/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ /* vim: set ts=8 sts=2 et sw=2 tw=80: */ /* 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/. */
/* The xorshift128+ pseudo-random number generator. */
/* * A stream of pseudo-random numbers generated using the xorshift+ technique * described here: * * Vigna, Sebastiano (2014). "Further scramblings of Marsaglia's xorshift * generators". arXiv:1404.0390 (http://arxiv.org/abs/1404.0390) * * That paper says: * * In particular, we propose a tightly coded xorshift128+ generator that * does not fail systematically any test from the BigCrush suite of TestU01 * (even reversed) and generates 64 pseudorandom bits in 1.10 ns on an * Intel(R) Core(TM) i7-4770 CPU @3.40GHz (Haswell). It is the fastest * generator we are aware of with such empirical statistical properties. * * The stream of numbers produced by this method repeats every 2**128 - 1 calls * (i.e. never, for all practical purposes). Zero appears 2**64 - 1 times in * this period; all other numbers appear 2**64 times. Additionally, each *bit* * in the produced numbers repeats every 2**128 - 1 calls. * * This generator is not suitable as a cryptographically secure random number * generator.
*/ class XorShift128PlusRNG {
uint64_t mState[2];
public: /* * Construct a xorshift128+ pseudo-random number stream using |aInitial0| and * |aInitial1| as the initial state. These MUST NOT both be zero. * * If the initial states contain many zeros, for a few iterations you'll see * many zeroes in the generated numbers. It's suggested to seed a SplitMix64 * generator <http://xorshift.di.unimi.it/splitmix64.c> and use its first two * outputs to seed xorshift128+.
*/
XorShift128PlusRNG(uint64_t aInitial0, uint64_t aInitial1) {
setState(aInitial0, aInitial1);
}
/** * Return a pseudo-random 64-bit number.
*/
MOZ_NO_SANITIZE_UNSIGNED_OVERFLOW
uint64_t next() { /* * The offsetOfState*() methods below are provided so that exceedingly-rare * callers that want to observe or poke at RNG state in C++ type-system- * ignoring means can do so. Don't change the next() or nextDouble() * algorithms without altering code that uses offsetOfState*()!
*/
uint64_t s1 = mState[0]; const uint64_t s0 = mState[1];
mState[0] = s0;
s1 ^= s1 << 23;
mState[1] = s1 ^ s0 ^ (s1 >> 17) ^ (s0 >> 26); return mState[1] + s0;
}
/* * Return a pseudo-random floating-point value in the range [0, 1). More * precisely, choose an integer in the range [0, 2**53) and divide it by * 2**53. Given the 2**128 - 1 period noted above, the produced doubles are * all but uniformly distributed in this range.
*/ double nextDouble() { /* * Because the IEEE 64-bit floating point format stores the leading '1' bit * of the mantissa implicitly, it effectively represents a mantissa in the * range [0, 2**53) in only 52 bits. FloatingPoint<double>::kExponentShift * is the width of the bitfield in the in-memory format, so we must add one * to get the mantissa's range.
*/ static constexpr int kMantissaBits =
mozilla::FloatingPoint<double>::kExponentShift + 1;
uint64_t mantissa = next() & ((UINT64_C(1) << kMantissaBits) - 1); returndouble(mantissa) / (UINT64_C(1) << kMantissaBits);
}
/* * Set the stream's current state to |aState0| and |aState1|. These must not * both be zero; ideally, they should have an almost even mix of zero and one * bits.
*/ void setState(uint64_t aState0, uint64_t aState1) {
MOZ_ASSERT(aState0 || aState1);
mState[0] = aState0;
mState[1] = aState1;
}
Die Informationen auf dieser Webseite wurden
nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit,
noch Qualität der bereit gestellten Informationen zugesichert.
Bemerkung:
Die farbliche Syntaxdarstellung ist noch experimentell.
