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/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Stockfish is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
This file is based on original code by Heinz van Saanen and is
available under the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
*/
#if !defined(RKISS_H_INCLUDED)
#define RKISS_H_INCLUDED
#include "types.h"
/// RKISS is our pseudo random number generator (PRNG) used to compute hash keys.
/// George Marsaglia invented the RNG-Kiss-family in the early 90's. This is a
/// specific version that Heinz van Saanen derived from some public domain code
/// by Bob Jenkins. Following the feature list, as tested by Heinz.
///
/// - Quite platform independent
/// - Passes ALL dieharder tests! Here *nix sys-rand() e.g. fails miserably:-)
/// - ~12 times faster than my *nix sys-rand()
/// - ~4 times faster than SSE2-version of Mersenne twister
/// - Average cycle length: ~2^126
/// - 64 bit seed
/// - Return doubles with a full 53 bit mantissa
/// - Thread safe
class RKISS {
// Keep variables always together
struct S { uint64_t a, b, c, d; } s;
uint64_t rotate(uint64_t x, uint64_t k) const {
return (x << k) | (x >> (64 - k));
}
// Return 64 bit unsigned integer in between [0, 2^64 - 1]
uint64_t rand64() {
const uint64_t
e = s.a - rotate(s.b, 7);
s.a = s.b ^ rotate(s.c, 13);
s.b = s.c + rotate(s.d, 37);
s.c = s.d + e;
return s.d = e + s.a;
}
// Init seed and scramble a few rounds
void raninit() {
s.a = 0xf1ea5eed;
s.b = s.c = s.d = 0xd4e12c77;
for (int i = 0; i < 73; i++)
rand64();
}
public:
RKISS() { raninit(); }
template<typename T> T rand() { return T(rand64()); }
};
#endif // !defined(RKISS_H_INCLUDED)
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