[{"id":3684715,"web_url":"http://patchwork.ozlabs.org/comment/3684715/","msgid":"<CAKvuMXB38DJ8CyYfxf6+CUptjL9z+LBzAOZHDgYNq19k06o_5g@mail.gmail.com>","list_archive_url":null,"date":"2026-04-30T13:53:48","subject":"Re: [PATCH] libstdc++: Fix reserve of size_t(-1) elements in\n piecewise_constant_distribution. [PR113761]","submitter":{"id":90409,"url":"http://patchwork.ozlabs.org/api/people/90409/","name":"Tomasz Kamiński","email":"tkaminsk@redhat.com"},"content":"On Thu, Apr 30, 2026 at 1:04 PM Tomasz Kamiński <tkaminsk@redhat.com> wrote:\n\n> The piecewise_constant_distribution constructor from std::initializer_list\n> il,\n> unconditionally _M_den reserved il.size()-1 elements. In case when the\n> il.size()\n> was zero, this led to unsigned overflow, and attempt to allocate size_t(-1)\n> elements.\n>\n> This patch addresses above, by refactoring the constructors of param_type\n> for\n> both piecewise_constant_distribution and piecewise_linear_distribution, to\n> exit early (and do not populate internal vectors) if number of intervals\n> range is\n> smaller than two. For the constructor accepting pair of iterators, this is\n> done\n> by checking result of __detail::__load_first2, that extracts up to two\n> elements,\n> and returns false, if less than two is found.\n>\n> Futhremore, we if the number of intervals is equal to two (for iterator\n> __bbegin\n> is at __bend after __load_first2), we store densities value on stack, and\n> call\n> newly introduced an _M_initialize2 helper, that does not popluate internal\n> vector\n> if __ints and __dens values correspond to default configuration.\n>\n> With both of above changes, we no longer populate _M_int and _M_den with\n> default\n> values, and corresponding code that clears them in _M_initialize is not\n> necessary.\n> This avoids any uncessary memory allocatos.\n>\n> Finally, for constructor accepting two iterators, we reserve required space\n> in _M_int vector, if the iterators are forward (or model sized_sentinel in\n> C++20).\n> The _M_den initialization is performed afterwards, so _M_ints size is\n> already\n> determined (even for input iterators) and it can be used for call to\n> reserve.\n>\n>         PR libstdc++/113761\n>\n> libstdc++-v3/ChangeLog:\n>\n>         * include/bits/random.h\n>         (piecewise_constant_distribution::param_type::_M_initialize2)\n>         (piecewise_linear_distribution::param_type::_M_initialize2):\n> Declare.\n>         * include/bits/random.tcc (__detail::__load_first2): Define.\n>         (piecewise_constant_distribution::param_type::_M_initialize)\n>         (piecewise_linear_distribution::param_type::_M_initialize):\n>         Remove checks for default values.\n>         (piecewise_constant_distribution::param_type::_M_initialize2)\n>         (piecewise_linear_distribution::param_type::_M_initialize2):\n> Define.\n>         (piecewise_constant_distribution::param_type::param_type)\n>         (piecewise_linear_distribution::param_type::param_type):\n>         Exit early for less that two intervals. Use _M_initialize2 to\n> handle\n>         two intervals case. Reserve _M_int for iterators case.\n>         *\n> testsuite/26_numerics/random/piecewise_constant_distribution/cons/range.cc:\n>         Test input and forward iterators, in addition to random_access\n> ones.