distributions.h - mozsearch

// Copyright 2017 The Abseil Authors.

//

// Licensed under the Apache License, Version 2.0 (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

//

//      https://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

//

// -----------------------------------------------------------------------------

// File: distributions.h

// -----------------------------------------------------------------------------

//

// This header defines functions representing distributions, which you use in

// combination with an Abseil random bit generator to produce random values

// according to the rules of that distribution.

//

// The Abseil random library defines the following distributions within this

// file:

//

//   * `absl::Uniform` for uniform (constant) distributions having constant

//     probability

//   * `absl::Bernoulli` for discrete distributions having exactly two outcomes

//   * `absl::Beta` for continuous distributions parameterized through two

//     free parameters

//   * `absl::Exponential` for discrete distributions of events occurring

//     continuously and independently at a constant average rate

//   * `absl::Gaussian` (also known as "normal distributions") for continuous

//     distributions using an associated quadratic function

//   * `absl::LogUniform` for continuous uniform distributions where the log

//     to the given base of all values is uniform

//   * `absl::Poisson` for discrete probability distributions that express the

//     probability of a given number of events occurring within a fixed interval

//   * `absl::Zipf` for discrete probability distributions commonly used for

//     modelling of rare events

//

// Prefer use of these distribution function classes over manual construction of

// your own distribution classes, as it allows library maintainers greater

// flexibility to change the underlying implementation in the future.

#ifndef ABSL_RANDOM_DISTRIBUTIONS_H_

#define ABSL_RANDOM_DISTRIBUTIONS_H_

#include <algorithm>

#include <cmath>

#include <limits>

#include <random>

#include <type_traits>

#include "absl/base/internal/inline_variable.h"

#include "absl/random/bernoulli_distribution.h"

#include "absl/random/beta_distribution.h"

#include "absl/random/exponential_distribution.h"

#include "absl/random/gaussian_distribution.h"

#include "absl/random/internal/distribution_caller.h"  // IWYU pragma: export

#include "absl/random/internal/uniform_helper.h"  // IWYU pragma: export

#include "absl/random/log_uniform_int_distribution.h"

#include "absl/random/poisson_distribution.h"

#include "absl/random/uniform_int_distribution.h"

#include "absl/random/uniform_real_distribution.h"

#include "absl/random/zipf_distribution.h"

namespace absl {

ABSL_NAMESPACE_BEGIN

ABSL_INTERNAL_INLINE_CONSTEXPR(IntervalClosedClosedTag, IntervalClosedClosed,

                               {});

ABSL_INTERNAL_INLINE_CONSTEXPR(IntervalClosedClosedTag, IntervalClosed, {});

ABSL_INTERNAL_INLINE_CONSTEXPR(IntervalClosedOpenTag, IntervalClosedOpen, {});

ABSL_INTERNAL_INLINE_CONSTEXPR(IntervalOpenOpenTag, IntervalOpenOpen, {});

ABSL_INTERNAL_INLINE_CONSTEXPR(IntervalOpenOpenTag, IntervalOpen, {});

ABSL_INTERNAL_INLINE_CONSTEXPR(IntervalOpenClosedTag, IntervalOpenClosed, {});

// -----------------------------------------------------------------------------

// absl::Uniform<T>(tag, bitgen, lo, hi)

// -----------------------------------------------------------------------------

//

// `absl::Uniform()` produces random values of type `T` uniformly distributed in

// a defined interval {lo, hi}. The interval `tag` defines the type of interval

// which should be one of the following possible values:

//

//   * `absl::IntervalOpenOpen`

//   * `absl::IntervalOpenClosed`

//   * `absl::IntervalClosedOpen`

//   * `absl::IntervalClosedClosed`

//

// where "open" refers to an exclusive value (excluded) from the output, while

// "closed" refers to an inclusive value (included) from the output.

//

// In the absence of an explicit return type `T`, `absl::Uniform()` will deduce

// the return type based on the provided endpoint arguments {A lo, B hi}.

// Given these endpoints, one of {A, B} will be chosen as the return type, if

// a type can be implicitly converted into the other in a lossless way. The

// lack of any such implicit conversion between {A, B} will produce a

// compile-time error

//

// See https://en.wikipedia.org/wiki/Uniform_distribution_(continuous)

//

// Example:

//

//   absl::BitGen bitgen;

//

//   // Produce a random float value between 0.0 and 1.0, inclusive

//   auto x = absl::Uniform(absl::IntervalClosedClosed, bitgen, 0.0f, 1.0f);

//

//   // The most common interval of `absl::IntervalClosedOpen` is available by

//   // default:

//

//   auto x = absl::Uniform(bitgen, 0.0f, 1.0f);

//

//   // Return-types are typically inferred from the arguments, however callers

//   // can optionally provide an explicit return-type to the template.

