From: Andre Noll <maan@tuebingen.mpg.de>
Date: Tue, 15 Mar 2016 19:48:12 +0000 (+0100)
Subject: mood.c: Avoid integer underflow.
X-Git-Tag: v0.5.6~45^2~4
X-Git-Url: http://git.tuebingen.mpg.de/?a=commitdiff_plain;h=a37f31bbe4f1b2745ef0f617cff122a2c5f95078;hp=58566e1535a0c47ce59570598885ccabc75891bf;p=paraslash.git

mood.c: Avoid integer underflow.

The three variables x, s, n are all of unsigned type, and the
subtraction x - s / n may underflow, resulting in a very large positive
value. This should not matter since we square the difference, but on
the other hand, the underflow can easily be avoided. This patch uses
a temporary variable to do so.
---

diff --git a/mood.c b/mood.c
index e026c960..415e1702 100644
--- a/mood.c
+++ b/mood.c
@@ -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;