1 files changed, 40 insertions, 0 deletions
diff --git a/container-search/src/main/java/com/yahoo/search/ranking/RangeAdjuster.java b/container-search/src/main/java/com/yahoo/search/ranking/RangeAdjuster.java
new file mode 100644
index 00000000000..6881eece620
--- /dev/null
+++ b/container-search/src/main/java/com/yahoo/search/ranking/RangeAdjuster.java
@@ -0,0 +1,40 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.search.ranking;
+
+// scale and adjust the score according to the range
+// of the original and final score values to avoid that
+// a score from the backend is larger than finalScores_low
+class RangeAdjuster {
+    private double initialScores_high = -Double.MAX_VALUE;
+    private double initialScores_low = Double.MAX_VALUE;
+    private double finalScores_high = -Double.MAX_VALUE;
+    private double finalScores_low = Double.MAX_VALUE;
+
+    boolean rescaleNeeded() {
+        return (initialScores_low > finalScores_low
+                &&
+                initialScores_high >= initialScores_low
+                &&
+                finalScores_high >= finalScores_low);
+    }
+    void withInitialScore(double score) {
+        if (score < initialScores_low) initialScores_low = score;
+        if (score > initialScores_high) initialScores_high = score;
+    }
+    void withFinalScore(double score) {
+        if (score < finalScores_low) finalScores_low = score;
+        if (score > finalScores_high) finalScores_high = score;
+    }
+    private double initialRange() {
+        double r = initialScores_high - initialScores_low;
+        if (r < 1.0) r = 1.0;
+        return r;
+    }
+    private double finalRange() {
+        double r = finalScores_high - finalScores_low;
+        if (r < 1.0) r = 1.0;
+        return r;
+    }
+    double scale() { return finalRange() / initialRange(); }
+    double bias() { return finalScores_low - initialScores_low * scale(); }
+}