//

//   auto x = absl::Uniform<float>(bitgen, 0, 1);

//

template <typename R = void, typename TagType, typename URBG>

typename absl::enable_if_t<!std::is_same<R, void>::value, R>  //

Uniform(TagType tag,

        URBG&& urbg,  // NOLINT(runtime/references)

        R lo, R hi) {

  using gen_t = absl::decay_t<URBG>;

  using distribution_t = random_internal::UniformDistributionWrapper<R>;

  auto a = random_internal::uniform_lower_bound(tag, lo, hi);

  auto b = random_internal::uniform_upper_bound(tag, lo, hi);

  if (!random_internal::is_uniform_range_valid(a, b)) return lo;

  return random_internal::DistributionCaller<gen_t>::template Call<

      distribution_t>(&urbg, tag, lo, hi);

// absl::Uniform<T>(bitgen, lo, hi)

//

// Overload of `Uniform()` using the default closed-open interval of [lo, hi),

// and returning values of type `T`

template <typename R = void, typename URBG>

typename absl::enable_if_t<!std::is_same<R, void>::value, R>  //

Uniform(URBG&& urbg,  // NOLINT(runtime/references)

        R lo, R hi) {

  using gen_t = absl::decay_t<URBG>;

  using distribution_t = random_internal::UniformDistributionWrapper<R>;

  constexpr auto tag = absl::IntervalClosedOpen;

  auto a = random_internal::uniform_lower_bound(tag, lo, hi);

  auto b = random_internal::uniform_upper_bound(tag, lo, hi);

  if (!random_internal::is_uniform_range_valid(a, b)) return lo;

  return random_internal::DistributionCaller<gen_t>::template Call<

      distribution_t>(&urbg, lo, hi);

// absl::Uniform(tag, bitgen, lo, hi)

//

// Overload of `Uniform()` using different (but compatible) lo, hi types. Note

// that a compile-error will result if the return type cannot be deduced

// correctly from the passed types.

template <typename R = void, typename TagType, typename URBG, typename A,

          typename B>

typename absl::enable_if_t<std::is_same<R, void>::value,

                           random_internal::uniform_inferred_return_t<A, B>>

Uniform(TagType tag,

        URBG&& urbg,  // NOLINT(runtime/references)

        A lo, B hi) {

  using gen_t = absl::decay_t<URBG>;

  using return_t = typename random_internal::uniform_inferred_return_t<A, B>;

  using distribution_t = random_internal::UniformDistributionWrapper<return_t>;

  auto a = random_internal::uniform_lower_bound<return_t>(tag, lo, hi);

  auto b = random_internal::uniform_upper_bound<return_t>(tag, lo, hi);

  if (!random_internal::is_uniform_range_valid(a, b)) return lo;

  return random_internal::DistributionCaller<gen_t>::template Call<

      distribution_t>(&urbg, tag, static_cast<return_t>(lo),

                                static_cast<return_t>(hi));

// absl::Uniform(bitgen, lo, hi)

//

// Overload of `Uniform()` using different (but compatible) lo, hi types and the

// default closed-open interval of [lo, hi). Note that a compile-error will

// result if the return type cannot be deduced correctly from the passed types.

template <typename R = void, typename URBG, typename A, typename B>

typename absl::enable_if_t<std::is_same<R, void>::value,

                           random_internal::uniform_inferred_return_t<A, B>>

Uniform(URBG&& urbg,  // NOLINT(runtime/references)

        A lo, B hi) {

  using gen_t = absl::decay_t<URBG>;

  using return_t = typename random_internal::uniform_inferred_return_t<A, B>;

  using distribution_t = random_internal::UniformDistributionWrapper<return_t>;

  constexpr auto tag = absl::IntervalClosedOpen;

  auto a = random_internal::uniform_lower_bound<return_t>(tag, lo, hi);

  auto b = random_internal::uniform_upper_bound<return_t>(tag, lo, hi);

  if (!random_internal::is_uniform_range_valid(a, b)) return lo;

  return random_internal::DistributionCaller<gen_t>::template Call<

      distribution_t>(&urbg, static_cast<return_t>(lo),

                                static_cast<return_t>(hi));

// absl::Uniform<unsigned T>(bitgen)

//

// Overload of Uniform() using the minimum and maximum values of a given type

// `T` (which must be unsigned), returning a value of type `unsigned T`

template <typename R, typename URBG>

typename absl::enable_if_t<!std::is_signed<R>::value, R>  //

Uniform(URBG&& urbg) {  // NOLINT(runtime/references)

  using gen_t = absl::decay_t<URBG>;

  using distribution_t = random_internal::UniformDistributionWrapper<R>;

  return random_internal::DistributionCaller<gen_t>::template Call<

      distribution_t>(&urbg);

// -----------------------------------------------------------------------------

// absl::Bernoulli(bitgen, p)

// -----------------------------------------------------------------------------

//

// `absl::Bernoulli` produces a random boolean value, with probability `p`

// (where 0.0 <= p <= 1.0) equaling `true`.

