[PATCH v2] libstdc++: Change piecewise distribution densities to return vector<result_type> [PR82749]
Tomasz Kaminski
tkaminsk@redhat.com
Mon Jun 1 08:29:16 GMT 2026
On Mon, Jun 1, 2026 at 10:16 AM Jonathan Wakely <jwakely@redhat.com> wrote:
> On Mon, 1 Jun 2026 at 08:24, Tomasz Kamiński <tkaminsk@redhat.com> wrote:
> >
> > This implements the interface changes from
> > LWG1439, "Return from densities() functions?".
> >
> > Due the ABI concerns, we cannot change the the element_type of member
> > (_M_den, _M_cp, and _M_m) vectors, and we convert the _M_den values
> > to result_type when function is invoked. However, as the usage of
> > distributions with types other than float, double, and long double
> > is either undefined (pre C++26) or implementaiton-defined (post C++26),
> > this limitation de-fact applies to float, and long double (if it's
> > different size than double).
> >
> > To handle above we introduce the __piecewise_distributions_storage<_Tp>
> > struct, whose type nested typedef points to double in above two cases,
> > and _Tp otherwise. The _StorageType is defined in terms of
> > __piecewise_distributions_storage_t alias to above, and is then used
> > in defintion of _M_den, _M_cp, and _M_m members. In consequence for
> > extended floating point types (__float128, std::float16, ...) for which
> > ABI can be changed, we store densitiees (and other values) as
> result_type.
> >
> > To avoid symbol conflicts, the param_type::densities member functions
> > are marked with "__rt" ABI tag. The corresponding members of the
> > distributions are modified to invoke param_type method, and marked
> > as always_inline. For consistency intervals methods are adjusted same
> > way.
> >
> > To preserve current behavior, the operators>> load densities
> > as values of _StorageType.
> >
> > Finally, we introduce _GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS, that
>
> This macro is spelled PICEWISE everywhere (in the commit message, the
> docs, and the code) instead of PIECEWISE.
>
> I haven't reviewed it properly yet, just noting that for now.
>
>
> > revers above changes, restoring old behavior for all floating point
> > types. Additionally for the users accept above ABI change,
> > we introduce a macro _GLIBCXX_USE_RESULT_TYPE_FOR_PIECEWISE_DENSITIES,
> > that result in __piecewise_distributions_storage_t being unconditionally
> > defined as _Tp, and thus adjust internal storage also for float and long
> > double.
> >
> > libstdc++ PR/82749
> >
> > libstdc++-v3/ChangeLog:
> >
> > * doc/xml/manual/using.xml
> > (_GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS): Add entry.
> > (_GLIBCXX_USE_RESULT_TYPE_FOR_PIECEWISE_DENSITIES): Add entry.
> > * doc/html/manual/using_macros.html: Regenerate.
> > * include/bits/random.h
> > (__detail::__piecewise_distributions_storage)
> > (__detail::__piecewise_distributions_storage_t)
> > (piecewise_constant_distribution::_StorageType)
> > (piecewise_linear_distribution::_StorageType): Define.
> > (piecewise_constant_distribution::param_type::_M_den)
> > (piecewise_constant_distribution::param_type::_M_cp)
> > (piecewise_linear_distribution::param_type::_M_den)
> > (piecewise_linear_distribution::param_type::_M_cp)
> > (piecewise_linear_distribution::param_type::_M_m): Use
> _StorageType
> > as element type.
> > (piecewise_constant_distribution::param_type::densities)
> > (piecewise_linear_distribution::param_type::densities)
> > [!_GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS]: Change return type
> > to vector<result_type>, mark with "__rt" ABI tag, and adjust
> > implementation.
> > (piecewise_constant_distribution::param_type::intervals)
> > (piecewise_linear_distribution::param_type::intervals): Use
> > result_type alias in return type.
> > (piecewise_constant_distribution::densities)
> > (piecewise_linear_distribution::densities): Delegate to
> param_type
> > method, additional change return type and mark as always_inline
> > if _GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS is not defined.
