bit_find
has_keys = bit_find(key_bits, 0, BTN_MISC - 1);
has_buttons = bit_find(key_bits, BTN_MISC, BTN_JOYSTICK - 1);
has_lmr = bit_find(key_bits, BTN_LEFT, BTN_MIDDLE);
has_rel_axes = bit_find(rel_bits, 0, REL_MAX);
has_abs_axes = bit_find(abs_bits, 0, ABS_MAX);
has_mt = bit_find(abs_bits, ABS_MT_SLOT, ABS_MAX);