//

// Prefer `absl::Bernoulli` to produce boolean values over other alternatives

// such as comparing an `absl::Uniform()` value to a specific output.

//

// See https://en.wikipedia.org/wiki/Bernoulli_distribution

//

// Example:

//

//   absl::BitGen bitgen;

//   ...

//   if (absl::Bernoulli(bitgen, 1.0/3721.0)) {

//     std::cout << "Asteroid field navigation successful.";

//   }

//

template <typename URBG>

bool Bernoulli(URBG&& urbg,  // NOLINT(runtime/references)

               double p) {

  using gen_t = absl::decay_t<URBG>;

  using distribution_t = absl::bernoulli_distribution;

  return random_internal::DistributionCaller<gen_t>::template Call<

      distribution_t>(&urbg, p);

// -----------------------------------------------------------------------------

// absl::Beta<T>(bitgen, alpha, beta)

// -----------------------------------------------------------------------------

//

// `absl::Beta` produces a floating point number distributed in the closed

// interval [0,1] and parameterized by two values `alpha` and `beta` as per a

// Beta distribution. `T` must be a floating point type, but may be inferred

// from the types of `alpha` and `beta`.

//

// See https://en.wikipedia.org/wiki/Beta_distribution.

//

// Example:

//

//   absl::BitGen bitgen;

//   ...

//   double sample = absl::Beta(bitgen, 3.0, 2.0);

//

template <typename RealType, typename URBG>

RealType Beta(URBG&& urbg,  // NOLINT(runtime/references)

              RealType alpha, RealType beta) {

  static_assert(

      std::is_floating_point<RealType>::value,

      "Template-argument 'RealType' must be a floating-point type, in "

      "absl::Beta<RealType, URBG>(...)");

  using gen_t = absl::decay_t<URBG>;

  using distribution_t = typename absl::beta_distribution<RealType>;

  return random_internal::DistributionCaller<gen_t>::template Call<

      distribution_t>(&urbg, alpha, beta);

// -----------------------------------------------------------------------------

// absl::Exponential<T>(bitgen, lambda = 1)

// -----------------------------------------------------------------------------

//

// `absl::Exponential` produces a floating point number representing the

// distance (time) between two consecutive events in a point process of events

// occurring continuously and independently at a constant average rate. `T` must

// be a floating point type, but may be inferred from the type of `lambda`.

//

// See https://en.wikipedia.org/wiki/Exponential_distribution.

//

// Example:

//

//   absl::BitGen bitgen;

//   ...

//   double call_length = absl::Exponential(bitgen, 7.0);

//

template <typename RealType, typename URBG>

RealType Exponential(URBG&& urbg,  // NOLINT(runtime/references)

                     RealType lambda = 1) {

  static_assert(

      std::is_floating_point<RealType>::value,

      "Template-argument 'RealType' must be a floating-point type, in "

      "absl::Exponential<RealType, URBG>(...)");

  using gen_t = absl::decay_t<URBG>;

  using distribution_t = typename absl::exponential_distribution<RealType>;

  return random_internal::DistributionCaller<gen_t>::template Call<

      distribution_t>(&urbg, lambda);

// -----------------------------------------------------------------------------

// absl::Gaussian<T>(bitgen, mean = 0, stddev = 1)

// -----------------------------------------------------------------------------

//

// `absl::Gaussian` produces a floating point number selected from the Gaussian

// (ie. "Normal") distribution. `T` must be a floating point type, but may be

// inferred from the types of `mean` and `stddev`.

//

// See https://en.wikipedia.org/wiki/Normal_distribution

//

// Example:

//

//   absl::BitGen bitgen;

//   ...