> > (piecewise_constant_distribution::intervals)
> > (piecewise_linear_distribution::intervals): Delegate to
> param_type
> > method and use result_type alias in return type.
> > * include/bits/random.tcc
> > (operator<<(basic_ostream&, const
> piecewise_constant_distribution&))
> > (operator<<(basic_ostream&, const
> piecewise_linear_distribution&)):
> > Parse vector of _StorageType for densities, to preserve behavior.
> > *
> testsuite/26_numerics/random/piecewise_constant_distribution/operators/accessors.cc:
> > New test.
> > *
> testsuite/26_numerics/random/piecewise_linear_distribution/operators/accessors.cc:
> > New test.
> > *
> testsuite/26_numerics/random/piecewise_constant_distribution/operators/accessors_exact.cc:
> > Run accessors.cc with
> _GLIBCXX_USE_RESULT_TYPE_FOR_PIECEWISE_DENSITIES.
> > *
> testsuite/26_numerics/random/piecewise_linear_distribution/operators/accessors_exact.cc:
> > Likewise.
> > *
> testsuite/26_numerics/random/piecewise_constant_distribution/operators/accessors_fallback.cc:
> > Run accessors.cc with _GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS.
> > *
> testsuite/26_numerics/random/piecewise_linear_distribution/operators/accessors_fallback.cc:
> > Likewise.
> > ---
> > v2 adds also _GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS, that
> > reverts the changes. I plan to use it for all changes made
> > to this distributions in GCC-17.
> > Additionally
> > * updates and add PR link to commit description
> > * add accessorrs_fallback.cc tests
> > * use result_type in return consistently on new path
> >
> > Resated *piecewise* test. Testing on x86_64-linux.
> > OK for trunk?
> >
> > .../doc/html/manual/using_macros.html | 19 +++
> > libstdc++-v3/doc/xml/manual/using.xml | 29 ++++
> > libstdc++-v3/include/bits/random.h | 154 +++++++++++++-----
> > libstdc++-v3/include/bits/random.tcc | 8 +-
> > .../operators/accessors.cc | 83 ++++++++++
> > .../operators/accessors_exact.cc | 5 +
> > .../operators/accessors_fallback.cc | 5 +
> > .../operators/accessors.cc | 85 ++++++++++
> > .../operators/accessors_exact.cc | 5 +
> > .../operators/accessors_fallback.cc | 5 +
> > 10 files changed, 359 insertions(+), 39 deletions(-)
> > create mode 100644
> libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/operators/accessors.cc
> > create mode 100644
> libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/operators/accessors_exact.cc
> > create mode 100644
> libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/operators/accessors_fallback.cc
> > create mode 100644
> libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/operators/accessors.cc
> > create mode 100644
> libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/operators/accessors_exact.cc
> > create mode 100644
> libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/operators/accessors_fallback.cc
> >
> > diff --git a/libstdc++-v3/doc/html/manual/using_macros.html
> b/libstdc++-v3/doc/html/manual/using_macros.html
> > index f1d8492fb9e..4be2ab576dc 100644
> > --- a/libstdc++-v3/doc/html/manual/using_macros.html
> > +++ b/libstdc++-v3/doc/html/manual/using_macros.html
> > @@ -156,4 +156,23 @@
> > <code class="option">-fexec-charset=UTF-8</code> so might give
> incorrect results
> > if called from a source file that uses a non-Unicode encoding,
> > especially for format strings using non-ASCII fill characters.
> > + </p></dd><dt><span class="term"><code
> class="code">_GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS</code></span></dt><dd><p>
> > + Undefined by default.
> > + When defined, the behaviour specializations of
> > + <code class="code">piecewise_constant_distribution</code> and
> > + <code class="code">piecewise_linear_distribution</code> for
> > + their behavior to the state prior the implementation
> > + of <a class="link" href="
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82749" target="_top">
> > + PR82749</a> (<a class="link" href="
> https://cplusplus.github.io/LWG/lwg-defects.html#1439" target="_top">
> > + LWG1439</a>) in GCC-17.
