#include <math.h>
#include "ringbuf.h"

int ringbuf_init(struct ringbuf *ringbuf, int cap)
{
	if (cap > RINGBUF_MAX_SIZE)
		return -1;

	ringbuf->p = 0;
	ringbuf->full = 0;
	ringbuf->sum = ringbuf->sum2 = 0.0;
	ringbuf->cap = cap;

	return 0;
}

void ringbuf_push(struct ringbuf *ringbuf, float value)
{
	if (ringbuf->full) {
		float old = ringbuf->buf[ringbuf->p];
		ringbuf->sum -= old;
		ringbuf->sum2 -= old * old;
	}

	ringbuf->sum += value;
	ringbuf->sum2 += value * value;

	ringbuf->buf[ringbuf->p++] = value;
	if (ringbuf->p == ringbuf->cap) {
		ringbuf->p = 0;
		ringbuf->full = 1;
	}
}

int ringbuf_size(struct ringbuf *ringbuf)
{
	return ringbuf->full ? ringbuf->cap : ringbuf->p;
}

float ringbuf_mean(struct ringbuf *ringbuf)
{
	int sz = ringbuf_size(ringbuf);
	if (sz == 0)
		return 0;
	return ringbuf->sum / sz;
}

float ringbuf_variance(struct ringbuf *ringbuf)
{
	float mean;
	int sz = ringbuf_size(ringbuf);
	if (sz == 0)
		return 0;

	mean = ringbuf_mean(ringbuf);
	return ringbuf->sum2 / sz - mean * mean;
}

float ringbuf_stdev(struct ringbuf *ringbuf)
{
	return sqrt(ringbuf_variance(ringbuf));
}

/* vim: set ts=8 sw=8 sts=8 noet: */