Add xoroshiro128++ PRNG

Xoroshiro128++ is a fast non-cryptographic random generator.
Reference implementation is available at https://prng.di.unimi.it/

Co-Authored-By: Pieter Wuille <pieter@wuille.net>

src/test/util/xoroshiro128plusplus.h

@@ -0,0 +1,71 @@
+// Copyright (c) 2022 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_TEST_UTIL_XOROSHIRO128PLUSPLUS_H
+#define BITCOIN_TEST_UTIL_XOROSHIRO128PLUSPLUS_H
+
+#include <cstdint>
+#include <limits>
+
+/** xoroshiro128++ PRNG. Extremely fast, not appropriate for cryptographic purposes.
+ *
+ * Memory footprint is 128bit, period is 2^128 - 1.
+ * This class is not thread-safe.
+ *
+ * Reference implementation available at https://prng.di.unimi.it/xoroshiro128plusplus.c
+ * See https://prng.di.unimi.it/
+ */
+class XoRoShiRo128PlusPlus
+{
+    uint64_t m_s0;
+    uint64_t m_s1;
+
+    [[nodiscard]] constexpr static uint64_t rotl(uint64_t x, int n)
+    {
+        return (x << n) | (x >> (64 - n));
+    }
+
+    [[nodiscard]] constexpr static uint64_t SplitMix64(uint64_t& seedval) noexcept
+    {
+        uint64_t z = (seedval += UINT64_C(0x9e3779b97f4a7c15));
+        z = (z ^ (z >> 30U)) * UINT64_C(0xbf58476d1ce4e5b9);
+        z = (z ^ (z >> 27U)) * UINT64_C(0x94d049bb133111eb);
+        return z ^ (z >> 31U);
+    }
+
+public:
+    using result_type = uint64_t;
+
+    constexpr explicit XoRoShiRo128PlusPlus(uint64_t seedval) noexcept
+        : m_s0(SplitMix64(seedval)), m_s1(SplitMix64(seedval))
+    {
+    }
+
+    // no copy - that is dangerous, we don't want accidentally copy the RNG and then have two streams
+    // with exactly the same results. If you need a copy, call copy().
+    XoRoShiRo128PlusPlus(const XoRoShiRo128PlusPlus&) = delete;
+    XoRoShiRo128PlusPlus& operator=(const XoRoShiRo128PlusPlus&) = delete;
+
+    // allow moves
+    XoRoShiRo128PlusPlus(XoRoShiRo128PlusPlus&&) = default;
+    XoRoShiRo128PlusPlus& operator=(XoRoShiRo128PlusPlus&&) = default;
+
+    ~XoRoShiRo128PlusPlus() = default;
+
+    constexpr result_type operator()() noexcept
+    {
+        uint64_t s0 = m_s0, s1 = m_s1;
+        const uint64_t result = rotl(s0 + s1, 17) + s0;
+        s1 ^= s0;
+        m_s0 = rotl(s0, 49) ^ s1 ^ (s1 << 21);
+        m_s1 = rotl(s1, 28);
+        return result;
+    }
+
+    static constexpr result_type min() noexcept { return std::numeric_limits<result_type>::min(); }
+    static constexpr result_type max() noexcept { return std::numeric_limits<result_type>::max(); }
+    static constexpr double entropy() noexcept { return 0.0; }
+};
+
+#endif // BITCOIN_TEST_UTIL_XOROSHIRO128PLUSPLUS_H