.

vendor/github.com/andybalholm/brotli/cluster.go

@@ -0,0 +1,30 @@
+package brotli
+
+/* Copyright 2013 Google Inc. All Rights Reserved.
+
+   Distributed under MIT license.
+   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+*/
+
+/* Functions for clustering similar histograms together. */
+
+type histogramPair struct {
+	idx1       uint32
+	idx2       uint32
+	cost_combo float64
+	cost_diff  float64
+}
+
+func histogramPairIsLess(p1 *histogramPair, p2 *histogramPair) bool {
+	if p1.cost_diff != p2.cost_diff {
+		return p1.cost_diff > p2.cost_diff
+	}
+
+	return (p1.idx2 - p1.idx1) > (p2.idx2 - p2.idx1)
+}
+
+/* Returns entropy reduction of the context map when we combine two clusters. */
+func clusterCostDiff(size_a uint, size_b uint) float64 {
+	var size_c uint = size_a + size_b
+	return float64(size_a)*fastLog2(size_a) + float64(size_b)*fastLog2(size_b) - float64(size_c)*fastLog2(size_c)
+}