Implement std::negative_binomial_distribution

libcudacxx/include/cuda/std/__random/negative_binomial_distribution.h

@@ -0,0 +1,212 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+// SPDX-FileCopyrightText: Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES.
+//
+//===----------------------------------------------------------------------====//
+
+#ifndef _CUDA_STD___NEGATIVE_BINOMIAL_DISTRIBUTION_H
+#define _CUDA_STD___NEGATIVE_BINOMIAL_DISTRIBUTION_H
+
+#include <cuda/std/detail/__config>
+
+#if defined(_CCCL_IMPLICIT_SYSTEM_HEADER_GCC)
+#  pragma GCC system_header
+#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_CLANG)
+#  pragma clang system_header
+#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_MSVC)
+#  pragma system_header
+#endif // no system header
+
+#include <cuda/std/__random/bernoulli_distribution.h>
+#include <cuda/std/__random/gamma_distribution.h>
+#include <cuda/std/__random/is_valid.h>
+#include <cuda/std/__random/poisson_distribution.h>
+#include <cuda/std/limits>
+#if !_CCCL_COMPILER(NVRTC)
+#  include <ios>
+#endif // !_CCCL_COMPILER(NVRTC)
+
+#include <cuda/std/__cccl/prologue.h>
+
+_CCCL_BEGIN_NAMESPACE_CUDA_STD
+
+template <class _IntType = int>
+class negative_binomial_distribution
+{
+  static_assert(__libcpp_random_is_valid_inttype<_IntType>, "IntType must be a supported integer type");
+
+public:
+  // types
+  using result_type = _IntType;
+
+  class param_type
+  {
+    result_type __k_ = result_type{1};
+    double __p_      = 0.5;
+
+  public:
+    using distribution_type = negative_binomial_distribution;
+
+    [[nodiscard]] _CCCL_API constexpr explicit param_type(result_type __k = 1, double __p = 0.5) noexcept
+        : __k_{__k}
+        , __p_{__p}
+    {}
+
+    [[nodiscard]] _CCCL_API constexpr result_type k() const noexcept
+    {
+      return __k_;
+    }
+    [[nodiscard]] _CCCL_API constexpr double p() const noexcept
+    {
+      return __p_;
+    }
+
+    [[nodiscard]] _CCCL_API friend constexpr bool operator==(const param_type& __x, const param_type& __y) noexcept
+    {
+      return __x.__k_ == __y.__k_ && __x.__p_ == __y.__p_;
+    }
+#if _CCCL_STD_VER <= 2017
+    [[nodiscard]] _CCCL_API friend constexpr bool operator!=(const param_type& __x, const param_type& __y) noexcept
+    {
+      return !(__x == __y);
+    }
+#endif // _CCCL_STD_VER <= 2017
+  };
+
+private:
+  param_type __p_{};
+
+public:
+  // constructor and reset functions
+  constexpr negative_binomial_distribution() noexcept = default;
+
+  _CCCL_API constexpr explicit negative_binomial_distribution(result_type __k, double __p = 0.5) noexcept
+      : __p_{__k, __p}
+  {}
+  _CCCL_API constexpr explicit negative_binomial_distribution(const param_type& __p) noexcept
+      : __p_{__p}
+  {}
+  _CCCL_API constexpr void reset() noexcept {}
+
+  // generating functions
+  template <class _URng>
+  [[nodiscard]] _CCCL_API result_type operator()(_URng& __g)
+  {
+    return (*this)(__g, __p_);
+  }
+  template <class _URng>
+  [[nodiscard]] _CCCL_API result_type operator()(_URng& __urng, const param_type& __pr)
+  {
+    static_assert(__cccl_random_is_valid_urng<_URng>, "URng must meet the UniformRandomBitGenerator requirements");
+    result_type __k = __pr.k();
+    double __p      = __pr.p();
+    // When the number of bits in _IntType is small, we are too likely to
+    // overflow __f below to use this technique.
+    if (__k <= 21 * __p && sizeof(_IntType) > 1)
+    {
+      bernoulli_distribution __gen(__p);
+      result_type __f = 0;
+      result_type __s = 0;
+      while (__s < __k)
+      {
+        if (__gen(__urng))
+        {
+          ++__s;
+        }
+        else
+        {
+          ++__f;
+        }
+      }
+      return __f;
+    }
+    return poisson_distribution<result_type>(gamma_distribution<double>(__k, (1 - __p) / __p)(__urng))(__urng);
+  }
+
+  // property functions
+  [[nodiscard]] _CCCL_API constexpr result_type k() const noexcept
+  {
+    return __p_.k();
+  }
+  [[nodiscard]] _CCCL_API constexpr double p() const noexcept
+  {
+    return __p_.p();
+  }
+
+  [[nodiscard]] _CCCL_API constexpr param_type param() const noexcept
+  {
+    return __p_;
+  }
+  _CCCL_API constexpr void param(const param_type& __p) noexcept
+  {
+    __p_ = __p;
+  }
+
+  [[nodiscard]] _CCCL_API static constexpr result_type min() noexcept
+  {
+    return 0;
+  }
+  [[nodiscard]] _CCCL_API static constexpr result_type max() noexcept
+  {
+    return numeric_limits<result_type>::max();
+  }
+
+  [[nodiscard]] _CCCL_API friend constexpr bool
+  operator==(const negative_binomial_distribution& __x, const negative_binomial_distribution& __y) noexcept
+  {
+    return __x.__p_ == __y.__p_;
+  }
+#if _CCCL_STD_VER <= 2017
+  [[nodiscard]] _CCCL_API friend constexpr bool
+  operator!=(const negative_binomial_distribution& __x, const negative_binomial_distribution& __y) noexcept
+  {
+    return !(__x == __y);
+  }
+#endif // _CCCL_STD_VER <= 2017
+
+#if !_CCCL_COMPILER(NVRTC)
+  template <class _CharT, class _Traits>
+  friend ::std::basic_ostream<_CharT, _Traits>&
+  operator<<(::std::basic_ostream<_CharT, _Traits>& __os, const negative_binomial_distribution& __x)
+  {
+    using _Ostream = ::std::basic_ostream<_CharT, _Traits>;
+    auto __flags   = __os.flags();
+    __os.flags(_Ostream::dec | _Ostream::left | _Ostream::scientific);
+    _CharT __sp      = __os.widen(' ');
+    _CharT __fill    = __os.fill(__sp);
+    auto __precision = __os.precision(numeric_limits<double>::max_digits10);
+    __os << __x.k() << __sp << __x.p();
+    __os.precision(__precision);
+    __os.fill(__fill);
+    __os.flags(__flags);
+    return __os;
+  }
+
+  template <class _CharT, class _Traits>
+  friend ::std::basic_istream<_CharT, _Traits>&
+  operator>>(::std::basic_istream<_CharT, _Traits>& __is, negative_binomial_distribution& __x)
+  {
+    using _Istream = ::std::basic_istream<_CharT, _Traits>;
+    auto __flags   = __is.flags();
+    __is.flags(_Istream::skipws);
+    result_type __k;
+    double __p;
+    __is >> __k >> __p;
+    if (!__is.fail())
+    {
+      __x.param(param_type(__k, __p));
+    }
+    __is.flags(__flags);
+    return __is;
+  }
+#endif // !_CCCL_COMPILER(NVRTC)
+};
+
+_CCCL_END_NAMESPACE_CUDA_STD
+
+#include <cuda/std/__cccl/epilogue.h>
+
+#endif // _CUDA_STD___NEGATIVE_BINOMIAL_DISTRIBUTION_H

