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allow empty DHT marker #138

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allow empty DHT marker #138

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5cf53f5
allow empty DHT marker
Jun 4, 2025
5c40bd0
fix styling
Jun 4, 2025
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6 changes: 5 additions & 1 deletion lib/jpegli/bitstream.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -192,10 +192,12 @@ void EncodeDHT(j_compress_ptr cinfo, size_t offset, size_t num) {
for (size_t i = 0; i < num; ++i) {
const JHUFF_TBL& table = m->huffman_tables[offset + i];
if (table.sent_table) continue;
marker_len += kJpegHuffmanMaxBitLength + 1;
for (size_t j = 0; j <= kJpegHuffmanMaxBitLength; ++j) {
marker_len += table.bits[j];
}
// Special case: empty DHT markerAdd commentMore actions
if (marker_len == 2) break;
marker_len += kJpegHuffmanMaxBitLength + 1;
}
std::vector<uint8_t> data(marker_len + 2);
size_t pos = 0;
Expand All @@ -210,6 +212,8 @@ void EncodeDHT(j_compress_ptr cinfo, size_t offset, size_t num) {
for (size_t i = 0; i <= kJpegHuffmanMaxBitLength; ++i) {
total_count += table.bits[i];
}
// Special case: empty DHT marker
if (total_count == 0) break;
data[pos++] = m->slot_id_map[offset + t];
for (size_t i = 1; i <= kJpegHuffmanMaxBitLength; ++i) {
data[pos++] = table.bits[i];
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5 changes: 2 additions & 3 deletions lib/jpegli/decode_marker.cc
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Expand Up @@ -284,9 +284,8 @@ void ProcessSOS(j_decompress_ptr cinfo, const uint8_t* data, size_t len) {
// and solt_id of Huffman code being read.
void ProcessDHT(j_decompress_ptr cinfo, const uint8_t* data, size_t len) {
size_t pos = 2;
if (pos == len) {
JPEGLI_ERROR("DHT marker: no Huffman table found");
}
// Empty DHT marker.
if (pos == len) return;
while (pos < len) {
JPEG_VERIFY_LEN(1 + kJpegHuffmanMaxBitLength);
// The index of the Huffman code in the current set of Huffman codes. For AC
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