\n>         *\n> testsuite/26_numerics/random/piecewise_linear_distribution/cons/range.cc:\n>         Likewise.\n>         *\n> testsuite/26_numerics/random/piecewise_constant_distribution/cons/fallback.cc:\n>         New test.\n>         *\n> testsuite/26_numerics/random/piecewise_linear_distribution/cons/fallback.cc:\n>         New test.\n> ---\n> Tested on x86_64-linux locally. *piecewise* tests additionally tested\n> with all standard modes and modules. OK for trunk?\n>\n>  libstdc++-v3/include/bits/random.h            |   6 +\n>  libstdc++-v3/include/bits/random.tcc          | 208 ++++++++++++++----\n>  .../cons/fallback.cc                          | 108 +++++++++\n>  .../cons/range.cc                             |  17 +-\n>  .../cons/fallback.cc                          | 127 +++++++++++\n>  .../cons/range.cc                             |  17 +-\n>  6 files changed, 429 insertions(+), 54 deletions(-)\n>  create mode 100644\n> libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/cons/fallback.cc\n>  create mode 100644\n> libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/cons/fallback.cc\n>\n> diff --git a/libstdc++-v3/include/bits/random.h\n> b/libstdc++-v3/include/bits/random.h\n> index 3fda69c4399..d8125bb0f62 100644\n> --- a/libstdc++-v3/include/bits/random.h\n> +++ b/libstdc++-v3/include/bits/random.h\n> @@ -6468,6 +6468,9 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)\n>         void\n>         _M_initialize();\n>\n> +       void\n> +       _M_initialize2(const _RealType* __ints, _RealType __den);\n> +\n>         std::vector<_RealType> _M_int;\n>         std::vector<double> _M_den;\n>         std::vector<double> _M_cp;\n> @@ -6748,6 +6751,9 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)\n>         void\n>         _M_initialize();\n>\n> +       void\n> +       _M_initialize2(const _RealType* __ints, const _RealType *__dens);\n> +\n>         std::vector<_RealType> _M_int;\n>         std::vector<double> _M_den;\n>         std::vector<double> _M_cp;\n> diff --git a/libstdc++-v3/include/bits/random.tcc\n> b/libstdc++-v3/include/bits/random.tcc\n> index 4475e365c2d..8d4e46c5168 100644\n> --- a/libstdc++-v3/include/bits/random.tcc\n> +++ b/libstdc++-v3/include/bits/random.tcc\n> @@ -2947,16 +2947,6 @@ namespace __detail\n>      piecewise_constant_distribution<_RealType>::param_type::\n>      _M_initialize()\n>      {\n> -      if (_M_int.size() < 2\n> -         || (_M_int.size() == 2\n> -             && _M_int[0] == _RealType(0)\n> -             && _M_int[1] == _RealType(1)))\n> -       {\n> -         _M_int.clear();\n> -         _M_den.clear();\n> -         return;\n> -       }\n> -\n>        const double __sum = std::accumulate(_M_den.begin(),\n>                                            _M_den.end(), 0.0);\n>        __glibcxx_assert(__sum > 0);\n> @@ -2975,6 +2965,46 @@ namespace __detail\n>         _M_den[__k] /= _M_int[__k + 1] - _M_int[__k];\n>      }\n>\n> +  template<typename _RealType>\n> +    void\n> +    piecewise_constant_distribution<_RealType>::param_type::\n> +    _M_initialize2(const _RealType *__ints, _RealType __den)\n> +    {\n> +      if (__ints[0] == _RealType(0) && __ints[1] == _RealType(1))\n> +       