add "hamming" function

2 files changed, 23 insertions, 0 deletions

diff --git a/vespajlib/src/main/java/com/yahoo/tensor/Tensor.java b/vespajlib/src/main/java/com/yahoo/tensor/Tensor.java
index ab475e25387..3d4536d9249 100644
--- a/vespajlib/src/main/java/com/yahoo/tensor/Tensor.java
+++ b/vespajlib/src/main/java/com/yahoo/tensor/Tensor.java
@@ -36,6 +36,7 @@ import java.util.function.Function;
 import java.util.stream.Collectors;
 
 import static com.yahoo.text.Ascii7BitMatcher.charsAndNumbers;
+import static com.yahoo.tensor.functions.ScalarFunctions.Hamming;
 
 /**
  * A multidimensional array which can be used in computations.
@@ -241,6 +242,7 @@ public interface Tensor {
     default Tensor notEqual(Tensor argument) { return join(argument, (a, b) -> ( a != b ? 1.0 : 0.0)); }
     default Tensor approxEqual(Tensor argument) { return join(argument, (a, b) -> ( approxEquals(a,b) ? 1.0 : 0.0)); }
     default Tensor bit(Tensor argument) { return join(argument, (a,b) -> ((int)b < 8 && (int)b >= 0 && ((int)a & (1 << (int)b)) != 0) ? 1.0 : 0.0); }
+    default Tensor hamming(Tensor argument) { return join(argument, (a,b) -> Hamming.hamming(a,b)); }
 
     default Tensor avg() { return avg(Collections.emptyList()); }
     default Tensor avg(String dimension) { return avg(Collections.singletonList(dimension)); }
diff --git a/vespajlib/src/main/java/com/yahoo/tensor/functions/ScalarFunctions.java b/vespajlib/src/main/java/com/yahoo/tensor/functions/ScalarFunctions.java
index 3ee9e67cdd6..d6fcd17b8fb 100644
--- a/vespajlib/src/main/java/com/yahoo/tensor/functions/ScalarFunctions.java
+++ b/vespajlib/src/main/java/com/yahoo/tensor/functions/ScalarFunctions.java
@@ -33,6 +33,7 @@ public class ScalarFunctions {
     public static DoubleBinaryOperator pow() { return new Pow(); }
     public static DoubleBinaryOperator squareddifference() { return new SquaredDifference(); }
     public static DoubleBinaryOperator subtract() { return new Subtract(); }
+    public static DoubleBinaryOperator hamming() { return new Hamming(); }
 
     public static DoubleUnaryOperator abs() { return new Abs(); }
     public static DoubleUnaryOperator acos() { return new Acos(); }
@@ -152,6 +153,26 @@ public class ScalarFunctions {
         public String toString() { return "f(a,b)(a - b)"; }
     }
 
+    
+    public static class Hamming implements DoubleBinaryOperator {
+        public static double hamming(double left, double right) {
+            double distance = 0;
+            byte a = (byte) left;
+            byte b = (byte) right;
+            for (int i = 0; i < 8; i++) {
+                byte bit = (byte) (1 << i);
+                if ((a & bit) != (b & bit)) {
+                    distance += 1;
+                }
+            }
+            return distance;
+        }
+        @Override
+        public double applyAsDouble(double left, double right) { return hamming(left, right); }
+        @Override
+        public String toString() { return "f(a,b)(hamming(a,b))"; }
+    }
+
 
     // Unary operators ------------------------------------------------------------------------------