[Atomics] code stubs for atomic operations

test/mjsunit/harmony/atomics.js

 // Copyright 2014 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-sharedarraybuffer
 //
 
 function toRangeWrapped(value) {
   var range = this.max - this.min + 1;
   while (value < this.min) {
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       clearArray(array.buffer);
       var name = Object.prototype.toString.call(array);
       for (var i = 0; i < array.length; ++i) {
         array[i] = 0;
         assertEquals(0, Atomics.load(array, i), name);
         array[i] = 50;
         assertEquals(50, Atomics.load(array, i), name);
       }
     })
   });
+
+  // Test Smi range
+  (function () {
+    var sab = new SharedArrayBuffer(4);
+    var i32 = new Int32Array(sab);
+    var u32 = new Uint32Array(sab);
+
+    function testLoad(signedValue, unsignedValue) {
+      u32[0] = unsignedValue;
+      assertEquals(unsignedValue, Atomics.load(u32, 0));
+      assertEquals(signedValue, Atomics.load(i32, 0));
+    }
+
+    testLoad(0x3fffffff,  0x3fffffff); // 2**30-1 (always smi)
+    testLoad(0x40000000,  0x40000000); // 2**30 (smi if signed and 32-bits)
+    testLoad(0x80000000, -0x80000000); // 2**31 (smi if signed and 32-bits)
+    testLoad(0xffffffff, -1);          // 2**31 (smi if signed)
+  });
 })();
 
 (function TestStore() {
   IntegerTypedArrayConstructors.forEach(function(t) {
     var sab = new SharedArrayBuffer(10 * t.constr.BYTES_PER_ELEMENT);
     var sta = new t.constr(sab);
     var sta2 = new t.constr(sab, 5 * t.constr.BYTES_PER_ELEMENT);
 
     [sta, sta2].forEach(function(array) {
       clearArray(array.buffer);
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       // Exchange
       sta[0] = val = 0x12;
       operand = 0x22 + offset;
       valWrapped = t.toRange(operand);
       assertEquals(val, Atomics.exchange(sta, 0, operand), name);
       assertEquals(valWrapped, sta[0], name);
     }
 
   });
 })();