return;\n> +\n> +      _M_int.reserve(2);\n> +      _M_int.push_back(__ints[0]);\n> +      _M_int.push_back(__ints[1]);\n> +\n> +      _M_den.reserve(1);\n> +      _M_den.push_back(__den);\n> +      _M_initialize();\n> +    }\n> +\n> +namespace __detail\n> +{\n> +  template<typename _InputIterator, typename _RealType>\n> +    bool\n> +    __load_first2(_InputIterator& __first, _InputIterator __last,\n> +                 _RealType* __out)\n> +    {\n> +      if (__first == __last)\n> +       return false;\n> +\n> +      *__out = *__first;\n> +      ++__first;\n> +      if (__first == __last)\n> +       return false;\n> +\n> +      ++__out;\n> +      *__out = *__first;\n> +      ++__first;\n> +      return true;\n> +    }\n> +} // namespace __detail\n> +\n> +\n>    template<typename _RealType>\n>      template<typename _InputIteratorB, typename _InputIteratorW>\n>        piecewise_constant_distribution<_RealType>::param_type::\n> @@ -2983,20 +3013,38 @@ namespace __detail\n>                  _InputIteratorW __wbegin)\n>        : _M_int(), _M_den(), _M_cp()\n>        {\n> -       if (__bbegin != __bend)\n> -         {\n> -           for (;;)\n> -             {\n> -               _M_int.push_back(*__bbegin);\n> -               ++__bbegin;\n> -               if (__bbegin == __bend)\n> -                 break;\n> +       _RealType __ints[2];\n> +       if (!__detail::__load_first2(__bbegin, __bend, __ints))\n> +         return;\n>\n> -               _M_den.push_back(*__wbegin);\n> -               ++__wbegin;\n> -             }\n> +       if (__bbegin == __bend)\n> +         {\n> +           _M_initialize2(__ints, *__wbegin);\n> +           return;\n>           }\n>\n> +#if __glibcxx_concepts // C++ >= C++20\n> +       if constexpr (sized_sentinel_for<_InputIteratorB, _InputIteratorB>\n> +                       || forward_iterator<_InputIteratorB>)\n> +         _M_int.reserve(2 + size_t(ranges::distance(__bbegin, __bend)));\n> +#else\n> +#pragma GCC diagnostic push\n> +#pragma GCC diagnostic ignored \"-Wc++17-extensions\" // if constexpr\n> +       if constexpr (is_convertible<__iter_category_t<_InputIteratorB>,\n> +                                    forward_iterator_tag>::value)\n> +         _M_int.reserve(2 + size_t(std::distance(__bbegin, __bend)));\n> +#pragma GCC diagnostic pop\n> +#endif\n> +\n> +       _M_int.push_back(__ints[0]);\n> +       _M_int.push_back(__ints[1]);\n> +       for (; __bbegin != __bend; ++__bbegin)\n> +         _M_int.push_back(*__bbegin);\n> +\n> +       _M_den.reserve(_M_int.size() - 1);\n> +       for (size_t __k = 0; __k < _M_int.size() - 1; (void)++__k,\n> ++__wbegin)\n> +         _M_den.push_back(*__wbegin);\n> +\n>         _M_initialize();\n>        }\n>\n> @@ -3006,10 +3054,18 @@ namespace __detail\n>        param_type(initializer_list<_RealType> __bl, _Func __fw)\n>        : _M_int(), _M_den(), _M_cp()\n>        {\n> -       _M_int.reserve(__bl.size());\n> -       for (auto __biter = __bl.begin(); __biter != __bl.end(); ++__biter)\n> -         _M_int.push_back(*__biter);\n> +       if (__bl.size() < 2)\n> +         return;\n> +\n> +       if (__bl.size() == 2)\n> +         {\n> +           const _RealType *__ints = __bl.begin();\n> +           _RealType __den = __fw(0.5 * (__ints[1] + __ints[0]));\n> +           _M_initialize2(__ints, __den);\n> +           return;\n> +         }\n>\n> +       _M_int = __bl;\n>         _M_den.reserve(_M_int.size() - 1);\n>         for (size_t __k = 0; __k < _M_int.size() - 1; ++__k)\n>           _M_den.push_back(__fw(0.5 * (_M_int[__k + 1] + _M_int[__k])));\n> @@ -3025,6 +3081,13 @@ namespace __detail\n>        {\n>         const size_t __n = __nw == 0 ? 