support strides options for slice op

src/lib/validate-input.js

@@ -483,7 +483,7 @@ export function validateReduceParams(input, {axes}) {
   }
 }
 
-export function validateSliceParams(input, starts, sizes) {
+export function validateSliceParams(input, starts, sizes, {strides} = {}) {
   const rank = input.rank;
   if (starts.length !== rank) {
     throw new Error(`The length ${starts.length} of starts is not equal to the length ` +
@@ -493,6 +493,11 @@ export function validateSliceParams(input, starts, sizes) {
     throw new Error(`The length ${sizes.length} of sizes is not equal` +
                     ` to the length ${rank} of input.`);
   }
+  if (strides !== undefined && strides.length !== rank) {
+    throw new Error(`The length ${strides.length} of strides is not equal` +
+                    ` to the length ${rank} of input.`);
+  }
+
   for (let i = 0; i < rank; ++i) {
     const size = input.shape[i];
     const start = starts[i];
@@ -507,6 +512,13 @@ export function validateSliceParams(input, starts, sizes) {
       if (!Number.isInteger(sliceSize) || sliceSize <= 0) {
         throw new Error(`Invalid sizes value ${sliceSize} - it should be an unsigned integer.`);
       }
+      if (strides !== undefined) {
+        const stride = strides[i];
+        if (!Number.isInteger(stride) || stride < 1) {
+          throw new Error(`Invalid strides value ${stride} - it should be an unsigned integer ` +
+                          'greater than or equal to 1.');
+        }
+      }
       if (start + sliceSize > size) {
         throw new Error(`Invalid sizes value ${sliceSize} - the sum of the start ${start} ` +
           `plus the size ${sliceSize} is greater than the dimensional size ${size}`);

src/slice.js

@@ -8,17 +8,25 @@ import {validateSliceParams} from './lib/validate-input.js';
  * @param {Tensor} input
  * @param {Array} starts
  * @param {Array} sizes
+ * @param {MLSliceOptions} options
  * @return {Tensor}
  */
-export function slice(input, starts, sizes) {
+export function slice(input, starts, sizes, {strides} = {}) {
   validateSliceParams(...arguments);
-  const outputShape = sizes;
+  strides = strides ?? new Array(input.rank).fill(1);
+  const outputShape = input.shape.slice();
+
+  for (let dimensionIndex = 0; dimensionIndex < input.rank; ++dimensionIndex) {
+    outputShape[dimensionIndex] = Math.floor(sizes[dimensionIndex] / strides[dimensionIndex]) +
+      Number(sizes[dimensionIndex] % strides[dimensionIndex]);
+  }
+
   const output = new Tensor(outputShape);
   for (let outputIndex = 0; outputIndex < sizeOfShape(outputShape); ++outputIndex) {
     const loc = output.locationFromIndex(outputIndex);
     const selectedInputLoc = loc.slice();
     for (let i = 0; i < loc.length; ++i) {
-      selectedInputLoc[i] = loc[i] + starts[i];
+      selectedInputLoc[i] = starts[i] + loc[i] * strides[i];
     }
     const inputValue = input.getValueByLocation(selectedInputLoc);
     output.setValueByIndex(outputIndex, inputValue);

test/slice_test.js

@@ -5,14 +5,14 @@ import {Tensor} from '../src/lib/tensor.js';
 import * as utils from './utils.js';
 
 describe('test slice', function() {
-  function testSlice(inputShape, inputData, starts, sizes, expectedShape, expected) {
+  function testSlice(inputShape, inputData, starts, sizes, expectedShape, expected, options = {}) {
     const input = new Tensor(inputShape, inputData);
-    const output = slice(input, starts, sizes);
+    const output = slice(input, starts, sizes, options);
     utils.checkShape(output, expectedShape);
     utils.checkValue(output, expected);
   }
 
-  it('slice 1D', function() {
+  it('slice 1D default options', function() {
     const inputShape = [4];
     const inputData = [0, 1, 2, 3];
     const starts = [3];
@@ -22,7 +22,7 @@ describe('test slice', function() {
     testSlice(inputShape, inputData, starts, sizes, expectedShape, expected);
   });
 
-  it('slice 3D', function() {
+  it('slice 3D default options', function() {
     const inputShape = [3, 4, 5];
     const inputData = [
       1.3165863e+00,  4.1239005e-02,  4.6697399e-01,  -6.6145003e-02,
@@ -54,4 +54,36 @@ describe('test slice', function() {
     ];
     testSlice(inputShape, inputData, starts, sizes, expectedShape, expected);
   });
+
+  it('slice 2D with strides=[1, 5]', function() {
+    const inputShape = [3, 20];
+    const inputData = [
+      1.3165863e+00,  4.1239005e-02,  4.6697399e-01,  -6.6145003e-02,
+      -3.7128052e-01, -1.0660021e+00, 7.5784922e-01,  3.5759725e-02,
+      1.9211160e+00,  -8.1603736e-01, 1.1800343e-01,  -1.8293047e+00,
+      -2.1316205e-01, -3.6369815e-01, 6.4205879e-01,  7.1544610e-02,
+      6.8498695e-01,  1.0001093e+00,  -5.6261641e-01, -7.3343945e-01,
+
+      1.6827687e+00,  1.2653192e+00,  5.8872145e-01,  3.1535852e-01,
+      3.5038650e-01,  3.5865438e-01,  -3.6469769e-01, -8.7751287e-01,
+      2.7995768e-01,  -1.6042528e+00, 8.6336482e-01,  -1.7991974e+00,
+      -6.8652731e-01, 1.3729302e-03,  -7.7775210e-01, 1.0199220e-01,
+      4.2299256e-01,  1.1432177e-01,  -5.0116669e-02, 1.5525131e+00,
+
+      -8.7060851e-01, 4.5739245e-01,  1.3543987e-01,  -1.5927458e-02,
+      9.1792661e-01,  -4.5001405e-01, 1.9954188e-01,  -5.1338053e-01,
+      -4.1026011e-01, -1.2718531e+00, 4.2538303e-01,  -1.5449624e-01,
+      -3.4380481e-01, 7.8374326e-01,  1.7837452e+00,  9.6105379e-01,
+      -4.8783422e-01, -9.4987392e-01, -8.8750905e-01, -9.8019439e-01,
+    ];
+    const starts = [1, 4];
+    const sizes = [2, 10];
+    const strides = [1, 3];
+    const expectedShape = [2, 4];
+    const expected = [
+      3.5038650e-01, -8.7751287e-01, 8.6336482e-01, 1.3729302e-03,
+      9.1792661e-01, -5.1338053e-01, 4.2538303e-01, 7.8374326e-01,
+    ];
+    testSlice(inputShape, inputData, starts, sizes, expectedShape, expected, {strides});
+  });
 });