MIRROR_VERTICAL only works if y < 8

[city41]

Using ArdBitmap 2.0.3

I find if y goes to 8 or above, then the vertically mirrored sprite gets corrupted. In this program pressing up/down changes y, and the number printed on the screen is the current y:

y=7, no problem

at y=8, the sprite gets halfway corrupted.

at y=16 and above, the sprite gets fully corrupted. The corruption changes with every multiple of 8 on y.

The corruption occurs in the ProjectABE emulator and also on a real ArduBoy.

Here is the program:
https://gist.github.com/city41/14f5eb8c15a131f128b62ebddde950c5

Fix to the problem

I found in ArdBitmap.h, if I remove the else statement here, then the problem goes away. So change this:

  if (mirror & MIRROR_VERTICAL) {
    bofs += (loop_h - 1) * w;
    if (y < 0){
      bofs -=  (start_h * w);
    } else {
      bofs +=  (sRow  * w);
    }
  }

to this:

  if (mirror & MIRROR_VERTICAL) {
    bofs += (loop_h - 1) * w;
    if (y < 0){
      bofs -=  (start_h * w);
    }
  }

I have tested this change with sprites of various sizes and all values for y and have not found a problem.