diff -r 000000000000 -r 6474c204b198 js/src/builtin/ParallelUtilities.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/builtin/ParallelUtilities.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,72 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// Shared utility functions for and macros parallel operations in `Array.js`
+// and `TypedObject.js`.
+
+#ifdef ENABLE_PARALLEL_JS
+
+/* The mode asserts options object. */
+#define TRY_PARALLEL(MODE) \
+  ((!MODE || MODE.mode !== "seq"))
+#define ASSERT_SEQUENTIAL_IS_OK(MODE) \
+  do { if (MODE) AssertSequentialIsOK(MODE) } while(false)
+
+/**
+ * The ParallelSpew intrinsic is only defined in debug mode, so define a dummy
+ * if debug is not on.
+ */
+#ifndef DEBUG
+#define ParallelSpew(args)
+#endif
+
+#define MAX_SLICE_SHIFT 6
+#define MAX_SLICE_SIZE 64
+#define MAX_SLICES_PER_WORKER 8
+
+/**
+ * Macros to help compute the start and end indices of slices based on id. Use
+ * with the object returned by ComputeSliceInfo.
+ */
+#define SLICE_START_INDEX(shift, id) \
+    (id << shift)
+#define SLICE_END_INDEX(shift, start, length) \
+    std_Math_min(start + (1 << shift), length)
+
+/**
+ * ForkJoinGetSlice acts as identity when we are not in a parallel section, so
+ * pass in the next sequential value when we are in sequential mode. The
+ * reason for this odd API is because intrinsics *need* to be called during
+ * ForkJoin's warmup to fill the TI info.
+ */
+#define GET_SLICE(sliceStart, sliceEnd, id) \
+    ((id = ForkJoinGetSlice((InParallelSection() ? -1 : sliceStart++) | 0)) < sliceEnd)
+
+/**
+ * Determine the number and size of slices. The info object has the following
+ * properties:
+ *
+ *  - shift: amount to shift by to compute indices
+ *  - count: number of slices
+ */
+function ComputeSlicesInfo(length) {
+  var count = length >>> MAX_SLICE_SHIFT;
+  var numWorkers = ForkJoinNumWorkers();
+  if (count < numWorkers)
+    count = numWorkers;
+  else if (count >= numWorkers * MAX_SLICES_PER_WORKER)
+    count = numWorkers * MAX_SLICES_PER_WORKER;
+
+  // Round the slice size to be a power of 2.
+  var shift = std_Math_max(std_Math_log2(length / count) | 0, 1);
+
+  // Recompute count with the rounded size.
+  count = length >>> shift;
+  if (count << shift !== length)
+    count += 1;
+
+  return { shift: shift, count: count };
+}
+
+#endif // ENABLE_PARALLEL_JS