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LibGfx/LibVideo: Check for overreads only at end of a VPX range decode

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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.
This commit is contained in:
Zaggy1024 2023-06-01 19:16:57 -05:00 • committed by Andreas Kling
parent 873b0e9470
commit 24ae35086d
8 changed files with 353 additions and 366 deletions
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8
Userland/Libraries/LibGfx/ImageFormats/BooleanDecoder.h
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@ -20,8 +20,8 @@ public:
static ErrorOr<BooleanDecoder> initialize(ReadonlyBytes data);
/* (9.2) */
ErrorOr<bool> read_bool(u8 probability);
ErrorOr<u8> read_literal(u8 bits);
bool read_bool(u8 probability);
u8 read_literal(u8 bits);
ErrorOr<void> finish_decode();
@ -37,12 +37,14 @@ private:
, m_value(static_cast<ValueType>(*data) << reserve_bits)
, m_value_bits_left(8)
{
fill_reservoir();
}
ErrorOr<void> fill_reservoir();
void fill_reservoir();
u8 const* m_data;
size_t m_bytes_left { 0 };
bool m_overread { false };
// This value will never exceed 255. If this is a u8, the compiler will generate a truncation in read_bool().
u32 m_range { 0 };
ValueType m_value { 0 };