diff --git a/vendor/github.com/petar/GoLLRB/llrb/avgvar.go b/vendor/github.com/petar/GoLLRB/llrb/avgvar.go
new file mode 100644
index 0000000..2d7e2a3
--- /dev/null
+++ b/vendor/github.com/petar/GoLLRB/llrb/avgvar.go
@@ -0,0 +1,39 @@
+// Copyright 2010 Petar Maymounkov. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package llrb
+
+import "math"
+
+// avgVar maintains the average and variance of a stream of numbers
+// in a space-efficient manner.
+type avgVar struct {
+	count      int64
+	sum, sumsq float64
+}
+
+func (av *avgVar) Init() {
+	av.count = 0
+	av.sum = 0.0
+	av.sumsq = 0.0
+}
+
+func (av *avgVar) Add(sample float64) {
+	av.count++
+	av.sum += sample
+	av.sumsq += sample * sample
+}
+
+func (av *avgVar) GetCount() int64 { return av.count }
+
+func (av *avgVar) GetAvg() float64 { return av.sum / float64(av.count) }
+
+func (av *avgVar) GetTotal() float64 { return av.sum }
+
+func (av *avgVar) GetVar() float64 {
+	a := av.GetAvg()
+	return av.sumsq/float64(av.count) - a*a
+}
+
+func (av *avgVar) GetStdDev() float64 { return math.Sqrt(av.GetVar()) }