From 3586889c03cae00263de98129b1662e9abc7b14a Mon Sep 17 00:00:00 2001
From: Tobi Oetiker <tobi@oetiker.ch>
Date: Tue, 11 Sep 2007 06:12:01 +0000
Subject: rounding error fix for sqrt

---
 CHANGES                     | 2 ++
 lib/Smokeping/RRDhelpers.pm | 3 ++-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/CHANGES b/CHANGES
index e0e2ae8..0b27331 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,5 @@
+* fixed problem with rounding error in calculating stddev
+
 2007/9/06 -- released version 2.2.3
 * alter ajax grapher mode to use seconds timestamps and not iso dates
   this prevents timezone problems with the browser -- tobi
diff --git a/lib/Smokeping/RRDhelpers.pm b/lib/Smokeping/RRDhelpers.pm
index 3f4fa5b..e491a5c 100644
--- a/lib/Smokeping/RRDhelpers.pm
+++ b/lib/Smokeping/RRDhelpers.pm
@@ -52,7 +52,8 @@ sub get_stddev{
         }
     }
     return undef unless $cnt;
-    return sqrt( 1.0 / $cnt * ( $sqsum - $sum**2 / $cnt ))
+    my $sqdev =  1.0 / $cnt * ( $sqsum - $sum**2 / $cnt );
+    return $sqdev < 0.0 ? 0.0 : sqrt($sqdev);
 }
 
 
-- 
cgit v1.2.3-24-g4f1b