Add a class for assist efficient traversal of dimensions in an IndexedTensor.

4 files changed, 91 insertions, 0 deletions

diff --git a/vespajlib/abi-spec.json b/vespajlib/abi-spec.json
index 5d88b2d2829..5b03c8b5661 100644
--- a/vespajlib/abi-spec.json
+++ b/vespajlib/abi-spec.json
@@ -720,6 +720,20 @@
     ],
     "fields" : [ ]
   },
+  "com.yahoo.tensor.DirectIndexedAddress" : {
+    "superClass" : "java.lang.Object",
+    "interfaces" : [ ],
+    "attributes" : [
+      "public",
+      "final"
+    ],
+    "methods" : [
+      "public void setIndex(int, int)",
+      "public long getIndex()",
+      "public long getStride(int)"
+    ],
+    "fields" : [ ]
+  },
   "com.yahoo.tensor.IndexedDoubleTensor$BoundDoubleBuilder" : {
     "superClass" : "com.yahoo.tensor.IndexedTensor$BoundBuilder",
     "interfaces" : [ ],
@@ -894,6 +908,8 @@
       "public java.util.Iterator subspaceIterator(java.util.Set, com.yahoo.tensor.DimensionSizes)",
       "public java.util.Iterator subspaceIterator(java.util.Set)",
       "public varargs double get(long[])",
+      "public double get(com.yahoo.tensor.DirectIndexedAddress)",
+      "public com.yahoo.tensor.DirectIndexedAddress directAddress()",
       "public varargs float getFloat(long[])",
       "public double get(com.yahoo.tensor.TensorAddress)",
       "public boolean has(com.yahoo.tensor.TensorAddress)",
diff --git a/vespajlib/src/main/java/com/yahoo/tensor/DirectIndexedAddress.java b/vespajlib/src/main/java/com/yahoo/tensor/DirectIndexedAddress.java
new file mode 100644
index 00000000000..80cb545238c
--- /dev/null
+++ b/vespajlib/src/main/java/com/yahoo/tensor/DirectIndexedAddress.java
@@ -0,0 +1,38 @@
+package com.yahoo.tensor;
+
+/**
+ * Utility class for efficient access and iteration along dimensions in Indexed tensors.
+ * Usage: Use setIndex to lock the indexes of the dimensions that don't change in this iteration.
+ *        long base = addr.getIndex();
+ *        long stride = addr.getStride(dimension)
+ *        i = 0...size_of_dimension
+ *            double value = tensor.get(base + i * stride);
+ */
+public final class DirectIndexedAddress {
+    private final DimensionSizes sizes;
+    private final int [] indexes;
+    private long directIndex;
+    private DirectIndexedAddress(DimensionSizes sizes) {
+        this.sizes = sizes;
+        indexes = new int[sizes.dimensions()];
+        directIndex = 0;
+    }
+    static DirectIndexedAddress of(DimensionSizes sizes) {
+        return new DirectIndexedAddress(sizes);
+    }
+    /** Sets the current index of a dimension */
+    public void setIndex(int dimension, int index) {
+        if (index < 0 || index >= sizes.size(dimension)) {
+            throw new IndexOutOfBoundsException("Index " + index + " outside of [0," + sizes.size(dimension) + ">");
+        }
+        int diff = index - indexes[dimension];
+        directIndex += getStride(dimension) * diff;
+        indexes[dimension] = index;
+    }
+    /** Retrieve the index that can be used for direct lookup in an indexed tensor. */
+    public long getIndex() { return directIndex; }
+    /** returns the stride to be used for the given dimension */
+    public long getStride(int dimension) {
+        return sizes.productOfDimensionsAfter(dimension);
+    }
+}
diff --git a/vespajlib/src/main/java/com/yahoo/tensor/IndexedTensor.java b/vespajlib/src/main/java/com/yahoo/tensor/IndexedTensor.java
index 1319675f5d4..d43b4a03f72 100644
--- a/vespajlib/src/main/java/com/yahoo/tensor/IndexedTensor.java
+++ b/vespajlib/src/main/java/com/yahoo/tensor/IndexedTensor.java
@@ -93,6 +93,10 @@ public abstract class IndexedTensor implements Tensor {
         return get(toValueIndex(indexes, dimensionSizes));
     }
 
+    public double get(DirectIndexedAddress address) {
+        return get(address.getIndex());
+    }
+    public DirectIndexedAddress directAddress() { return DirectIndexedAddress.of(dimensionSizes); }
     /**
      * Returns the value at the given indexes as a float
      *
diff --git a/vespajlib/src/test/java/com/yahoo/tensor/IndexedTensorTestCase.java b/vespajlib/src/test/java/com/yahoo/tensor/IndexedTensorTestCase.java
index 0a6c821e64e..d145ad7a316 100644
--- a/vespajlib/src/test/java/com/yahoo/tensor/IndexedTensorTestCase.java
+++ b/vespajlib/src/test/java/com/yahoo/tensor/IndexedTensorTestCase.java
@@ -9,6 +9,7 @@ import java.util.Iterator;
 import java.util.Map;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
@@ -96,6 +97,38 @@ public class IndexedTensorTestCase {
     }
 
     @Test
+    public void testDirectIndexedAddress() {
+        TensorType type = new TensorType.Builder().indexed("v", 3)
+                .indexed("w", wSize)
+                .indexed("x", xSize)
+                .indexed("y", ySize)
+                .indexed("z", zSize)
+                .build();
+        var directAddress = DirectIndexedAddress.of(DimensionSizes.of(type));
+        assertThrows(ArrayIndexOutOfBoundsException.class, () -> directAddress.getStride(5));
+        assertThrows(IndexOutOfBoundsException.class, () -> directAddress.setIndex(4, 7));
+        assertEquals(wSize*xSize*ySize*zSize, directAddress.getStride(0));
+        assertEquals(xSize*ySize*zSize, directAddress.getStride(1));
+        assertEquals(ySize*zSize, directAddress.getStride(2));
+        assertEquals(zSize, directAddress.getStride(3));
+        assertEquals(1, directAddress.getStride(4));
+        assertEquals(0, directAddress.getIndex());
+        directAddress.setIndex(0,1);
+        assertEquals(1 * directAddress.getStride(0), directAddress.getIndex());
+        directAddress.setIndex(1,1);
+        assertEquals(1 * directAddress.getStride(0) + 1 * directAddress.getStride(1), directAddress.getIndex());
+        directAddress.setIndex(2,2);
+        directAddress.setIndex(3,2);
+        directAddress.setIndex(4,2);
+        long expected = 1 * directAddress.getStride(0) +
+                1 * directAddress.getStride(1) +
+                2 * directAddress.getStride(2) +
+                2 * directAddress.getStride(3) +
+                2 * directAddress.getStride(4);
+        assertEquals(expected, directAddress.getIndex());
+    }
+
+    @Test
     public void testUnboundBuilding() {
         TensorType type = new TensorType.Builder().indexed("w")
                                                   .indexed("v")