EdgePixelCombine

EdgePixelCombine:
                ;b=ABC00000
                ;a=DXE00000
                ;c=FGH00000
    xor b
    and %10111111
    xor b       ;a=DBE00000
    rlca
    rlca            ;a=00DBE000
    xor c
    and %10111111
    xor c       ;a=0GDBE000
    rrca
    rrca            ;a=000GDBE0
    or  b       ;a=ABCGDBE0
    rrca            ;a=0ABCGDBE
    xor c
    and %01011111
    xor c       ;a=FAHCGDBE
    ret