Undefined behavior in fheroes2::Flip()

[oleg-derevenetz]

Preliminary checks

• I've checked that there aren't other open issues on the same topic.
• I've checked that this issue is reproducible on the latest snapshot build.

Platform

macOS

Describe the bug

If output image is single-layer, transformOutY becomes nullptr:

fheroes2/src/engine/image.cpp

Line 2263 in 618cfd9

uint8_t * transformOutY = isOutSingleLayer ? nullptr : out.transform() + offsetOut;

But later transformOutY is subject to arithmetic operations, e.g. here:

fheroes2/src/engine/image.cpp

Line 2295 in 618cfd9

for ( ; imageOutY != imageOutYEnd; imageOutY += widthOut, transformOutY += widthOut, imageInY += widthIn, transformInY += widthIn ) {

which is undefined behavior - you only can add or subtract zero to/from nullptr, and that's all.

The same problem is probably present in other places where single-layer images are processed.

Save file

None needed.

Additional info

Credits: Clang UB Sanitizer.