ICE_BITSTR_MASK
return ((ICE_BITSTR_MASK << ice_bit_offset(start)) &
(ICE_BITSTR_MASK >> (ICE_BITSTR_BITS - ice_bit_offset(stop) - 1)));
mask = match ? 0 : ICE_BITSTR_MASK;
mask = match ? ICE_BITSTR_MASK : 0;
test = ~(ICE_BITSTR_MASK << ice_bit_offset(start));