> > + </p></dd><dt><span class="term"><code
> class="code">_GLIBCXX_USE_RESULT_TYPE_FOR_PIECEWISE_DENSITIES</code></span></dt><dd><p>
> > + Undefined by default. ABI-changing.
> > + When defined, specializations of
> > + <code class="code">piecewise_constant_distribution</code> and
> > + <code class="code">piecewise_linear_distribution</code> with a
> > + <code class="code">result_type</code> of either <code
> class="code">float</code> or
> > + <code class="code">long double</code> will manage their internal
> state using
> > + <code class="code">result_type</code> values (instead of <code
> class="code">double</code>).
> > + This is required for standard conformance, but is incompatible
> with
> > + the default implementation of those class templates
> > </p></dd></dl></div></div><div class="navfooter"><hr /><table
> width="100%" summary="Navigation footer"><tr><td width="40%"
> align="left"><a accesskey="p" href="using_headers.html">Prev</a> </td><td
> width="20%" align="center"><a accesskey="u"
> href="using.html">Up</a></td><td width="40%" align="right"> <a
> accesskey="n" href="using_dual_abi.html">Next</a></td></tr><tr><td
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> align="center"><a accesskey="h" href="../index.html">Home</a></td><td
> width="40%" align="right" valign="top"> Dual
> ABI</td></tr></table></div></body></html>
> > \ No newline at end of file
> > diff --git a/libstdc++-v3/doc/xml/manual/using.xml
> b/libstdc++-v3/doc/xml/manual/using.xml
> > index e2e75e8fe28..1759eb5a214 100644
> > --- a/libstdc++-v3/doc/xml/manual/using.xml
> > +++ b/libstdc++-v3/doc/xml/manual/using.xml
> > @@ -1379,6 +1379,35 @@ g++ -Winvalid-pch -I. -include stdc++.h -H -g -O2
> hello.cc -o test.exe
> > especially for format strings using non-ASCII fill characters.
> > </para>
> > </listitem></varlistentry>
> > +
> <varlistentry><term><code>_GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS</code></term>
> > + <listitem>
> > + <para>
> > + Undefined by default.
> > + When defined, the behaviour specializations of
> > + <code>piecewise_constant_distribution</code> and
> > + <code>piecewise_linear_distribution</code> for
> > + their behavior to the state prior the implementation
> > + of <link xmlns:xlink="http://www.w3.org/1999/xlink"
> > + xlink:href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82749">
> > + PR82749</link> (<link xmlns:xlink="http://www.w3.org/1999/xlink"
> > + xlink:href="
> https://cplusplus.github.io/LWG/lwg-defects.html#1439">
> > + LWG1439</link>) in GCC-17.
> > + </para>
> > + </listitem></varlistentry>
> > +
> <varlistentry><term><code>_GLIBCXX_USE_RESULT_TYPE_FOR_PIECEWISE_DENSITIES</code></term>
> > + <listitem>
> > + <para>
> > + Undefined by default. ABI-changing.
> > + When defined, specializations of
> > + <code>piecewise_constant_distribution</code> and
> > + <code>piecewise_linear_distribution</code> with a
> > + <code>result_type</code> of either <code>float</code> or
> > + <code>long double</code> will manage their internal state using
> > + <code>result_type</code> values (instead of <code>double</code>).
> > + This is required for standard conformance, but is incompatible
> with
> > + the default implementation of those class templates
> > + </para>
> > + </listitem></varlistentry>
> > </variablelist>
> >
> > </section>
> > diff --git a/libstdc++-v3/include/bits/random.h
> b/libstdc++-v3/include/bits/random.h
> > index a0592a00763..6b82d1120b7 100644
> > --- a/libstdc++-v3/include/bits/random.h
> > +++ b/libstdc++-v3/include/bits/random.h
> > @@ -6385,6 +6385,40 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> > { return !(__d1 == __d2); }
> > #endif
> >
> > + namespace __detail
> > + {
> > +#ifdef _GLIBCXX_USE_RESULT_TYPE_FOR_PIECEWISE_DENSITIES
> > + template<typename _Tp>
> > + using __piecewise_distributions_storage_t = _Tp;
>
While fixing the name, I noticed I have this change locally, but it wasn't
included in the email.