1 : __nw;\n>         const _RealType __delta = (__xmax - __xmin) / __n;\n> +       if (__n == 1)\n> +         {\n> +           _RealType __ints[2] = { __xmin, __xmin + __delta };\n> +           _RealType __den = __fw(__xmin * 0.5 * __delta);\n> +           _M_initialize2(__ints, __den);\n> +           return;\n> +         }\n>\n>         _M_int.reserve(__n + 1);\n>         for (size_t __k = 0; __k <= __nw; ++__k)\n> @@ -3161,17 +3224,6 @@ namespace __detail\n>      piecewise_linear_distribution<_RealType>::param_type::\n>      _M_initialize()\n>      {\n> -      if (_M_int.size() < 2\n> -         || (_M_int.size() == 2\n> -             && _M_int[0] == _RealType(0)\n> -             && _M_int[1] == _RealType(1)\n> -             && _M_den[0] == _M_den[1]))\n> -       {\n> -         _M_int.clear();\n> -         _M_den.clear();\n> -         return;\n> -       }\n> -\n>        double __sum = 0.0;\n>        _M_cp.reserve(_M_int.size() - 1);\n>        _M_m.reserve(_M_int.size() - 1);\n> @@ -3194,7 +3246,27 @@ namespace __detail\n>\n>        //  Make sure the last cumulative probablility is one.\n>        _M_cp[_M_cp.size() - 1] = 1.0;\n> -     }\n> +    }\n> +\n> +  template<typename _RealType>\n> +    void\n> +    piecewise_linear_distribution<_RealType>::param_type::\n> +    _M_initialize2(const _RealType *__ints, const _RealType* __dens)\n> +    {\n> +      if (__ints[0] == _RealType(0)\n> +         && __ints[1] == _RealType(1)\n> +         && __dens[0] == __dens[1])\n> +       return;\n> +\n> +      _M_int.reserve(2);\n> +      _M_int.push_back(__ints[0]);\n> +      _M_int.push_back(__ints[1]);\n> +\n> +      _M_den.reserve(2);\n> +      _M_den.push_back(__dens[0]);\n> +      _M_den.push_back(__dens[1]);\n> +      _M_initialize();\n> +    }\n>\n>    template<typename _RealType>\n>      template<typename _InputIteratorB, typename _InputIteratorW>\n> @@ -3204,12 +3276,42 @@ namespace __detail\n>                  _InputIteratorW __wbegin)\n>        : _M_int(), _M_den(), _M_cp(), _M_m()\n>        {\n> -       for (; __bbegin != __bend; ++__bbegin, (void) ++__wbegin)\n> +       _RealType __ints[2];\n> +       if (!__detail::__load_first2(__bbegin, __bend, __ints))\n> +         return;\n> +\n> +       if (__bbegin == __bend)\n>           {\n> -           _M_int.push_back(*__bbegin);\n> -           _M_den.push_back(*__wbegin);\n> +           _RealType __dens[2];\n> +           __dens[0] = *__wbegin;\n> +           ++__wbegin;\n> +           __dens[1] = *__wbegin;\n> +           _M_initialize2(__ints, __dens);\n> +           return;\n>           }\n>\n> +#if __glibcxx_concepts // C++ >= C++20\n> +       if constexpr (sized_sentinel_for<_InputIteratorB, _InputIteratorB>\n> +                       || forward_iterator<_InputIteratorB>)\n> +         _M_int.reserve(2 + size_t(ranges::distance(__bbegin, __bend)));\n> +#else\n> +#pragma GCC diagnostic push\n> +#pragma GCC diagnostic ignored \"-Wc++17-extensions\" // if constexpr\n> +       if constexpr (is_convertible<__iter_category_t<_InputIteratorB>,\n> +                                    forward_iterator_tag>::value)\n> +         _M_int.reserve(2 + size_t(std::distance(__bbegin, __bend)));\n> +#pragma GCC diagnostic pop\n> +#endif\n> +\n> +       _M_int.push_back(__ints[0]);\n> +       _M_int.push_back(__ints[1]);\n> +       for (; __bbegin != __bend; ++__bbegin)\n> +         _M_int.push_back(*__bbegin);\n> +\n> +       _M_den.reserve(_M_int.size());\n> +       for (size_t __i = 0; __i < _M_int.size(); (void)++__i, ++__wbegin)\n> +         _M_den.push_back(*__wbegin);\n> +\n>         _M_initialize();\n>        }\n>\n> @@ -3219,14 +3321,23 @@ namespace __detail\n>        param_type(initializer_list<_RealType> __bl, _Func __fw)\n>        : _M_int(), _M_den(), _M_cp(), _M_m()\n>        {\n> -       _M_int.reserve(__bl.size());\n> -       _M_den.reserve(__bl.size());\n> -       for (auto __biter = __bl.begin(); __biter != __bl.end(); ++__biter)\n> +       if (__bl.size() < 2)\n> +         return;\n> +\n> +       if (__bl.size() == 2)\n>           {\n> -           _M_int.push_back(*__biter);\n> -           _M_den.push_back(__fw(*__biter));\n> +           const _RealType *__ints = __bl.begin();\n> +           _RealType __den[2];\n> +           __den[0] = __fw(__ints[0]);\n> +           __den[1] = __fw(__ints[1]);\n> +           _M_initialize2(__ints, __den);\n> +           return;\n>           }\n>\n> +       _M_int = __bl;\n> +       _M_den.reserve(__bl.size());\n> +       for (auto __biter = __bl.begin(); __biter != __bl.end(); ++__biter)\n> +           _M_den.push_back(__fw(*__biter));\n>         _M_initialize();\n>        }\n>\n> @@ -3238,6 +3349,15 @@ namespace __detail\n>        {\n>         const size_t __n = __nw == 0 ? 1 : __nw;\n>         const _RealType __delta = (__xmax - __xmin) / __n;\n> +       if (__n == 1)\n> +         {\n> +           _RealType __ints[2] = { __xmin, __xmin + __delta };\n> +           _RealType __dens[2];\n> +           __dens[0] = __fw(__ints[0]);\n> +           __dens[1] = __fw(__ints[1]);\n> +           _M_initialize2(__ints, __dens);\n> +           return;\n> +         }\n>\n>         _M_int.reserve(__n + 1);\n>         _M_den.reserve(__n + 1);\n> diff --git\n> a/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/cons/fallback.cc\n> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/cons/fallback.cc\n> new file mode 100644\n> index 00000000000..1917e69972a\n> --- /dev/null\n> +++\n> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/cons/fallback.cc\n> @@ -0,0 +1,108 @@\n> +// { dg-do run { target c++11 } }\n> +// { dg-require-cstdint \"\" }\n> +\n> +#include <random>\n> +#include <testsuite_hooks.h>\n> +#include <testsuite_iterators.h>\n> +\n> +using dist = std::piecewise_linear_distribution<>;\n> +\n> +template<typename... Args>\n> +bool\n> +is_default(Args&&... args)\n> +{\n> +  std::piecewise_constant_distribution<> u(std::forward<Args>(args)...);\n> +\n> +  std::vector<double> ints = u.intervals();\n> +  if (ints.size() != 2 || ints[0] != 0.0 || ints[1] != 1.0)\n> +    return false;\n> +\n> +  