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LibGfx/JPEG: Use peek_bits in next_symbol

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This allows us to read all bits in a single shot instead of one by one.
This commit is contained in:
Lucas CHOLLET 2023-04-29 15:45:20 -04:00 • committed by Andreas Kling
parent 5ec2aa4dcc
commit f4014f898d
1 changed files with 5 additions and 4 deletions
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9
Userland/Libraries/LibGfx/ImageFormats/JPEGLoader.cpp
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@ -229,15 +229,16 @@ public:
ErrorOr<u8> next_symbol(HuffmanTableSpec const& table) ErrorOr<u8> next_symbol(HuffmanTableSpec const& table)
{ {
unsigned code = 0; u16 const code = peek_bits(16);
u64 code_cursor = 0; u64 code_cursor = 0;
for (int i = 0; i < 16; i++) { // Codes can't be longer than 16 bits. for (int i = 0; i < 16; i++) { // Codes can't be longer than 16 bits.
auto result = TRY(read_bits()); auto const result = code >> (15 - i);
code = (code << 1) | result;
for (int j = 0; j < table.code_counts[i]; j++) { for (int j = 0; j < table.code_counts[i]; j++) {
if (code == table.codes[code_cursor]) if (result == table.codes[code_cursor]) {
discard_bits(i + 1);
return table.symbols[code_cursor]; return table.symbols[code_cursor];
}
code_cursor++; code_cursor++;
} }
} }