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116 lines
2.9 KiB
C++
116 lines
2.9 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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#include <math.h>
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#include "mozilla/Assertions.h"
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#include "mozilla/PodOperations.h"
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#include "mozilla/XorShift128PlusRNG.h"
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using mozilla::non_crypto::XorShift128PlusRNG;
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static void
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TestDumbSequence()
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{
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XorShift128PlusRNG rng(1, 4);
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// Calculated by hand following the algorithm given in the paper. The upper
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// bits are mostly zero because we started with a poor seed; once it has run
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// for a while, we'll get an even mix of ones and zeros in all 64 bits.
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MOZ_RELEASE_ASSERT(rng.next() == 0x800049);
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MOZ_RELEASE_ASSERT(rng.next() == 0x3000186);
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MOZ_RELEASE_ASSERT(rng.next() == 0x400003001145);
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// Using ldexp here lets us write out the mantissa in hex, so we can compare
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// them with the results generated by hand.
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MOZ_RELEASE_ASSERT(rng.nextDouble()
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== ldexp(static_cast<double>(0x1400003105049), -53));
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MOZ_RELEASE_ASSERT(rng.nextDouble()
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== ldexp(static_cast<double>(0x2000802e49146), -53));
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MOZ_RELEASE_ASSERT(rng.nextDouble()
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== ldexp(static_cast<double>(0x248300468544d), -53));
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}
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static size_t
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Population(uint64_t n)
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{
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size_t pop = 0;
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while (n > 0) {
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n &= n-1; // Clear the rightmost 1-bit in n.
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pop++;
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}
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return pop;
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}
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static void
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TestPopulation()
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{
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XorShift128PlusRNG rng(698079309544035222ULL, 6012389156611637584ULL);
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// Give it some time to warm up; it should tend towards more
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// even distributions of zeros and ones.
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for (size_t i = 0; i < 40; i++)
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rng.next();
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for (size_t i = 0; i < 40; i++) {
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size_t pop = Population(rng.next());
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MOZ_RELEASE_ASSERT(24 <= pop && pop <= 40);
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}
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}
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static void
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TestSetState()
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{
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static const uint64_t seed[2] = { 1795644156779822404ULL, 14162896116325912595ULL };
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XorShift128PlusRNG rng(seed[0], seed[1]);
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const size_t n = 10;
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uint64_t log[n];
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for (size_t i = 0; i < n; i++)
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log[i] = rng.next();
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rng.setState(seed[0], seed[1]);
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for (size_t i = 0; i < n; i++)
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MOZ_RELEASE_ASSERT(log[i] == rng.next());
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}
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static void
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TestDoubleDistribution()
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{
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XorShift128PlusRNG rng(0xa207aaede6859736, 0xaca6ca5060804791);
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const size_t n = 100;
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size_t bins[n];
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mozilla::PodArrayZero(bins);
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// This entire file runs in 0.006s on my laptop. Generating
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// more numbers lets us put tighter bounds on the bins.
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for (size_t i = 0; i < 100000; i++) {
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double d = rng.nextDouble();
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MOZ_RELEASE_ASSERT(0.0 <= d && d < 1.0);
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bins[(int) (d * n)]++;
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}
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for (size_t i = 0; i < n; i++) {
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MOZ_RELEASE_ASSERT(900 <= bins[i] && bins[i] <= 1100);
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}
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}
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int
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main()
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{
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TestDumbSequence();
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TestPopulation();
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TestSetState();
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TestDoubleDistribution();
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return 0;
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}
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