Without a doubt, a rather useful function, but why is it internal to the
library code? I can only assume that marking it as static and inline
eeks that extra nanosecond of speed out the library, but then again,
it’s only called from two places within the whole library: SD_FillRect()
and SDL_SetClipRect() neither of which I would have though would have
benefited much from an 'inline’d function.

Perhaps this function could be made public or do we end going down
Microsoft’s ‘code-bloat’ road?–
Alan McFarlane