HID: input: simplify/fix high-res scroll event handling

void hid_scroll_counter_handle_scroll(struct hid_scroll_counter *counter,

				      int hi_res_value)

{

	int low_res_scroll_amount;

	/* Some wheels will rest 7/8ths of a notch from the previous notch

	 * after slow movement, so we want the threshold for low-res events to

	 * be in the middle of the notches (e.g. after 4/8ths) as opposed to on

	 * the notches themselves (8/8ths).

	 */

	int threshold = counter->resolution_multiplier / 2;

	int low_res_value, remainder, multiplier;

	input_report_rel(counter->dev, REL_WHEEL_HI_RES,

			 hi_res_value * counter->microns_per_hi_res_unit);

	counter->remainder += hi_res_value;

	if (abs(counter->remainder) >= threshold) {

		/* Add (or subtract) 1 because we want to trigger when the wheel

		 * is half-way to the next notch (i.e. scroll 1 notch after a

		 * 1/2 notch movement, 2 notches after a 1 1/2 notch movement,

		 * etc.).

	/*

	 * Update the low-res remainder with the high-res value,

	 * but reset if the direction has changed.

	 */

		low_res_scroll_amount =

			counter->remainder / counter->resolution_multiplier

			+ (hi_res_value > 0 ? 1 : -1);

		input_report_rel(counter->dev, REL_WHEEL,

				 low_res_scroll_amount);

		counter->remainder -=

			low_res_scroll_amount * counter->resolution_multiplier;

	}

	remainder = counter->remainder;

	if ((remainder ^ hi_res_value) < 0)

		remainder = 0;

	remainder += hi_res_value;

	/*

	 * Then just use the resolution multiplier to see if

	 * we should send a low-res (aka regular wheel) event.

	 */

	multiplier = counter->resolution_multiplier;

	low_res_value = remainder / multiplier;

	remainder -= low_res_value * multiplier;

	counter->remainder = remainder;

	if (low_res_value)

		input_report_rel(counter->dev, REL_WHEEL, low_res_value);

}

EXPORT_SYMBOL_GPL(hid_scroll_counter_handle_scroll);