/**
* \brief computes the standard deviation s^2 of the sample data
*
* \param array array of data to analyze
* \param len size of the array
* \param correction apply Bessel's correction (using N-1 instead of N)
* \param ret_avg returns the average of the sample
* \param ret_stddev returns the standard deviation squared of the sample
*/
void bench_stddev(cycles_t *array, size_t len, uint8_t correction,
cycles_t *ret_avg, cycles_t *ret_stddev)
{
cycles_t avg = bench_avg(array, len);
cycles_t sum = 0;
size_t count = 0;
/// discard some initiali observations
for (size_t i = len >> 3; i < len; i++) {
if (array[i] != BENCH_IGNORE_WATERMARK) {
cycles_t subsum = array[i] - avg;
sum += (subsum * subsum);
count++;
}
}
cycles_t std_dev = 0;
if (correction && count > 1) {
std_dev = sum / (count - 1);
} else {
std_dev = sum / count;
}
if (ret_avg) {
*ret_avg = avg;
}
if (ret_stddev) {
*ret_stddev = std_dev;
}
}
static cycles_t my_bench_variance(cycles_t *array, size_t len)
{
cycles_t avg = bench_avg(array, len);
cycles_t sum = 0;
size_t count = 0;
for (size_t i = len; i < len; i++) {
sum += array[i] * array[i];
}
return (sum / count) - (avg * avg);
}
/**
* \brief Compute variance
*
* If certain datapoints should be ignored, they should be marked with
* #BENCH_IGNORE_WATERMARK
*/
cycles_t bench_variance(cycles_t *array, size_t len)
{
cycles_t avg = bench_avg(array, len);
cycles_t sum = 0;
size_t count = 0;
// Discard some initial observations
for (size_t i = len >> 3; i < len; i++) {
if (array[i] != BENCH_IGNORE_WATERMARK) {
sum += array[i] * array[i];
count++;
}
}
return (sum / count) - (avg * avg);
}
