def extend(old, newlow, w=8):
    mask = (1<<w)-1
    maxdelta = mask/2
    oldhigh = old & ~mask
    oldlow = old & mask
    if oldlow < newlow:
        candidate1 = oldhigh + newlow
        candidate2 = oldhigh + newlow - (1<<w)
    else:
        candidate1 = oldhigh + newlow
        candidate2 = oldhigh + newlow + (1<<w)

    if abs(old - candidate1) > maxdelta:
        return candidate2
    else:
        return candidate1