[Git][wine/wine][master] 2 commits: windowscodecs: Fix decoding GIFs that fill the LZW code table.

[Alexandre Julliard (＠julliard)]

Alexandre Julliard pushed to branch master at wine / wine


Commits:
89b35d3f by Marius Kamm at 2026-06-22T18:50:30+02:00
windowscodecs: Fix decoding GIFs that fill the LZW code table.

The GIF LZW decompressor writes a new table entry at index RunningCode-2
for every code while LastCode != NO_SUCH_CODE. Once the table is full,
DGifDecompressInput freezes RunningCode at LZ_MAX_CODE+2, so
RunningCode-2 stays at 4095 and every subsequent code overwrites the
already-valid entry 4095. For a GIF that fills the 4096-entry table and
keeps emitting codes before a clear code, a later code whose prefix
chain runs through the corrupted entry then produces CrntPrefix >
LZ_MAX_CODE / j >= LZ_MAX_CODE, so DGifDecompressLine returns GIF_ERROR
and the whole image fails to load. Native Windows decodes such files
correctly.

Only define a table entry while it is still empty, matching giflib,
which keeps the full table intact until a clear code arrives.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=59887

- - - - -
c7929af7 by Marius Kamm at 2026-06-22T18:50:30+02:00
windowscodecs/tests: Test decoding a GIF that fills the LZW code table.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=59887

- - - - -


2 changed files:

- dlls/windowscodecs/tests/gifformat.c
- dlls/windowscodecs/ungif.c


View it on GitLab: https://gitlab.winehq.org/wine/wine/-/compare/84f282bd2ada40944dce73ded25610...

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View it on GitLab: https://gitlab.winehq.org/wine/wine/-/compare/84f282bd2ada40944dce73ded25610...
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