chromium/third_party/abseil-cpp/absl/random/zipf_distribution.h

// 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.

#ifndef ABSL_RANDOM_ZIPF_DISTRIBUTION_H_
#define ABSL_RANDOM_ZIPF_DISTRIBUTION_H_

#include <cassert>
#include <cmath>
#include <istream>
#include <limits>
#include <ostream>
#include <type_traits>

#include "absl/random/internal/iostream_state_saver.h"
#include "absl/random/internal/traits.h"
#include "absl/random/uniform_real_distribution.h"

namespace absl {
ABSL_NAMESPACE_BEGIN

// absl::zipf_distribution produces random integer-values in the range [0, k],
// distributed according to the unnormalized discrete probability function:
//
//  P(x) = (v + x) ^ -q
//
// The parameter `v` must be greater than 0 and the parameter `q` must be
// greater than 1. If either of these parameters take invalid values then the
// behavior is undefined.
//
// IntType is the result_type generated by the generator. It must be of integral
// type; a static_assert ensures this is the case.
//
// The implementation is based on W.Hormann, G.Derflinger:
//
// "Rejection-Inversion to Generate Variates from Monotone Discrete
// Distributions"
//
// http://eeyore.wu-wien.ac.at/papers/96-04-04.wh-der.ps.gz
//
template <typename IntType = int>
class zipf_distribution { … };

// --------------------------------------------------------------------------
// Implementation details follow
// --------------------------------------------------------------------------

template <typename IntType>
zipf_distribution<IntType>::param_type::param_type(
    typename zipf_distribution<IntType>::result_type k, double q, double v)
    : … { … }

template <typename IntType>
double zipf_distribution<IntType>::param_type::h(double x) const { … }

template <typename IntType>
double zipf_distribution<IntType>::param_type::hinv(double x) const { … }

template <typename IntType>
double zipf_distribution<IntType>::param_type::compute_s() const { … }

template <typename IntType>
double zipf_distribution<IntType>::param_type::pow_negative_q(double x) const { … }

template <typename IntType>
template <typename URBG>
typename zipf_distribution<IntType>::result_type
zipf_distribution<IntType>::operator()(
    URBG& g, const param_type& p) { … }

template <typename CharT, typename Traits, typename IntType>
std::basic_ostream<CharT, Traits>& operator<<(
    std::basic_ostream<CharT, Traits>& os,  // NOLINT(runtime/references)
    const zipf_distribution<IntType>& x) { … }

template <typename CharT, typename Traits, typename IntType>
std::basic_istream<CharT, Traits>& operator>>(
    std::basic_istream<CharT, Traits>& is,  // NOLINT(runtime/references)
    zipf_distribution<IntType>& x) { … }

ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_RANDOM_ZIPF_DISTRIBUTION_H_