namespace __detail
{
-#ifdef _GLIBCXX_USE_RESULT_TYPE_FOR_PIECEWISE_DENSITIES
+#if defined(_GLIBCXX_USE_OLD_PIECEWISE_DISTRIBUTIONS)
+ template<typename _Tp>
+ using __piecewise_distributions_storage_t = double;
+#elif defined(_GLIBCXX_USE_RESULT_TYPE_FOR_PIECEWISE_DENSITIES)
template<typename _Tp>
using __piecewise_distributions_storage_t = _Tp;
> > +#else
> > + template<typename _Tp>
> > + struct __piecewise_distributions_storage
> > + { using type = _Tp; };
> > +
> > + template<>
> > + struct __piecewise_distributions_storage<float>
> > + { using type = double; };
> > +
> > +# ifdef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
> > + template<>
> > + struct __piecewise_distributions_storage<__ibm128>
> > + { using type = double; };
> > +
> > + template<>
> > + struct __piecewise_distributions_storage<__ieee128>
> > + { using type = double; };
> > +# elif __LDBL_MANT_DIG__ != __DBL_MANT_DIG__
> > + template<>
> > + struct __piecewise_distributions_storage<long double>
> > + { using type = double; };
> > +# endif
> > +
> > + template<typename _Tp>
> > + using __piecewise_distributions_storage_t
> > + = typename __piecewise_distributions_storage<_Tp>::type;
> > +#endif // _GLIBCXX_USE_RESULT_TYPE_FOR_PIECEWISE_DENSITIES
> > + }
> > +
> > /**
> > * @brief A piecewise_constant_distribution random number
> distribution.
> > *
> > @@ -6407,6 +6441,9 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> > static_assert(std::is_floating_point<_RealType>::value,
> > "result_type must be a floating point type");
> >
> > + using _StorageType
> > + = __detail::__piecewise_distributions_storage_t<_RealType>;
> > +
> > public:
> > /** The type of the range of the distribution. */
> > typedef _RealType result_type;
> > @@ -6437,7 +6474,7 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> > param_type(const param_type&) = default;
> > param_type& operator=(const param_type&) = default;
> >
> > - std::vector<_RealType>
> > + std::vector<result_type>
> > intervals() const
> > {
> > if (_M_int.empty())
> > @@ -6450,9 +6487,34 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> > return _M_int;
> > }
> >
> > +#ifdef _GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS
> > std::vector<double>
> > densities() const
> > { return _M_den.empty() ? std::vector<double>(1, 1.0) : _M_den; }
> > +#else
> > + // _GLIBCXX_RESOLVE_LIB_DEFECTS
> > + // 1439. Return from densities() functions?
> > + [[__gnu__::__abi_tag__("__rt")]]
> > + std::vector<result_type>
> > + densities() const
> > + {
> > +#pragma GCC diagnostic push
> > +#pragma GCC diagnostic ignored "-Wc++17-extensions"
> > + if (_M_den.empty())
> > + return std::vector<_RealType>(1, _RealType(1));
> > + else if constexpr (is_same<_RealType, _StorageType>::value)
> > + return _M_den;
> > + else
> > + {
> > + std::vector<_RealType> __res;
> > + __res.reserve(_M_den.size());
> > + for (_RealType __v : _M_den)
> > + __res.push_back(__v);
> > + return __res;
> > + }
> > +#pragma GCC diagnostic pop
> > + }
> > +#endif
> >
> > friend bool
> > operator==(const param_type& __p1, const param_type& __p2)
> > @@ -6472,8 +6534,8 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> > _M_initialize2(const _RealType* __ints, _RealType __den);
> >
> > std::vector<_RealType> _M_int;
> > - std::vector<double> _M_den;
> > - std::vector<double> _M_cp;
> > + std::vector<_StorageType> _M_den;
> > + std::vector<_StorageType> _M_cp;
> >
> > template<typename _RealType1, typename _CharT, typename _Traits>
> > friend std::basic_ostream<_CharT, _Traits>&
> > @@ -6520,28 +6582,23 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> > /**
> > * @brief Returns a vector of the intervals.
