mrs_field_cmp
if (mrs_field_cmp(new_val, cur, shift, width, sign) == 0)
if (mrs_field_cmp(new_val, cur, shift, width, sign) < 0)
if (mrs_field_cmp(new_val, cur, shift, width, sign) > 0)
if (mrs_field_cmp(reg, min, fields[j].shift,