kc3-lang/libjpeg-turbo

2021-04-15T22:26:53

Huff dec: Fix non-deterministic output w/bad input Referring to https://bugzilla.mozilla.org/show_bug.cgi?id=1050342, there are certain very rare circumstances under which a malformed JPEG image can cause different Huffman decoder output to be produced, depending on the size of the source manager's I/O buffer. (More specifically, the fast Huffman decoder didn't handle invalid codes in the same manner as the slow decoder, and since the fast decoder requires all data to be memory-resident, the buffering strategy determines whether or not the fast decoder can be used on a particular MCU block.) After extensive experimentation, the Mozilla and Chrome developers and I determined that this truly was an innocuous issue. The patch that both browsers adopted as a workaround caused a performance regression with 32-bit code, which is why it was not accepted into libjpeg-turbo. This commit fixes the problem in a less disruptive way with no performance regression.