TomZ
34 lines
1.1 KiB
C++
34 lines
1.1 KiB
C++
// Copyright (c) 2019 The Bitcoin developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#ifndef BITCOIN_TEST_LCG_H
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#define BITCOIN_TEST_LCG_H
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#include <cstdint>
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// Simple 32-bit linear congruential generator with 64-bit internal state,
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// often called as "MMIX by Donald Knuth". Knuth attributes the multiplier
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// to C. E. Haynes and the increment is not crucial (it only need be odd).
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// Knuth, Donald (1997). Seminumerical Algorithms Vol2. Sec 3.3.4. 3rd Ed.
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//
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// Low bits have short period, hence we use high bits which should have
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// the same period as the entire generator (2^64).
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class MMIXLinearCongruentialGenerator {
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uint64_t state;
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public:
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MMIXLinearCongruentialGenerator(uint64_t initialstate = 0)
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: state(initialstate) {}
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// pseudorandom, except the first value returned is the seed provided
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// (thus starting with 0, by default)
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uint32_t next() {
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uint32_t ret = state >> 32;
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state = state * 6364136223846793005 + 1442695040888963407;
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return ret;
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}
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};
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#endif // BITCOIN_TEST_LCG_H
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