Jeremy Klein acc1ed4358 fix: guard DC writes in JPEGDEC MCU_SKIP path (#2058) ...

EIGHT_BIT_GRAYSCALE decode of a 3-component progressive JPEG calls
JPEGDecodeMCU_P with MCU_SKIP for Cb and Cr after every Y MCU. The
existing safe-pMCU patch redirects the wild pointer to &sMCUs[0] but
leaves the DC store unguarded, so each chroma skip overwrites the
just-decoded Y DC with the chroma DC predictor. Output reads sMCUs[0],
gets the trailing Cr DC (~0), and renders an all-black image.

Add `if (iMCU >= 0)` guards to the two pMCU[0] writes (main DC store and
successive-approximation update). The pointer redirect stays as the AC
wild-pointer defense; the new guards stop the silent corruption at
sMCUs[0]. The two fixes are independent and both required.

fixes the progressive 8bit grayscale jpeg regression in 1.3.0

Did you use AI tools to help write this code? partial

2026-05-19 09:52:29 -04:00

..

0001-redirect-pmcu-on-mcu-skip.patch

fix: guard DC writes in JPEGDEC MCU_SKIP path (#2058)

2026-05-19 09:52:29 -04:00

0002-guard-dc-writes-on-mcu-skip.patch

fix: guard DC writes in JPEGDEC MCU_SKIP path (#2058)

2026-05-19 09:52:29 -04:00