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diff --git a/Source/WTF/wtf/WeakRandom.h b/Source/WTF/wtf/WeakRandom.h
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+/*
+ * Copyright (C) 2009, 2015 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
+ *
+ * Vigna, Sebastiano (2014). "Further scramblings of Marsaglia's xorshift
+ * generators". arXiv:1404.0390 (http://arxiv.org/abs/1404.0390)
+ *
+ * See also https://en.wikipedia.org/wiki/Xorshift.
+ */
+
+#ifndef WeakRandom_h
+#define WeakRandom_h
+
+#include <limits.h>
+#include <wtf/CryptographicallyRandomNumber.h>
+#include <wtf/StdLibExtras.h>
+
+namespace WTF {
+
+// The code used to generate random numbers are inlined manually in JIT code.
+// So it needs to stay in sync with the JIT one.
+class WeakRandom {
+public:
+    WeakRandom(unsigned seed = cryptographicallyRandomNumber())
+    {
+        setSeed(seed);
+    }
+
+    void setSeed(unsigned seed)
+    {
+        m_seed = seed;
+
+        // A zero seed would cause an infinite series of zeroes.
+        if (!seed)
+            seed = 1;
+
+        m_low = seed;
+        m_high = seed;
+        advance();
+    }
+
+    unsigned seed() const { return m_seed; }
+
+    double get()
+    {
+        uint64_t value = advance() & ((1ULL << 53) - 1);
+        return value * (1.0 / (1ULL << 53));
+    }
+
+    unsigned getUint32()
+    {
+        return static_cast<unsigned>(advance());
+    }
+
+    unsigned getUint32(unsigned limit)
+    {
+        if (limit <= 1)
+            return 0;
+        uint64_t cutoff = (static_cast<uint64_t>(std::numeric_limits<unsigned>::max()) + 1) / limit * limit;
+        for (;;) {
+            uint64_t value = getUint32();
+            if (value >= cutoff)
+                continue;
+            return value % limit;
+        }
+    }
+
+    static unsigned lowOffset() { return OBJECT_OFFSETOF(WeakRandom, m_low); }
+    static unsigned highOffset() { return OBJECT_OFFSETOF(WeakRandom, m_high); }
+
+private:
+    uint64_t advance()
+    {
+        uint64_t x = m_low;
+        uint64_t y = m_high;
+        m_low = y;
+        x ^= x << 23;
+        x ^= x >> 17;
+        x ^= y ^ (y >> 26);
+        m_high = x;
+        return x + y;
+    }
+
+    unsigned m_seed;
+    uint64_t m_low;
+    uint64_t m_high;
+};
+
+} // namespace WTF
+
+using WTF::WeakRandom;
+
+#endif // WeakRandom_h