utils: add rolling_avg

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/utils.c

@@ -164,4 +164,83 @@ TEST_CASE(rolling_max_test) {
 #undef NELEM
 }
 
+/// A rolling average of a stream of integers.
+struct rolling_avg {
+	/// The sum of the elements in the window.
+	int64_t sum;
+
+	/// The elements in the window.
+	int *elem;
+	int head, nelem;
+
+	int window_size;
+};
+
+struct rolling_avg *rolling_avg_new(int size) {
+	auto rm = ccalloc(1, struct rolling_avg);
+	if (!rm) {
+		return NULL;
+	}
+
+	rm->elem = ccalloc(size, int);
+	rm->window_size = size;
+	if (!rm->elem) {
+		free(rm);
+		return NULL;
+	}
+
+	return rm;
+}
+
+void rolling_avg_destroy(struct rolling_avg *rm) {
+	free(rm->elem);
+	free(rm);
+}
+
+void rolling_avg_reset(struct rolling_avg *ra) {
+	ra->sum = 0;
+	ra->nelem = 0;
+	ra->head = 0;
+}
+
+void rolling_avg_push(struct rolling_avg *ra, int val) {
+	if (ra->nelem == ra->window_size) {
+		// Discard the oldest element.
+		// rm->elem.pop_front();
+		ra->sum -= ra->elem[ra->head % ra->window_size];
+		ra->nelem--;
+		ra->head = (ra->head + 1) % ra->window_size;
+	}
+
+	// Add the new element to the queue.
+	// rm->elem.push_back(val)
+	ra->elem[(ra->head + ra->nelem) % ra->window_size] = val;
+	ra->sum += val;
+	ra->nelem++;
+}
+
+double rolling_avg_get_avg(struct rolling_avg *ra) {
+	if (ra->nelem == 0) {
+		return 0;
+	}
+	return (double)ra->sum / (double)ra->nelem;
+}
+
+TEST_CASE(rolling_avg_test) {
+#define NELEM 15
+	auto rm = rolling_avg_new(3);
+	const int data[NELEM] = {1, 2, 3, 1, 4, 5, 2, 3, 6, 5, 4, 3, 2, 0, 0};
+	const double expected_avg[NELEM] = {
+	    1,          1.5,        2, 2, 8.0 / 3.0, 10.0 / 3.0, 11.0 / 3.0, 10.0 / 3.0,
+	    11.0 / 3.0, 14.0 / 3.0, 5, 4, 3,         5.0 / 3.0,  2.0 / 3.0};
+	double avg[NELEM] = {0};
+	for (int i = 0; i < NELEM; i++) {
+		rolling_avg_push(rm, data[i]);
+		avg[i] = rolling_avg_get_avg(rm);
+	}
+	for (int i = 0; i < NELEM; i++) {
+		TEST_EQUAL(avg[i], expected_avg[i]);
+	}
+}
+
 // vim: set noet sw=8 ts=8 :

src/utils.h

@@ -297,6 +297,13 @@ void rolling_max_reset(struct rolling_max *rm);
 void rolling_max_push(struct rolling_max *rm, int val);
 int rolling_max_get_max(struct rolling_max *rm);
 
+struct rolling_avg;
+struct rolling_avg *rolling_avg_new(int window_size);
+void rolling_avg_free(struct rolling_avg *ra);
+void rolling_avg_reset(struct rolling_avg *ra);
+void rolling_avg_push(struct rolling_avg *ra, int val);
+double rolling_avg_get_avg(struct rolling_avg *ra);
+
 // Some versions of the Android libc do not have timespec_get(), use
 // clock_gettime() instead.
 #ifdef __ANDROID__