> > */
> > - std::vector<_RealType>
> > + std::vector<result_type>
> > intervals() const
> > - {
> > - if (_M_param._M_int.empty())
> > - {
> > - std::vector<_RealType> __tmp(2);
> > - __tmp[1] = _RealType(1);
> > - return __tmp;
> > - }
> > - else
> > - return _M_param._M_int;
> > - }
> > + { return _M_param.intervals(); }
> >
> > /**
> > * @brief Returns a vector of the probability densities.
> > */
> > +#ifdef _GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS
> > std::vector<double>
> > densities() const
> > - {
> > - return _M_param._M_den.empty()
> > - ? std::vector<double>(1, 1.0) : _M_param._M_den;
> > - }
> > + { return _M_param.densities(); }
> > +#else
> > + [[__gnu__::__always_inline__]]
> > + std::vector<result_type>
> > + densities() const
> > + { return _M_param.densities(); }
> > +#endif
> >
> > /**
> > * @brief Returns the parameter set of the distribution.
> > @@ -6695,6 +6752,9 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> > static_assert(std::is_floating_point<_RealType>::value,
> > "result_type must be a floating point type");
> >
> > + using _StorageType
> > + = __detail::__piecewise_distributions_storage_t<_RealType>;
> > +
> > public:
> > /** The type of the range of the distribution. */
> > typedef _RealType result_type;
> > @@ -6725,7 +6785,7 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> > param_type(const param_type&) = default;
> > param_type& operator=(const param_type&) = default;
> >
> > - std::vector<_RealType>
> > + std::vector<result_type>
> > intervals() const
> > {
> > if (_M_int.empty())
> > @@ -6738,9 +6798,34 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> > return _M_int;
> > }
> >
> > +#ifdef _GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS
> > std::vector<double>
> > densities() const
> > { return _M_den.empty() ? std::vector<double>(2, 1.0) : _M_den; }
> > +#else
> > + // _GLIBCXX_RESOLVE_LIB_DEFECTS
> > + // 1439. Return from densities() functions?
> > + [[__gnu__::__abi_tag__("__rt")]]
> > + std::vector<result_type>
> > + densities() const
> > + {
> > +#pragma GCC diagnostic push
> > +#pragma GCC diagnostic ignored "-Wc++17-extensions"
> > + if (_M_den.empty())
> > + return std::vector<_RealType>(2, _RealType(1));
> > + else if constexpr (is_same<_RealType, _StorageType>::value)
> > + return _M_den;
> > + else
> > + {
> > + std::vector<_RealType> __res;
> > + __res.reserve(_M_den.size());
> > + for (_RealType __v : _M_den)
> > + __res.push_back(__v);
> > + return __res;
> > + }
> > +#pragma GCC diagnostic pop
> > + }
> > +#endif
> >
> > friend bool
> > operator==(const param_type& __p1, const param_type& __p2)
> > @@ -6760,9 +6845,9 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> > _M_initialize2(const _RealType* __ints, const _RealType* __dens);
> >
> > std::vector<_RealType> _M_int;
> > - std::vector<double> _M_den;
> > - std::vector<double> _M_cp;
> > - std::vector<double> _M_m;
> > + std::vector<_StorageType> _M_den;
> > + std::vector<_StorageType> _M_cp;
> > + std::vector<_StorageType> _M_m;
> >
> > template<typename _RealType1, typename _CharT, typename _Traits>
> > friend std::basic_ostream<_CharT, _Traits>&
> > @@ -6809,29 +6894,24 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> > /**
> > * @brief Return the intervals of the distribution.
> > */
> > - std::vector<_RealType>
> > + std::vector<result_type>
> > intervals() const
> > - {
> > - if (_M_param._M_int.empty())
> > - {
> > - std::vector<_RealType> __tmp(2);
> > - __tmp[1] = _RealType(1);
> > - return __tmp;
> > - }
> > - else
> > - return _M_param._M_int;
> > - }
> > + { return _M_param.intervals(); }
> >
> > /**
> > * @brief Return a vector of the probability densities of the
> > * distribution.
