X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=blobdiff_plain;f=mood.c;h=45b051a7267cdd9cd1a9049a00685a150681a1cb;hp=8e6a7665f15e32bc5774c5539358ccaf0bcbc880;hb=985ba0546ab18eadf73d0a2686029a3ac876c846;hpb=1565acea5e9fe7413831c3a49032f35f721de608

diff --git a/mood.c b/mood.c
index 8e6a7665..45b051a7 100644
--- a/mood.c
+++ b/mood.c
@@ -472,7 +472,7 @@ static int64_t normalized_value(int64_t x, int64_t n, int64_t sum, int64_t qd)
 {
 	if (!n || !qd)
 		return 0;
-	return 100 * (n * x - sum) / (int64_t)int_sqrt(n * qd);
+	return 100 * (n * x - sum) / (int64_t)int_sqrt(n) / (int64_t)int_sqrt(qd);
 }
 
 static long compute_num_played_score(struct afs_info *afsi)
@@ -504,7 +504,7 @@ static long compute_dynamic_score(const struct osl_row *aft_row)
 
 static int add_afs_statistics(const struct osl_row *row)
 {
-	uint64_t n, x, s;
+	uint64_t n, x, s, q;
 	struct afs_info afsi;
 	int ret;
 
@@ -514,14 +514,18 @@ static int add_afs_statistics(const struct osl_row *row)
 	n = statistics.num;
 	x = afsi.last_played;
 	s = statistics.last_played_sum;
-	if (n > 0)
-		statistics.last_played_qd += (x - s / n) * (x - s / n) * n / (n + 1);
+	if (n > 0) {
+		q = (x > s / n)? x - s / n : s / n - x;
+		statistics.last_played_qd += q * q * n / (n + 1);
+	}
 	statistics.last_played_sum += x;
 
 	x = afsi.num_played;
 	s = statistics.num_played_sum;
-	if (n > 0)
-		statistics.num_played_qd += (x - s / n) * (x - s / n) * n / (n + 1);
+	if (n > 0) {
+		q = (x > s / n)? x - s / n : s / n - x;
+		statistics.num_played_qd += q * q * n / (n + 1);
+	}
 	statistics.num_played_sum += x;
 	statistics.num++;
 	return 1;
@@ -648,7 +652,8 @@ static int add_if_admissible(struct osl_row *aft_row, void *data)
  * the last number a_n was replaced by b) may be computed in O(1) time in terms
  * of n, q, a_n, b, and S as
  *
- * 	q' = q + d * s - (2 * S + d) * d / n,
+ * 	q' = q + d * s - (2 * S + d) * d / n
+ *	   = q + d * (s - 2 * S / n - d /n),
  *
  * where d = b - a_n, and s = b + a_n.
  *
@@ -665,7 +670,7 @@ _static_inline_ int64_t update_quadratic_deviation(int64_t n, int64_t old_qd,
 {
 	int64_t delta = new_val - old_val;
 	int64_t sigma = new_val + old_val;
-	return old_qd + delta * sigma - (2 * old_sum + delta) * delta / n;
+	return old_qd + delta * (sigma - 2 * old_sum / n - delta / n);
 }
 
 static int update_afs_statistics(struct afs_info *old_afsi, struct afs_info *new_afsi)