8 read_literal(u8 bits);
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ErrorOr<void> finish_decode();
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private:
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using ValueType = size_t;
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static constexpr u8 reserve_bytes = sizeof(ValueType) - 1;
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static constexpr u8 reserve_bits = reserve_bytes * 8;
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BooleanDecoder(u8 const* data, u64 bytes_left)
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: m_data(data + 1)
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, m_bytes_left(bytes_left - 1)
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, m_range(255)
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, m_value(static_cast<ValueType>(*data) << reserve_bits)
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, m_value_bits_left(8)
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{
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fill_reservoir();
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}
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void fill_reservoir();
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u8 const* m_data;
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size_t m_bytes_left { 0 };
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bool m_overread { false };
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// This value will never exceed 255. If this is a u8, the compiler will generate a truncation in read_bool().
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u32 m_range { 0 };
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ValueType m_value { 0 };
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// Like above, this will never exceed reserve_bits, but will truncate if it is a u8.
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u32 m_value_bits_left { 0 };
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};
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}
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