> > */
> > +#ifdef _GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS
> > std::vector<double>
> > densities() const
> > - {
> > - return _M_param._M_den.empty()
> > - ? std::vector<double>(2, 1.0) : _M_param._M_den;
> > - }
> > + { return _M_param.densities(); }
> > +#else
> > + [[__gnu__::__always_inline__]]
> > + std::vector<result_type>
> > + densities() const
> > + { return _M_param.densities(); }
> > +#endif
> >
> > /**
> > * @brief Returns the parameter set of the distribution.
> > diff --git a/libstdc++-v3/include/bits/random.tcc
> b/libstdc++-v3/include/bits/random.tcc
> > index e581f912764..6c88d68d3e4 100644
> > --- a/libstdc++-v3/include/bits/random.tcc
> > +++ b/libstdc++-v3/include/bits/random.tcc
> > @@ -3199,6 +3199,8 @@ namespace __detail
> > piecewise_constant_distribution<_RealType>& __x)
> > {
> > using __ios_base = typename basic_istream<_CharT,
> _Traits>::ios_base;
> > + using _StorageType
> > + = typename
> piecewise_constant_distribution<_RealType>::_StorageType;
> >
> > const typename __ios_base::fmtflags __flags = __is.flags();
> > __is.flags(__ios_base::dec | __ios_base::skipws);
> > @@ -3209,7 +3211,7 @@ namespace __detail
> > std::vector<_RealType> __int_vec;
> > if (__detail::__extract_params(__is, __int_vec, __n + 1))
> > {
> > - std::vector<double> __den_vec;
> > + std::vector<_StorageType> __den_vec;
> > if (__detail::__extract_params(__is, __den_vec, __n))
> > {
> > __x.param({ __int_vec.begin(), __int_vec.end(),
> > @@ -3466,6 +3468,8 @@ namespace __detail
> > piecewise_linear_distribution<_RealType>& __x)
> > {
> > using __ios_base = typename basic_istream<_CharT,
> _Traits>::ios_base;
> > + using _StorageType
> > + = typename
> piecewise_linear_distribution<_RealType>::_StorageType;
> >
> > const typename __ios_base::fmtflags __flags = __is.flags();
> > __is.flags(__ios_base::dec | __ios_base::skipws);
> > @@ -3476,7 +3480,7 @@ namespace __detail
> > vector<_RealType> __int_vec;
> > if (__detail::__extract_params(__is, __int_vec, __n + 1))
> > {
> > - vector<double> __den_vec;
> > + vector<_StorageType> __den_vec;
> > if (__detail::__extract_params(__is, __den_vec, __n + 1))
> > {
> > __x.param({ __int_vec.begin(), __int_vec.end(),
> > diff --git
> a/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/operators/accessors.cc
> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/operators/accessors.cc
> > new file mode 100644
> > index 00000000000..219d1949040
> > --- /dev/null
> > +++
> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/operators/accessors.cc
> > @@ -0,0 +1,83 @@
> > +// { dg-do run { target c++11 } }
> > +// { dg-require-cstdint "" }
> > +
> > +#include <random>
> > +#include <testsuite_hooks.h>
> > +
> > +template<typename RealType>
> > +void
> > +test_exact()
> > +{
> > + RealType x[6] = {0.0, 1.0, 2.0, 3.0, 4.0, 5.0};
> > + RealType wt[5] = {0.5, 1.0, 3.5, 2.5, 0.5};
> > +
> > + std::piecewise_constant_distribution<RealType>
> > + u(std::begin(x), std::end(x), wt);
> > +
> > + const std::vector<RealType>& interval = u.intervals();
> > + VERIFY( interval.size() == 6 );
> > + VERIFY( interval[0] == RealType(0.0) );
> > + VERIFY( interval[5] == RealType(5.0) );
> > +
> > +#ifdef _GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS
> > + const std::vector<double>& density = u.densities();
> > +#else
> > + const std::vector<RealType>& density = u.densities();
> > +#endif
> > +
> > + VERIFY( density.size() == 5 );
> > + VERIFY( density[0] == RealType(0.5 / 8.0) );
