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756a8fa02d
...and make it an Array while at it. (This makes it look a little less like the spec, but that seems worth it.) No behavior change.
64 lines
2.1 KiB
C++
64 lines
2.1 KiB
C++
/*
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* Copyright (c) 2024, Nico Weber <thakis@chromium.org>
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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 <LibCompress/Deflate.h>
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namespace Gfx {
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constexpr Array kCodeLengthCodeOrder = { 17, 18, 0, 1, 2, 3, 4, 5, 16, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 };
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// WebP-lossless's CanonicalCodes are almost identical to deflate's.
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// One difference is that codes with a single element in webp-lossless consume 0 bits to produce that single element,
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// while they consume 1 bit in Compress::CanonicalCode. This class wraps Compress::CanonicalCode to handle the case
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// where the codes contain just a single element, and dispatches to Compress::CanonicalCode else.
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class CanonicalCode {
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public:
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CanonicalCode() = default;
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static ErrorOr<CanonicalCode> from_bytes(ReadonlyBytes);
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ErrorOr<u32> read_symbol(LittleEndianInputBitStream&) const;
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ErrorOr<void> write_symbol(LittleEndianOutputBitStream&, u32) const;
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private:
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explicit CanonicalCode(u32 single_symbol)
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: m_code(single_symbol)
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{
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}
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explicit CanonicalCode(Compress::CanonicalCode code)
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: m_code(move(code))
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{
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}
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Variant<u32, Compress::CanonicalCode> m_code { 0 };
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};
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ALWAYS_INLINE ErrorOr<void> CanonicalCode::write_symbol(LittleEndianOutputBitStream& bit_stream, u32 symbol) const
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{
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TRY(m_code.visit(
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[&](u32 single_code) __attribute__((always_inline))->ErrorOr<void> { VERIFY(symbol == single_code); return {}; },
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[&](Compress::CanonicalCode const& code) __attribute__((always_inline)) { return code.write_symbol(bit_stream, symbol); }));
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return {};
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}
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// https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification#61_overview
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// "From here on, we refer to this set as a prefix code group."
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class PrefixCodeGroup {
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public:
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PrefixCodeGroup() = default;
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PrefixCodeGroup(PrefixCodeGroup&&) = default;
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PrefixCodeGroup(PrefixCodeGroup const&) = delete;
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CanonicalCode& operator[](int i) { return m_codes[i]; }
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CanonicalCode const& operator[](int i) const { return m_codes[i]; }
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private:
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Array<CanonicalCode, 5> m_codes;
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};
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}
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