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LibCompress: Handle arbitrarily long FF-chains in the LZMA encoder

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This commit is contained in:
Tim Schumacher 2023-05-19 01:27:31 +02:00 • committed by Jelle Raaijmakers
parent cb93186350
commit a01968ee6d
3 changed files with 76 additions and 29 deletions
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8
Userland/Libraries/LibCompress/Lzma.h
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@ -225,6 +225,7 @@ public:
private:
LzmaCompressor(MaybeOwned<Stream>, LzmaCompressorOptions, MaybeOwned<CircularBuffer>, FixedArray<Probability> literal_probabilities);
ErrorOr<void> shift_range_encoder();
ErrorOr<void> normalize_range_encoder();
ErrorOr<void> encode_direct_bit(u8 value);
ErrorOr<void> encode_bit_with_probability(Probability&, u8 value);
@ -253,7 +254,12 @@ private:
// Range encoder state.
u32 m_range_encoder_range { 0xFFFFFFFF };
u64 m_range_encoder_code { 0 };
size_t m_range_encoder_code_used_bits { 32 };
// Since the range is only 32-bits, we can overflow at most +1 into the next byte beyond the usual 32-bit code.
// Therefore, it is sufficient to store the highest byte (which may still change due to that +1 overflow) and
// the length of the chain of 0xFF bytes that may end up propagating that change.
u8 m_range_encoder_cached_byte { 0x00 };
size_t m_range_encoder_ff_chain_length { 0 };
};
}