[PATCH v2] libstdc++: libstdc++: Update underlying gamma_distribution in param() [PR123409]
Jonathan Wakely
jwakely@redhat.com
Wed Sep 16 16:40:19 GMT 2026
On Wed, 16 Sept 2026 at 10:44, Tomasz Kamiński <tkaminsk@redhat.com> wrote:
>
> This updates the underlying gamma distribution in the param function by
> invoking the param function on the corresponding member:
> * _M_gd for negative_binomial_distribution, student_t_distribution;
> * _M_gd_x, _M_gd_y for fisher_f_distribution.
>
> The distribution_param.cc test, validates that for all distributions,
> constructing or setting params results in equal distribution that
> produces same values. The test uses -ffloat-store for -m32, following
> chi_squared_distribution test for PR83833 - that is removed, as all
> cases are covered in new test.
>
> libstdc++-v3/ChangeLog:
>
> PR libstdc++/123409
> * include/bits/random.h (negative_binomial_distribution::param)
> (fisher_f_distribution::param, student_t_distribution::param):
> Updated underlying gamma distributions, by calling param.
> (chi_squared_distribution::param): Use type alias and parenthesis
> for consistency.
> * testsuite/26_numerics/random/distribution_param.cc: New test.
> * testsuite/26_numerics/random/chi_squared_distribution/83833.cc: Removed,
> covered by above.
> ---
> v2 was written from scratch, as I started with the test for all distributions,
> and fixed ones for which they are failing (and I about the patch existing).
> Still sending is as v2, so we know that patch was handled.
>
> Tested on x86_64-linux. *random* test passed in all standard modes,
> -m32, debug and assertions. OK for trunk, and backports up to 14?
OK for all
>
>
> libstdc++-v3/include/bits/random.h | 32 ++++++++--
> .../random/chi_squared_distribution/83833.cc | 41 -------------
> .../26_numerics/random/distribution_param.cc | 60 +++++++++++++++++++
> 3 files changed, 86 insertions(+), 47 deletions(-)
> delete mode 100644 libstdc++-v3/testsuite/26_numerics/random/chi_squared_distribution/83833.cc
> create mode 100644 libstdc++-v3/testsuite/26_numerics/random/distribution_param.cc
>
> diff --git a/libstdc++-v3/include/bits/random.h b/libstdc++-v3/include/bits/random.h
> index cfec087f0cd..1a2900e2b9d 100644
> --- a/libstdc++-v3/include/bits/random.h
> +++ b/libstdc++-v3/include/bits/random.h
> @@ -3559,9 +3559,10 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> param(const param_type& __param)
> {
> _M_param = __param;
> - typedef typename std::gamma_distribution<result_type>::param_type
> - param_type;
> - _M_gd.param(param_type{__param.n() / 2});
> +
> + using param_type
> + = typename std::gamma_distribution<result_type>::param_type;
> + _M_gd.param(param_type(__param.n() / 2));
> }
>
> /**
> @@ -4015,7 +4016,14 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> */
> void
> param(const param_type& __param)
> - { _M_param = __param; }
> + {
> + _M_param = __param;
> +
> + using param_type
> + = typename std::gamma_distribution<result_type>::param_type;
> + _M_gd_x.param(param_type(__param.m() / 2));
> + _M_gd_y.param(param_type(__param.n() / 2));
> + }
>
> /**
> * @brief Returns the greatest lower bound value of the distribution.
> @@ -4244,7 +4252,13 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> */
> void
> param(const param_type& __param)
> - { _M_param = __param; }
> + {
> + _M_param = __param;
> +
> + using param_type
> + = typename std::gamma_distribution<result_type>::param_type;
> + _M_gd.param(param_type(__param.n() / 2, 2));
> + }
>
> /**
> * @brief Returns the greatest lower bound value of the distribution.
> @@ -5175,7 +5189,13 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> */
> void
> param(const param_type& __param)
> - { _M_param = __param; }
> + {
> + _M_param = __param;
> +
> + using param_type
> + = typename std::gamma_distribution<double>::param_type;
> + _M_gd.param(param_type(__param.k(), (1.0 - __param.p()) / __param.p()));
> + }
>
> /**
> * @brief Returns the greatest lower bound value of the distribution.
