Add TypedArray.from method

This function creates a new way to make TypedArrays based on existing
iterable or Array-like objects, analogous to Array.from. The patch
implements the function and adds tests.

R=arv@chromium.org
BUG=v8:3578
LOG=Y

Review URL: https://codereview.chromium.org/1132163011

Cr-Commit-Position: refs/heads/master@{#28456}

src/harmony-array.js

@@ -6,6 +6,7 @@ var $innerArrayCopyWithin;
 var $innerArrayFill;
 var $innerArrayFind;
 var $innerArrayFindIndex;
+var $arrayFrom;
 
 (function(global, exports) {
 
@@ -254,6 +255,7 @@ function ArrayFrom(arrayLike, mapfn, receiver) {
     return result;
   }
 }
+$arrayFrom = ArrayFrom;
 
 // ES6, draft 05-22-14, section 22.1.2.3
 function ArrayOf() {

src/harmony-typedarray.js

@@ -26,6 +26,7 @@ var GlobalNAME = global.NAME;
 endmacro
 
 TYPED_ARRAYS(DECLARE_GLOBALS)
+DECLARE_GLOBALS(Array)
 
 // -------------------------------------------------------------------
 
@@ -34,7 +35,7 @@ function TypedArrayCopyWithin(target, start, end) {
 
   var length = %_TypedArrayGetLength(this);
 
-  // TODO(dehrenberg): Replace with a memcpy for better performance
+  // TODO(littledan): Replace with a memcpy for better performance
   return $innerArrayCopyWithin(target, start, end, this, length);
 }
 %FunctionSetLength(TypedArrayCopyWithin, 2);
@@ -100,9 +101,35 @@ function TypedArrayOf() {
   return array;
 }
 
+function ConstructTypedArray(constructor, array) {
+  // TODO(littledan): This is an approximation of the spec, which requires
+  // that only real TypedArray classes should be accepted (22.2.2.1.1)
+  if (!IS_SPEC_OBJECT(constructor) || IS_UNDEFINED(constructor.prototype) ||
+      !%HasOwnProperty(constructor.prototype, "BYTES_PER_ELEMENT")) {
+    throw MakeTypeError(kNotTypedArray);
+  }
+
+  // TODO(littledan): The spec requires that, rather than directly calling
+  // the constructor, a TypedArray is created with the proper proto and
+  // underlying size and element size, and elements are put in one by one.
+  // By contrast, this would allow subclasses to make a radically different
+  // constructor with different semantics.
+  return new constructor(array);
+}
+
+function TypedArrayFrom(source, mapfn, thisArg) {
+  // TODO(littledan): Investigate if there is a receiver which could be
+  // faster to accumulate on than Array, e.g., a TypedVector.
+  var array = %_CallFunction(GlobalArray, source, mapfn, thisArg, $arrayFrom);
+  return ConstructTypedArray(this, array);
+}
+%FunctionSetLength(TypedArrayFrom, 1);
+
+// TODO(littledan): Fix the TypedArray proto chain (bug v8:4085).
 macro EXTEND_TYPED_ARRAY(NAME)
   // Set up non-enumerable functions on the object.
   $installFunctions(GlobalNAME, DONT_ENUM | DONT_DELETE | READ_ONLY, [
+    "from", TypedArrayFrom,
     "of", TypedArrayOf
   ]);
 

