diff -r 000000000000 -r 6474c204b198 js/src/jslibmath.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jslibmath.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,76 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * 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/. */
+
+#ifndef jslibmath_h
+#define jslibmath_h
+
+#include "mozilla/FloatingPoint.h"
+
+#include <math.h>
+
+#include "jsnum.h"
+
+/*
+ * Use system provided math routines.
+ */
+
+/* The right copysign function is not always named the same thing. */
+#ifdef __GNUC__
+#define js_copysign __builtin_copysign
+#elif defined _WIN32
+#define js_copysign _copysign
+#else
+#define js_copysign copysign
+#endif
+
+/* Consistency wrapper for platform deviations in fmod() */
+static inline double
+js_fmod(double d, double d2)
+{
+#ifdef XP_WIN
+    /*
+     * Workaround MS fmod bug where 42 % (1/0) => NaN, not 42.
+     * Workaround MS fmod bug where -0 % -N => 0, not -0.
+     */
+    if ((mozilla::IsFinite(d) && mozilla::IsInfinite(d2)) ||
+        (d == 0 && mozilla::IsFinite(d2))) {
+        return d;
+    }
+#endif
+    return fmod(d, d2);
+}
+
+namespace js {
+
+inline double
+NumberDiv(double a, double b)
+{
+    if (b == 0) {
+        if (a == 0 || mozilla::IsNaN(a)
+#ifdef XP_WIN
+            || mozilla::IsNaN(b) /* XXX MSVC miscompiles such that (NaN == 0) */
+#endif
+        )
+            return JS::GenericNaN();
+
+        if (mozilla::IsNegative(a) != mozilla::IsNegative(b))
+            return mozilla::NegativeInfinity<double>();
+        return mozilla::PositiveInfinity<double>();
+    }
+
+    return a / b;
+}
+
+inline double
+NumberMod(double a, double b) {
+    if (b == 0)
+        return JS::GenericNaN();
+    return js_fmod(a, b);
+}
+
+}
+
+#endif /* jslibmath_h */