libcudacxx/include/cuda/std/__random_

@@ -27,6 +27,7 @@
 #include <cuda/std/__random/gamma_distribution.h>
 #include <cuda/std/__random/linear_congruential_engine.h>
 #include <cuda/std/__random/lognormal_distribution.h>
+#include <cuda/std/__random/negative_binomial_distribution.h>
 #include <cuda/std/__random/normal_distribution.h>
 #include <cuda/std/__random/philox_engine.h>
 #include <cuda/std/__random/poisson_distribution.h>

libcudacxx/test/libcudacxx/std/random/distribution/negative_binomial.pass.cpp

@@ -0,0 +1,60 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+// SPDX-FileCopyrightText: Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES.
+//
+//===----------------------------------------------------------------------===//
+//
+// REQUIRES: long_tests
+
+// <random>
+
+// template<class IntType = int>
+// class negative_binomial_distribution
+
+#include <cuda/std/__random_>
+#include <cuda/std/cassert>
+
+#include "random_utilities/stats_functions.h"
+#include "random_utilities/test_distribution.h"
+#include "test_macros.h"
+
+template <class T>
+struct negative_binomial_cdf
+{
+  using P = typename cuda::std::negative_binomial_distribution<T>::param_type;
+
+  __host__ __device__ double operator()(double x, const P& p) const
+  {
+    // CDF: F(x; k, p) = I_p(k, x+1) where I_p is the regularized incomplete beta function
+    // This represents P(X <= x) where X is the number of failures before k successes
+    if (x < 0)
+    {
+      return 0.0;
+    }
+    double k    = static_cast<double>(p.k());
+    double prob = p.p();
+    return incomplete_beta(k, cuda::std::floor(x) + 1.0, prob);
+  }
+};
+
+template <class T>
+__host__ __device__ void test()
+{
+  // Cannot be constexpr due to gamma_distribution and log/exp
+  [[maybe_unused]] const bool test_constexpr = false;
+  using D                                    = cuda::std::negative_binomial_distribution<T>;
+  using P                                    = typename D::param_type;
+  using G                                    = cuda::std::philox4x64;
+  cuda::std::array<P, 5> params              = {P(5, 0.5), P(10, 0.3), P(3, 0.7), P(15, 0.4), P(20, 0.6)};
+  test_distribution<D, false, G, test_constexpr>(params, negative_binomial_cdf<T>{});
+}
+
+int main(int, char**)
+{
+  test<int>();
+  test<long>();
+  return 0;
+}