32bit movingAverage with 16bit buffer + offsets - for slowly moving signals

movingAverage.c

#define AVG_WINDOW 16U
static int32_t errMovingAverage(int32_t val) {
	const uint8_t window_n = AVG_WINDOW;
	static int16_t ringbuffer[AVG_WINDOW-1U];
	static int32_t offset = 0;
	static int32_t old_offset = 0;
	
	static uint8_t ringbuffer_idx = window_n-1U;

	static int32_t avg=0;
	static int32_t accu=0;
	
	if (ringbuffer_idx==(window_n-1U)){
		old_offset = offset;
		offset = val;
	}else{
		int16_t delta = (int16_t)(val - offset);
		accu += (int32_t)(delta - (ringbuffer[ringbuffer_idx]));
		ringbuffer[ringbuffer_idx] = delta;
	}

	avg = offset + (accu - ((offset - old_offset)*(int8_t)(uint8_t)(window_n-ringbuffer_idx-1U)))/(int32_t)window_n;
	ringbuffer_idx = (ringbuffer_idx + 1U) % window_n;

	return avg;
}