97 lines
3.0 KiB
C++
97 lines
3.0 KiB
C++
//===--- Random.h - Utilities for random sampling -------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// Utilities for random sampling.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_FUZZMUTATE_RANDOM_H
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#define LLVM_FUZZMUTATE_RANDOM_H
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#include <random>
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#include "llvm/Support/raw_ostream.h"
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namespace llvm {
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/// Return a uniformly distributed random value between \c Min and \c Max
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template <typename T, typename GenT> T uniform(GenT &Gen, T Min, T Max) {
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return std::uniform_int_distribution<T>(Min, Max)(Gen);
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}
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/// Return a uniformly distributed random value of type \c T
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template <typename T, typename GenT> T uniform(GenT &Gen) {
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return uniform<T>(Gen, std::numeric_limits<T>::min(),
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std::numeric_limits<T>::max());
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}
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/// Randomly selects an item by sampling into a set with an unknown number of
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/// elements, which may each be weighted to be more likely choices.
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template <typename T, typename GenT> class ReservoirSampler {
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GenT &RandGen;
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std::remove_const_t<T> Selection = {};
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uint64_t TotalWeight = 0;
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public:
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ReservoirSampler(GenT &RandGen) : RandGen(RandGen) {}
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uint64_t totalWeight() const { return TotalWeight; }
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bool isEmpty() const { return TotalWeight == 0; }
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const T &getSelection() const {
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assert(!isEmpty() && "Nothing selected");
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return Selection;
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}
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explicit operator bool() const { return !isEmpty();}
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const T &operator*() const { return getSelection(); }
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/// Sample each item in \c Items with unit weight
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template <typename RangeT> ReservoirSampler &sample(RangeT &&Items) {
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for (auto &I : Items)
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sample(I, 1);
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return *this;
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}
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/// Sample a single item with the given weight.
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ReservoirSampler &sample(const T &Item, uint64_t Weight) {
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if (!Weight)
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// If the weight is zero, do nothing.
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return *this;
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TotalWeight += Weight;
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// Consider switching from the current element to this one.
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if (uniform<uint64_t>(RandGen, 1, TotalWeight) <= Weight)
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Selection = Item;
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return *this;
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}
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};
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template <typename GenT, typename RangeT,
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typename ElT = std::remove_reference_t<
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decltype(*std::begin(std::declval<RangeT>()))>>
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ReservoirSampler<ElT, GenT> makeSampler(GenT &RandGen, RangeT &&Items) {
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ReservoirSampler<ElT, GenT> RS(RandGen);
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RS.sample(Items);
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return RS;
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}
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template <typename GenT, typename T>
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ReservoirSampler<T, GenT> makeSampler(GenT &RandGen, const T &Item,
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uint64_t Weight) {
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ReservoirSampler<T, GenT> RS(RandGen);
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RS.sample(Item, Weight);
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return RS;
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}
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template <typename T, typename GenT>
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ReservoirSampler<T, GenT> makeSampler(GenT &RandGen) {
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return ReservoirSampler<T, GenT>(RandGen);
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}
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} // End llvm namespace
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#endif // LLVM_FUZZMUTATE_RANDOM_H
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