1 files changed, 43 insertions, 0 deletions
diff --git a/js/src/tests/test262/built-ins/Atomics/compareExchange/expected-return-value.js b/js/src/tests/test262/built-ins/Atomics/compareExchange/expected-return-value.js
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+++ b/js/src/tests/test262/built-ins/Atomics/compareExchange/expected-return-value.js
@@ -0,0 +1,43 @@
+// |reftest| skip-if(!this.hasOwnProperty('Atomics')||!this.hasOwnProperty('SharedArrayBuffer')||(this.hasOwnProperty('getBuildConfiguration')&&getBuildConfiguration('arm64-simulator'))) -- Atomics,SharedArrayBuffer is not enabled unconditionally, ARM64 Simulator cannot emulate atomics
+// Copyright (C) 2018 Rick Waldron.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-atomics.compareExchange
+description: >
+  Atomics.compareExchange returns the value that existed at the
+  index prior to the operation.
+info: |
+  Atomics.compareExchange( typedArray, index, expectedValue, replacementValue )
+
+  ...
+  12. Let compareExchange denote a semantic function of two List of
+      byte values arguments that returns the second argument if the
+      first argument is element-wise equal to expectedBytes.
+  13. Return GetModifySetValueInBuffer(buffer, indexedPosition,
+      elementType, replacement, compareExchange).
+
+
+  GetModifySetValueInBuffer( arrayBuffer,
+    byteIndex, type, value, op [ , isLittleEndian ] )
+
+  ...
+  16. Return RawBytesToNumber(type, rawBytesRead, isLittleEndian).
+
+features: [Atomics, SharedArrayBuffer, TypedArray]
+---*/
+
+const buffer = new SharedArrayBuffer(Int32Array.BYTES_PER_ELEMENT * 4);
+const i32a = new Int32Array(buffer);
+const update = 0b00000001000000001000000010000001;
+
+i32a[0] = update;
+
+assert.sameValue(
+  Atomics.compareExchange(i32a, 0, update, 0),
+  update,
+  'Atomics.compareExchange(i32a, 0, update, 0) returns the value of `update` (0b00000001000000001000000010000001)'
+);
+assert.sameValue(i32a[0], 0, 'The value of i32a[0] is 0');
+
+reportCompare(0, 0);