test/mjsunit/harmony/typedarray-from.js

@@ -0,0 +1,123 @@
+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-arrays
+
+var typedArrayConstructors = [
+  Uint8Array,
+  Int8Array,
+  Uint16Array,
+  Int16Array,
+  Uint32Array,
+  Int32Array,
+  Uint8ClampedArray,
+  Float32Array,
+  Float64Array
+];
+
+for (var constructor of typedArrayConstructors) {
+  assertEquals(1, constructor.from.length);
+
+  // TypedArray.from only callable on this subclassing %TypedArray%
+  assertThrows(function () {constructor.from.call(Array, [])}, TypeError);
+
+  function assertArrayLikeEquals(value, expected, type) {
+    assertEquals(value.__proto__, type.prototype);
+    assertEquals(expected.length, value.length);
+    for (var i = 0; i < value.length; ++i) {
+      assertEquals(expected[i], value[i]);
+    }
+  }
+
+  // Assert that calling mapfn with / without thisArg in sloppy and strict modes
+  // works as expected.
+  var global = this;
+  function non_strict() { assertEquals(global, this); }
+  function strict() { 'use strict'; assertEquals(undefined, this); }
+  function strict_null() { 'use strict'; assertEquals(null, this); }
+  constructor.from([1], non_strict);
+  constructor.from([1], non_strict, void 0);
+  constructor.from([1], non_strict, null);
+  constructor.from([1], strict);
+  constructor.from([1], strict, void 0);
+  constructor.from([1], strict_null, null);
+
+  // TypedArray.from can only be called on TypedArray constructors
+  assertThrows(function() {constructor.from.call({}, [])}, TypeError);
+  assertThrows(function() {constructor.from.call([], [])}, TypeError);
+  assertThrows(function() {constructor.from.call(1, [])}, TypeError);
+  assertThrows(function() {constructor.from.call(undefined, [])}, TypeError);
+
+  // Converting from various other types, demonstrating that it can
+  // operate on array-like objects as well as iterables.
+  // TODO(littledan): constructors should have similar flexibility.
+  assertArrayLikeEquals(constructor.from(
+      { length: 1, 0: 5 }), [5], constructor);
+
+  assertArrayLikeEquals(constructor.from(
+      { length: -1, 0: 5 }), [], constructor);
+
+  assertArrayLikeEquals(constructor.from(
+      [1, 2, 3]), [1, 2, 3], constructor);
+
+  var set = new Set([1, 2, 3]);
+  assertArrayLikeEquals(constructor.from(set), [1, 2, 3],
+        constructor);
+
+  function* generator() {
+    yield 4;
+    yield 5;
+    yield 6;
+  }
+
+  assertArrayLikeEquals(constructor.from(generator()),
+                        [4, 5, 6], constructor);
+
+  assertThrows(function() { constructor.from(null); }, TypeError);
+  assertThrows(function() { constructor.from(undefined); }, TypeError);
+  assertThrows(function() { constructor.from([], null); }, TypeError);
+  assertThrows(function() { constructor.from([], 'noncallable'); },
+               TypeError);
+
+  var nullIterator = {};
+  nullIterator[Symbol.iterator] = null;
+  assertArrayLikeEquals(constructor.from(nullIterator), [],
+                        constructor);
+
+  var nonObjIterator = {};
+  nonObjIterator[Symbol.iterator] = function() { return 'nonObject'; };
+  assertThrows(function() { constructor.from(nonObjIterator); },
+               TypeError);
+
+  assertThrows(function() { constructor.from([], null); }, TypeError);
+
+  // Ensure iterator is only accessed once, and only invoked once
+  var called = 0;
+  var arr = [1, 2, 3];
+  var obj = {};
+  var counter = 0;
+
+  // Test order --- only get iterator method once
+  function testIterator() {
+    called++;
+    assertEquals(obj, this);
+    return arr[Symbol.iterator]();
+  }
+  var getCalled = 0;
+  Object.defineProperty(obj, Symbol.iterator, {
+    get: function() {
+      getCalled++;
+      return testIterator;
+    },
+    set: function() {
+      assertUnreachable('@@iterator should not be set');
+    }
+  });
+  assertArrayLikeEquals(constructor.from(obj), [1, 2, 3], constructor);
+  assertEquals(getCalled, 1);
+  assertEquals(called, 1);
+
+  assertEquals(constructor, Uint8Array.from.call(constructor, [1]).constructor);
+  assertEquals(Uint8Array, constructor.from.call(Uint8Array, [1]).constructor);
+}