> diff --git a/libstdc++-v3/testsuite/26_numerics/random/chi_squared_distribution/83833.cc b/libstdc++-v3/testsuite/26_numerics/random/chi_squared_distribution/83833.cc
> deleted file mode 100644
> index 4008f7db89c..00000000000
> --- a/libstdc++-v3/testsuite/26_numerics/random/chi_squared_distribution/83833.cc
> +++ /dev/null
> @@ -1,41 +0,0 @@
> -// Copyright (C) 2018-2026 Free Software Foundation, Inc.
> -//
> -// This file is part of the GNU ISO C++ Library. This library is free
> -// software; you can redistribute it and/or modify it under the
> -// terms of the GNU General Public License as published by the
> -// Free Software Foundation; either version 3, or (at your option)
> -// any later version.
> -
> -// This library is distributed in the hope that it will be useful,
> -// but WITHOUT ANY WARRANTY; without even the implied warranty of
> -// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> -// GNU General Public License for more details.
> -
> -// You should have received a copy of the GNU General Public License along
> -// with this library; see the file COPYING3. If not see
> -// <http://www.gnu.org/licenses/>.
> -
> -// { dg-do run { target c++11 } }
> -// { dg-additional-options "-ffloat-store" { target { m68*-*-* || ia32 } } }
> -// { dg-require-cstdint "" }
> -
> -#include <random>
> -#include <testsuite_hooks.h>
> -
> -void
> -test01()
> -{
> - std::default_random_engine r1, r2;
> - using chi = std::chi_squared_distribution<double>;
> - chi::param_type p(5);
> - chi d1(p);
> - chi d2;
> - d2.param(p);
> - VERIFY( d1(r1) == d2(r2) ); // PR libstdc++/83833
> -}
> -
> -int
> -main()
> -{
> - test01();
> -}
> diff --git a/libstdc++-v3/testsuite/26_numerics/random/distribution_param.cc b/libstdc++-v3/testsuite/26_numerics/random/distribution_param.cc
> new file mode 100644
> index 00000000000..d6c06766233
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/26_numerics/random/distribution_param.cc
> @@ -0,0 +1,60 @@
> +// { dg-do run { target c++11 } }
> +// { dg-additional-options "-ffloat-store" { target { m68*-*-* || ia32 } } }
> +// { dg-require-cstdint "" }
> +
> +#include <random>
> +#include <testsuite_hooks.h>
> +
> +template<typename Distribution>
> +void
> +validate(Distribution&& source)
> +{
> + const auto& params = source.param();
> +
> + Distribution constr(params);
> + VERIFY( constr == source );
> +
> + Distribution setter;
> + setter.param(params);
> + VERIFY( setter == source );
> +
> + std::mt19937_64 e1(0x19650809ull), e2 = e1, e3 = e1;
> + for (int i = 0; i < 10; ++i)
> + {
> + const auto expected = source(e1);
> + VERIFY( constr(e2) == expected );
> + VERIFY( setter(e3) == expected );
> + }
> +}
> +
> +int main()
> +{
> + // PR83833, PR123409
> + validate(std::uniform_int_distribution<>(13, 22));
> + validate(std::uniform_real_distribution<>(1.0, 9.0));
> +
> + validate(std::bernoulli_distribution(0.478));
> + validate(std::binomial_distribution<>(7, 0.334));
> + validate(std::negative_binomial_distribution<>(726, 0.65));
> + validate(std::geometric_distribution<>(0.545));
> +
> + validate(std::poisson_distribution<>(6));
> + validate(std::exponential_distribution<>(3));
> + validate(std::gamma_distribution<>(1.1, 2.2));
> + validate(std::weibull_distribution<>(1.7, 3.0));
> + validate(std::extreme_value_distribution<>(-1.628, 1.628));
> +
> + validate(std::normal_distribution<>(5.0, 2.0));
> + validate(std::lognormal_distribution<>(1.67, 0.25));
> + validate(std::chi_squared_distribution<>(5));
> + validate(std::cauchy_distribution<>(-3, 0.25));
> + validate(std::fisher_f_distribution<>(26.0, 7.0));
> + validate(std::student_t_distribution<>(65.0));
> +
> + const auto wf = [](double x) { return 1 + x; };
> + validate(std::discrete_distribution<>(4, 1.2, 4.5, wf));
> + validate(std::piecewise_constant_distribution<>(5, 0.5, 9, wf));
> + validate(std::piecewise_linear_distribution<>(3, 1.2, 3.4, wf));
> +
> + return 0;
> +}
> --
> 2.55.0
>
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