//   double giraffe_height = absl::Gaussian(bitgen, 16.3, 3.3);

//

template <typename RealType, typename URBG>

RealType Gaussian(URBG&& urbg,  // NOLINT(runtime/references)

                  RealType mean = 0, RealType stddev = 1) {

  static_assert(

      std::is_floating_point<RealType>::value,

      "Template-argument 'RealType' must be a floating-point type, in "

      "absl::Gaussian<RealType, URBG>(...)");

  using gen_t = absl::decay_t<URBG>;

  using distribution_t = typename absl::gaussian_distribution<RealType>;

  return random_internal::DistributionCaller<gen_t>::template Call<

      distribution_t>(&urbg, mean, stddev);

// -----------------------------------------------------------------------------

// absl::LogUniform<T>(bitgen, lo, hi, base = 2)

// -----------------------------------------------------------------------------

//

// `absl::LogUniform` produces random values distributed where the log to a

// given base of all values is uniform in a closed interval [lo, hi]. `T` must

// be an integral type, but may be inferred from the types of `lo` and `hi`.

//

// I.e., `LogUniform(0, n, b)` is uniformly distributed across buckets

// [0], [1, b-1], [b, b^2-1] .. [b^(k-1), (b^k)-1] .. [b^floor(log(n, b)), n]

// and is uniformly distributed within each bucket.

//

// The resulting probability density is inversely related to bucket size, though

// values in the final bucket may be more likely than previous values. (In the

// extreme case where n = b^i the final value will be tied with zero as the most

// probable result.

//

// If `lo` is nonzero then this distribution is shifted to the desired interval,

// so LogUniform(lo, hi, b) is equivalent to LogUniform(0, hi-lo, b)+lo.

//

// See http://ecolego.facilia.se/ecolego/show/Log-Uniform%20Distribution

//

// Example:

//

//   absl::BitGen bitgen;

//   ...

//   int v = absl::LogUniform(bitgen, 0, 1000);

//

template <typename IntType, typename URBG>

IntType LogUniform(URBG&& urbg,  // NOLINT(runtime/references)

                   IntType lo, IntType hi, IntType base = 2) {

  static_assert(random_internal::IsIntegral<IntType>::value,

                "Template-argument 'IntType' must be an integral type, in "

                "absl::LogUniform<IntType, URBG>(...)");

  using gen_t = absl::decay_t<URBG>;

  using distribution_t = typename absl::log_uniform_int_distribution<IntType>;

  return random_internal::DistributionCaller<gen_t>::template Call<

      distribution_t>(&urbg, lo, hi, base);

// -----------------------------------------------------------------------------

// absl::Poisson<T>(bitgen, mean = 1)

// -----------------------------------------------------------------------------

//

// `absl::Poisson` produces discrete probabilities for a given number of events

// occurring within a fixed interval within the closed interval [0, max]. `T`

// must be an integral type.

//

// See https://en.wikipedia.org/wiki/Poisson_distribution

//

// Example:

//

//   absl::BitGen bitgen;

//   ...

//   int requests_per_minute = absl::Poisson<int>(bitgen, 3.2);

//

template <typename IntType, typename URBG>

IntType Poisson(URBG&& urbg,  // NOLINT(runtime/references)

                double mean = 1.0) {

  static_assert(random_internal::IsIntegral<IntType>::value,

                "Template-argument 'IntType' must be an integral type, in "

                "absl::Poisson<IntType, URBG>(...)");

  using gen_t = absl::decay_t<URBG>;

  using distribution_t = typename absl::poisson_distribution<IntType>;

  return random_internal::DistributionCaller<gen_t>::template Call<

      distribution_t>(&urbg, mean);

// -----------------------------------------------------------------------------

// absl::Zipf<T>(bitgen, hi = max, q = 2, v = 1)

// -----------------------------------------------------------------------------

//

// `absl::Zipf` produces discrete probabilities commonly used for modelling of

// rare events over the closed interval [0, hi]. The parameters `v` and `q`

// determine the skew of the distribution. `T`  must be an integral type, but

// may be inferred from the type of `hi`.

//

// See http://mathworld.wolfram.com/ZipfDistribution.html

//

// Example:

//

//   absl::BitGen bitgen;

//   ...

//   int term_rank = absl::Zipf<int>(bitgen);

//

template <typename IntType, typename URBG>

IntType Zipf(URBG&& urbg,  // NOLINT(runtime/references)

             IntType hi = (std::numeric_limits<IntType>::max)(), double q = 2.0,

             double v = 1.0) {

  static_assert(random_internal::IsIntegral<IntType>::value,

                "Template-argument 'IntType' must be an integral type, in "

                "absl::Zipf<IntType, URBG>(...)");

  using gen_t = absl::decay_t<URBG>;

  using distribution_t = typename absl::zipf_distribution<IntType>;

  return random_internal::DistributionCaller<gen_t>::template Call<

      distribution_t>(&urbg, hi, q, v);

ABSL_NAMESPACE_END

}  // namespace absl

#endif  // ABSL_RANDOM_DISTRIBUTIONS_H_

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