> > + VERIFY( density[1] == RealType(1.0 / 8.0) );
> > + VERIFY( density[2] == RealType(3.5 / 8.0) );
> > + VERIFY( density[3] == RealType(2.5 / 8.0) );
> > + VERIFY( density[4] == RealType(0.5 / 8.0) );
> > +}
> > +
> > +template<typename RealType>
> > +void
> > +test_precision_depended()
> > +{
> > + constexpr bool preserved
> > +#ifdef _GLIBCXX_USE_RESULT_TYPE_FOR_PIECEWISE_DENSITIES
> > + = true;
> > +#else
> > + = sizeof(RealType) <= sizeof(double);
> > +#endif
> > +
> > + RealType x[3]{0.0, 0.5, 1.0};
> > + constexpr RealType step
> > + = std::numeric_limits<RealType>::epsilon();
> > + RealType wt[2]{RealType(1) - step, RealType(1) + step};
> > +
> > + std::piecewise_constant_distribution<RealType>
> > + u(std::begin(x), std::end(x), wt);
> > +
> > + const std::vector<RealType>& interval = u.intervals();
> > + VERIFY( interval.size() == 3 );
> > + VERIFY( interval[0] == RealType(0.0) );
> > + VERIFY( interval[2] == RealType(1.0) );
> > +
> > +#ifdef _GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS
> > + const std::vector<double>& density = u.densities();
> > +#else
> > + const std::vector<RealType>& density = u.densities();
> > +#endif
> > +
> > + VERIFY( density.size() == 2 );
> > + VERIFY( density[0] == (preserved ? wt[0] : RealType(1)) );
> > + VERIFY( density[1] == (preserved ? wt[1] : RealType(1)) );
> > +}
> > +
> > +int main()
> > +{
> > + using namespace __gnu_test;
> > + test_exact<float>();
> > + test_exact<double>();
> > + test_exact<long double>();
> > +
> > + test_precision_depended<float>();
> > + test_precision_depended<double>();
> > + test_precision_depended<long double>();
> > +
> > + return 0;
> > +}
> > diff --git
> a/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/operators/accessors_exact.cc
> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/operators/accessors_exact.cc
> > new file mode 100644
> > index 00000000000..469ed3fac46
> > --- /dev/null
> > +++
> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/operators/accessors_exact.cc
> > @@ -0,0 +1,5 @@
> > +// { dg-options "-D_GLIBCXX_USE_RESULT_TYPE_FOR_PIECEWISE_DENSITIES" }
> > +// { dg-do run { target c++11 } }
> > +// { dg-require-cstdint "" }
> > +#include "accessors.cc"
> > +
> > diff --git
> a/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/operators/accessors_fallback.cc
> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/operators/accessors_fallback.cc
> > new file mode 100644
> > index 00000000000..3e2fbf03430
> > --- /dev/null
> > +++
> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/operators/accessors_fallback.cc
> > @@ -0,0 +1,5 @@
> > +// { dg-options "-D_GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS" }
> > +// { dg-do run { target c++11 } }
> > +// { dg-require-cstdint "" }
> > +#include "accessors.cc"
> > +
> > diff --git
> a/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/operators/accessors.cc
> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/operators/accessors.cc
> > new file mode 100644
> > index 00000000000..d3855ee0291
> > --- /dev/null
> > +++
> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/operators/accessors.cc
> > @@ -0,0 +1,85 @@
> > +// { dg-do run { target c++11 } }
> > +// { dg-require-cstdint "" }
> > +
> > +#include <random>
> > +#include <testsuite_hooks.h>
> > +
> > +template<typename RealType>
> > +void
> > +test_exact()
> > +{
> > + RealType x[6] = {0.0, 1.0, 2.0, 3.0, 4.0, 5.0};
> > + RealType wt[6] = {0.0, 1.0, 1.0, 6.0, -1.0, 2.0};
> > +
> > + std::piecewise_linear_distribution<RealType>
