support negative indices

src/gather_nd.js

@@ -35,7 +35,8 @@ export function gatherND(input, indices) {
     const indicesLocation = indices.locationFromIndex(indicesIndex);
     const indicesArray = [];
     for (let i = 0; i < lastIndicesSize; i++) {
-      indicesArray.push(indices.getValueByIndex(indicesIndex + i));
+      const indicesValue = indices.getValueByIndex(indicesIndex + i);
+      indicesArray.push(indicesValue >= 0 ? indicesValue : inputShape[i] + indicesValue);
     }
     for (let tmpIndex = 0; tmpIndex < tmpTotal; ++tmpIndex) {
       const tmpLocation = tmp.locationFromIndex(tmpIndex);

test/gather_nd_test.js

@@ -85,6 +85,28 @@ describe('test gatherND', function() {
     testGatherND(input, indices, expected);
   });
 
+  it('gatherND 2D inputs when 3D negative indices has leading dimensions', function() {
+    const input = {
+      shape: [2, 2],
+      data: [
+        1, 2,
+        3, 4,
+      ],
+    };
+    const indices = {
+      shape: [2, 1, 1],
+      data: [-1, -2],
+    };
+    const expected = {
+      shape: [2, 1, 2],
+      data: [
+        3, 4,
+        1, 2,
+      ],
+    };
+    testGatherND(input, indices, expected);
+  });
+
   it('gatherND 3D inputs by 2D indices', function() {
     // Refer to Example 3 on https://onnx.ai/onnx/operators/onnx__GatherND.html
     const input = {
@@ -113,6 +135,7 @@ describe('test gatherND', function() {
     testGatherND(input, indices, expected);
   });
 
+
   it('gatherND 3D inputs by 3D indices', function() {
     // Refer to Example 4 on https://onnx.ai/onnx/operators/onnx__GatherND.html
     const input = {