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LibGfx/JBIG2: Extract read_id() into a class

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We'll need this for refinement/aggregate coding of symbols.
This commit is contained in:
Nico Weber 2024-03-21 11:48:12 -04:00 committed by Tim Flynn
parent 68d47cb84a
commit 3fa2ecdd65
Notes: sideshowbarker 2024-07-17 06:00:02 +09:00 
Author: https://github.com/nico
Commit: https://github.com/SerenityOS/serenity/commit/3fa2ecdd65
Pull-request: https://github.com/SerenityOS/serenity/pull/23710
Reviewed-by: https://github.com/trflynn89 ✅
1 changed files with 34 additions and 13 deletions
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47
Userland/Libraries/LibGfx/ImageFormats/JBIG2Loader.cpp
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@ -290,6 +290,38 @@ Optional<int> ArithmeticIntegerDecoder::decode()
return S ? -V : V;
}
class ArithmeticIntegerIDDecoder {
public:
ArithmeticIntegerIDDecoder(ArithmeticDecoder&, u32 code_length);
// A.3 The IAID decoding procedure
u32 decode();
private:
ArithmeticDecoder& m_decoder;
u32 m_code_length { 0 };
Vector<ArithmeticDecoder::Context> contexts;
};
ArithmeticIntegerIDDecoder::ArithmeticIntegerIDDecoder(ArithmeticDecoder& decoder, u32 code_length)
: m_decoder(decoder)
, m_code_length(code_length)
{
contexts.resize(1 << (code_length + 1));
}
u32 ArithmeticIntegerIDDecoder::decode()
{
// A.3 The IAID decoding procedure
u32 prev = 1;
for (u8 i = 0; i < m_code_length; ++i) {
bool bit = m_decoder.get_next_bit(contexts[prev]);
prev = (prev << 1) | bit;
}
prev = prev - (1 << m_code_length);
return prev;
}
}
static u8 number_of_context_bits_for_template(u8 template_)
@ -1191,18 +1223,7 @@ static ErrorOr<NonnullOwnPtr<BitBuffer>> text_region_decoding_procedure(TextRegi
// If SBHUFF is 0, decode a value using the IAID integer arithmetic decoding procedure (see Annex A). Set IDI to the
// resulting value.""
// FIXME: Implement support for SBHUFF = 1.
Vector<JBIG2::ArithmeticDecoder::Context> id_contexts;
id_contexts.resize(1 << (inputs.id_symbol_code_length + 1));
auto read_id = [&]() -> u32 {
// A.3 The IAID decoding procedure
u32 prev = 1;
for (u8 i = 0; i < inputs.id_symbol_code_length; ++i) {
bool bit = decoder.get_next_bit(id_contexts[prev]);
prev = (prev << 1) | bit;
}
prev = prev - (1 << inputs.id_symbol_code_length);
return prev;
};
JBIG2::ArithmeticIntegerIDDecoder id_decoder(decoder, inputs.id_symbol_code_length);
// 6.4.11.1 Symbol instance refinement delta width
// FIXME: Implement support for SBHUFF = 1.
@ -1336,7 +1357,7 @@ static ErrorOr<NonnullOwnPtr<BitBuffer>> text_region_decoding_procedure(TextRegi
i32 t_instance = strip_t + cur_t;
// "iv) Decode the symbol instance's symbol ID as described in 6.4.10. Let IDI be the decoded value."
u32 id = read_id();
u32 id = id_decoder.decode();
// "v) Determine the symbol instance's bitmap IBI as described in 6.4.11. The width and height of this
// bitmap shall be denoted as WI and HI respectively."