> > + u(std::begin(x), std::end(x), wt);
> > +
> > + const std::vector<RealType>& interval = u.intervals();
> > + VERIFY( interval.size() == 6 );
> > + VERIFY( interval[0] == RealType(0.0) );
> > + VERIFY( interval[5] == RealType(5.0) );
> > +
> > +#ifdef _GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS
> > + const std::vector<double>& density = u.densities();
> > +#else
> > + const std::vector<RealType>& density = u.densities();
> > +#endif
> > +
> > + VERIFY( density.size() == 6 );
> > + VERIFY( density[0] == RealType(0.0 / 8.0) );
> > + VERIFY( density[1] == RealType(1.0 / 8.0) );
> > + VERIFY( density[2] == RealType(1.0 / 8.0) );
> > + VERIFY( density[3] == RealType(6.0 / 8.0) );
> > + VERIFY( density[4] == RealType(-1.0 / 8.0) );
> > + VERIFY( density[5] == RealType(2.0 / 8.0) );
> > +}
> > +
> > +template<typename RealType>
> > +void
> > +test_precision_depended()
> > +{
> > + constexpr bool preserved
> > +#ifdef _GLIBCXX_USE_RESULT_TYPE_FOR_PIECEWISE_DENSITIES
> > + = true;
> > +#else
> > + = sizeof(RealType) <= sizeof(double);
> > +#endif
> > +
> > + RealType x[3]{0.0, 0.5, 1.0};
> > + constexpr RealType step
> > + = std::numeric_limits<RealType>::epsilon() * 2;
> > + RealType wt[3]{RealType(1) - step, RealType(1), RealType(1) + step};
> > +
> > + std::piecewise_linear_distribution<RealType>
> > + u(std::begin(x), std::end(x), wt);
> > +
> > + const std::vector<RealType>& interval = u.intervals();
> > + VERIFY( interval.size() == 3 );
> > + VERIFY( interval[0] == RealType(0.0) );
> > + VERIFY( interval[2] == RealType(1.0) );
> > +
> > +#ifdef _GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS
> > + const std::vector<double>& density = u.densities();
> > +#else
> > + const std::vector<RealType>& density = u.densities();
> > +#endif
> > +
> > + VERIFY( density.size() == 3 );
> > + VERIFY( density[0] == (preserved ? wt[0] : RealType(1)) );
> > + VERIFY( density[1] == RealType(1) );
> > + VERIFY( density[2] == (preserved ? wt[2] : RealType(1)) );
> > +}
> > +
> > +int main()
> > +{
> > + using namespace __gnu_test;
> > + test_exact<float>();
> > + test_exact<double>();
> > + test_exact<long double>();
> > +
> > + test_precision_depended<float>();
> > + test_precision_depended<double>();
> > + test_precision_depended<long double>();
> > +
> > + return 0;
> > +}
> > diff --git
> a/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/operators/accessors_exact.cc
> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/operators/accessors_exact.cc
> > new file mode 100644
> > index 00000000000..469ed3fac46
> > --- /dev/null
> > +++
> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/operators/accessors_exact.cc
> > @@ -0,0 +1,5 @@
> > +// { dg-options "-D_GLIBCXX_USE_RESULT_TYPE_FOR_PIECEWISE_DENSITIES" }
> > +// { dg-do run { target c++11 } }
> > +// { dg-require-cstdint "" }
> > +#include "accessors.cc"
> > +
> > diff --git
> a/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/operators/accessors_fallback.cc
> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/operators/accessors_fallback.cc
> > new file mode 100644
> > index 00000000000..3e2fbf03430
> > --- /dev/null
> > +++
> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/operators/accessors_fallback.cc
> > @@ -0,0 +1,5 @@
> > +// { dg-options "-D_GLIBCXX_USE_OLD_PICEWISE_DISTRIBUTIONS" }
> > +// { dg-do run { target c++11 } }
> > +// { dg-require-cstdint "" }
> > +#include "accessors.cc"
> > +
> > --
> > 2.54.0
> >
>
>
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