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diff --git a/js/public/Equality.h b/js/public/Equality.h
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+++ b/js/public/Equality.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+/* Equality operations. */
+
+#ifndef js_Equality_h
+#define js_Equality_h
+
+#include "mozilla/FloatingPoint.h"
+
+#include "jstypes.h"  // JS_PUBLIC_API
+
+#include "js/RootingAPI.h" // JS::Handle
+#include "js/Value.h"      // JS::Value
+
+struct JSContext;
+
+namespace JS {
+
+/**
+ * Store |v1 === v2| to |*equal| -- strict equality, which performs no
+ * conversions on |v1| or |v2| before comparing.
+ *
+ * This operation can fail only if an internal error occurs (e.g. OOM while
+ * linearizing a string value).
+ */
+extern JS_PUBLIC_API(bool)
+StrictlyEqual(JSContext* cx, JS::Handle<JS::Value> v1, JS::Handle<JS::Value> v2, bool* equal);
+
+/**
+ * Store |v1 == v2| to |*equal| -- loose equality, which may perform
+ * user-modifiable conversions on |v1| or |v2|.
+ *
+ * This operation can fail if a user-modifiable conversion fails *or* if an
+ * internal error occurs. (e.g. OOM while linearizing a string value).
+ */
+extern JS_PUBLIC_API(bool)
+LooselyEqual(JSContext* cx, JS::Handle<JS::Value> v1, JS::Handle<JS::Value> v2, bool* equal);
+
+/**
+ * Stores |SameValue(v1, v2)| to |*equal| -- using the SameValue operation
+ * defined in ECMAScript, initially exposed to script as |Object.is|.  SameValue
+ * behaves identically to strict equality, except that it equates two NaN values
+ * and does not equate differently-signed zeroes.  It performs no conversions on
+ * |v1| or |v2| before comparing.
+ *
+ * This operation can fail only if an internal error occurs (e.g. OOM while
+ * linearizing a string value).
+ */
+extern JS_PUBLIC_API(bool)
+SameValue(JSContext* cx, JS::Handle<JS::Value> v1, JS::Handle<JS::Value> v2, bool* same);
+
+/**
+ * Implements |SameValueZero(v1, v2)| for Number values |v1| and |v2|.
+ * SameValueZero equates NaNs, equal nonzero values, and zeroes without respect
+ * to their signs.
+ */
+static inline bool
+SameValueZero(double v1, double v2)
+{
+    return mozilla::EqualOrBothNaN(v1, v2);
+}
+
+}  // namespace JS
+
+#endif /* js_Equality_h */