implement reverse

src/lib/validate-input.js

@@ -471,7 +471,10 @@ export function validatePool2dParams(input, _, {roundingType = 'floor'}) {
   }
 }
 
-export function validateReduceParams(input, {axes}) {
+export function validateAxes(input, axes) {
+  if (axes === undefined) {
+    return;
+  }
   if (axes.length > input.rank) {
     throw new Error(`The length ${axes.length} of axes is bigger` +
                     `than input rank ${input.rank}.`);

src/reduce.js

@@ -4,10 +4,10 @@ import {pow} from './binary.js';
 import {squeeze} from './reshape.js';
 import {abs, exp, log} from './unary.js';
 import {sizeOfShape, Scalar, Tensor} from './lib/tensor.js';
-import {validateReduceParams} from './lib/validate-input.js';
+import {validateAxes} from './lib/validate-input.js';
 
 export function selectValuesToReduce(input, axes, inputLocation) {
-  validateReduceParams(input, {axes});
+  validateAxes(input, axes);
 
   const outputShape = input.shape.slice();
   for (let i = 0; i < axes.length; ++i) {

src/reverse.js

@@ -0,0 +1,33 @@
+'use strict';
+
+import {sizeOfShape, Tensor} from './lib/tensor.js';
+import {validateAxes} from './lib/validate-input.js';
+
+/**
+ * Reverse input along the given axes.
+ * @param {Tensor} input
+ * @param {MLReverseOptions} [options]
+ * @return {Tensor}
+ */
+export function reverse(input, {axes}) {
+  validateAxes(input, axes);
+
+  const inputAxes = axes ?? new Array(input.rank).fill(0).map((_, i) => i);
+  const inputShape = input.shape;
+  const outputShape = inputShape.slice();
+  const outputSize = sizeOfShape(outputShape);
+  const output = new Tensor(outputShape);
+
+  for (let outputIndex = 0; outputIndex < outputSize; ++outputIndex) {
+    const outputLocation = output.locationFromIndex(outputIndex);
+    const selectedInputLocation = outputLocation.slice();
+    for (const axis of inputAxes) {
+      const index = selectedInputLocation[axis];
+      selectedInputLocation[axis] = inputShape[axis] - index - 1;
+    }
+    const selectedInputValue = input.getValueByLocation(selectedInputLocation);
+    output.setValueByLocation(outputLocation, selectedInputValue);
+  }
+
+  return output;
+}

test/reverse_test.js

@@ -0,0 +1,65 @@
+'use strict';
+
+import {reverse} from '../src/reverse.js';
+import {Tensor} from '../src/lib/tensor.js';
+import * as utils from './utils.js';
+
+describe('test reverse', function() {
+  function testReverse(inputShape, inputValue, expected, options = {}) {
+    const inputTensor = new Tensor(inputShape, inputValue);
+    const outputTensor = reverse(inputTensor, options);
+    utils.checkShape(outputTensor, inputShape);
+    utils.checkValue(outputTensor, expected);
+  }
+
+  it('reverse 0D scalar default options', function() {
+    testReverse([], [2], [2]);
+  });
+
+  it('reverse 4D default options', function() {
+    testReverse(
+        [2, 2, 2, 2],
+        [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16],
+        [16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1]);
+  });
+
+  it('reverse 2D with axes=[0]', function() {
+    testReverse(
+        [2, 2],
+        [1, 2, 3, 4],
+        [3, 4, 1, 2],
+        {
+          axes: [0],
+        });
+  });
+
+  it('reverse 4D with axes=[3]', function() {
+    testReverse(
+        [2, 2, 2, 2],
+        [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16],
+        [2, 1, 4, 3, 6, 5, 8, 7, 10, 9, 12, 11, 14, 13, 16, 15],
+        {
+          axes: [3],
+        });
+  });
+
+  it('reverse 4D with axes=[1, 2]', function() {
+    testReverse(
+        [2, 2, 2, 2],
+        [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16],
+        [7, 8, 5, 6, 3, 4, 1, 2, 15, 16, 13, 14, 11, 12, 9, 10],
+        {
+          axes: [1, 2],
+        });
+  });
+
+  it('reverse 4D with axes=[3, 1, 0, 2]', function() {
+    testReverse(
+        [2, 2, 2, 2],
+        [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16],
+        [16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1],
+        {
+          axes: [3, 1, 0, 2],
+        });
+  });
+});