std::vector<double> dens = u.densities();\n> +  if (dens.size() != 1 || dens[0] != 1.0)\n> +    return false;\n> +\n> +  return true;\n> +}\n> +\n> +template<template<typename> class Range>\n> +void\n> +test_it_pair()\n> +{\n> +  double wt[2];\n> +  double x[3];\n> +\n> +  Range<double> r0(x, x);\n> +  VERIFY( is_default(r0.begin(), r0.end(), wt) );\n> +\n> +  x[0] = 4.2;\n> +  Range<double> r1a(x, x+1);\n> +  VERIFY( is_default(r1a.begin(), r1a.end(), wt) );\n> +\n> +  x[0] = 0.0;\n> +  Range<double> r1b(x, x+1);\n> +  VERIFY( is_default(r1b.begin(), r1b.end(), wt) );\n> +\n> +  x[1] = 1.0;\n> +  wt[0] = 13.0;\n> +  Range<double> r2a(x, x+2);\n> +  VERIFY( is_default(r2a.begin(), r2a.end(), wt) );\n> +\n> +  wt[0] = 4.2;\n> +  Range<double> r2b(x, x+2);\n> +  VERIFY( is_default(r2b.begin(), r2b.end(), wt) );\n> +\n> +  x[1] = 0.5;\n> +  Range<double> r2c(x, x+2);\n> +  VERIFY( !is_default(r2c.begin(), r2c.end(), wt) );\n> +\n> +  x[2] = 1.0;\n> +  wt[1] = 2.0;\n> +  Range<double> r3(x, x+3);\n> +  VERIFY( !is_default(r3.begin(), r3.end(), wt) );\n> +}\n> +\n> +void test_init_list()\n> +{\n> +  auto c = [](double x) { return 10; };\n> +  VERIFY(  is_default(std::initializer_list<double>{}, c) );\n> +  VERIFY(  is_default(std::initializer_list<double>{4.2}, c) );\n> +  VERIFY(  is_default(std::initializer_list<double>{0.0, 1.0}, c) );\n> +  VERIFY( !is_default(std::initializer_list<double>{0.0, 0.5}, c) );\n> +  VERIFY( !is_default(std::initializer_list<double>{0.0, 0.5, 1.0}, c) );\n> +\n> +  auto id = [](double x) { return x; };\n>\nThis gives a weight of 0, which breaks the precondition if we have a single\nelement; I changed it to 1.0 + x locally.\n\n> +  VERIFY(  is_default(std::initializer_list<double>{}, id) );\n> +  VERIFY(  is_default(std::initializer_list<double>{4.2}, id) );\n> +  VERIFY(  is_default(std::initializer_list<double>{0.0, 1.0}, id) );\n> +  VERIFY( !is_default(std::initializer_list<double>{0.0, 0.5}, id) );\n> +  VERIFY( !is_default(std::initializer_list<double>{0.0, 0.5, 1.0}, id) );\n> +}\n> +\n> +void test_xbound()\n> +{\n> +  auto c = [](double x) { return 10; };\n> +  VERIFY(  is_default(0, 0.0, 1.0, c) );\n> +  VERIFY( !is_default(0, 0.0, 0.5, c) );\n> +  VERIFY(  is_default(1, 0.0, 1.0, c) );\n> +  VERIFY( !is_default(1, 0.0, 0.5, c) );\n> +  VERIFY( !is_default(2, 0.0, 1.0, c) );\n> +\n> +  auto id = [](double x) { return x; };\n>\nAnd same here.\n\n> +  VERIFY(  is_default(0, 0.0, 1.0, id) );\n> +  VERIFY( !is_default(0, 0.0, 0.5, id) );\n> +  VERIFY(  is_default(1, 0.0, 1.0, id) );\n> +  VERIFY( !is_default(1, 0.0, 0.5, id) );\n> +  VERIFY( !is_default(2, 0.0, 1.0, id) );\n> +}\n> +\n> +int main()\n> +{\n> +  using namespace __gnu_test;\n> +  test_it_pair<input_container>();\n> +  test_it_pair<forward_container>();\n> +  test_it_pair<random_access_container>();\n> +\n> +  test_init_list();\n> +  test_xbound();\n> +  return 0;\n> +}\n> diff --git\n> a/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/cons/range.cc\n> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/cons/range.cc\n> index 3714e460391..4bfa20ea3bb 100644\n> ---\n> a/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/cons/range.cc\n> +++\n> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_constant_distribution/cons/range.cc\n> @@ -25,13 +25,17 @@\n>\n>  #include <random>\n>  #include <testsuite_hooks.h>\n> +#include <testsuite_iterators.h>\n>\n> +template<template<typename> class Range>\n>  void\n> -test01()\n> +test_it_pair()\n>  {\n> -  std::vector<double> x = {0.0, 1.0, 2.0, 3.0, 4.0, 5.0};\n> -  std::vector<double> wt = {0.5, 1.0, 2.5, 1.5, 0.5};\n> -  std::piecewise_constant_distribution<> u(x.begin(), x.end(),\n> wt.begin());\n> +  double x[6] = {0.0, 1.0, 2.0, 3.0, 4.0, 5.0};\n> +  double wt[5] = {0.5, 1.0, 2.5, 1.5, 0.5};\n> +\n> +  Range<double> r(x, x+6);\n> +  std::piecewise_constant_distribution<> u(r.begin(), r.end(), wt);\n>    std::vector<double> interval = u.intervals();\n>    std::vector<double> density = u.densities();\n>    VERIFY( interval.size() == 6 );\n> @@ -44,6 +48,9 @@ test01()\n>\n>  int main()\n>  {\n> -  test01();\n> +  using namespace __gnu_test;\n> +  test_it_pair<input_container>();\n> +  test_it_pair<forward_container>();\n> +  test_it_pair<random_access_container>();\n>    return 0;\n>  }\n> diff --git\n> a/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/cons/fallback.cc\n> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/cons/fallback.cc\n> new file mode 100644\n> index 00000000000..b2e6ca65123\n> --- /dev/null\n> +++\n> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/cons/fallback.cc\n> @@ -0,0 +1,127 @@\n> +// { dg-do run { target c++11 } }\n> +// { dg-require-cstdint \"\" }\n> +\n> +#include <random>\n> +#include <testsuite_hooks.h>\n> +#include <testsuite_iterators.h>\n> +\n> +using dist = std::piecewise_linear_distribution<>;\n> +\n> +template<typename... Args>\n> +bool\n> +is_default(Args&&... args)\n> +{\n> +  std::piecewise_linear_distribution<> u(std::forward<Args>(args)...);\n> +\n> +  std::vector<double> ints = u.intervals();\n> +  if (ints.size() != 2 || ints[0] != 0.0 || ints[1] != 1.0)\n> +    return false;\n> +\n> +  std::vector<double> dens = u.densities();\n> +  if (dens.size() != 2 || dens[0] != 1.0 || dens[1] != 1.0)\n> +    return false;\n> +\n> +  return true;\n> +}\n> +\n> +template<template<typename> class Range>\n> +void\n> +test_it_pair()\n> +{\n> +  double wt[3];\n> +  double x[3];\n> +\n> +  Range<double> r0(x, x);\n> +  VERIFY( is_default(r0.begin(), r0.end(), wt) );\n> +\n> +  x[0] = 4.2;\n> +  Range<double> r1a(x, x+1);\n> +  VERIFY( is_default(r1a.begin(), r1a.end(), wt) );\n> +\n> +  x[0] = 0.0;\n> +  Range<double> r1b(x, x+1);\n> +  VERIFY( is_default(r1b.begin(), r1b.end(), wt) );\n> +\n> +  x[1] = 1.0;\n> +  wt[0] = wt[1] = 13.0;\n> +  Range<double> r2a(x, x+2);\n> +  VERIFY( is_default(r2a.begin(), r2a.end(), wt) );\n> +\n> +  wt[0] = wt[1] = 1.0;\n> +  Range<double> r2b(x, x+2);\n> +  VERIFY( is_default(r2b.begin(), r2b.end(), wt) );\n> +\n> +  wt[1] = 2.0;\n> +  Range<double> r2c(x, x+2);\n> +  VERIFY( !is_default(r2c.begin(), r2c.end(), wt) );\n> +\n> +  x[1] = 0.5;\n> +  wt[0] = wt[1] = 2.0;\n> +  Range<double> r2d(x, x+2);\n> +  VERIFY( !is_default(r2d.begin(), r2d.end(), wt) );\n> +\n> +  x[2] = 1.0;\n> +  wt[2] = wt[0];\n> +  Range<double> r3(x, x+3);\n> +  VERIFY( !is_default(r3.begin(), r3.end(), wt) );\n> +}\n> +\n> +void test_init_list()\n> +{\n> +  auto c1 = [](double x) { return 1.0; };\n> +  VERIFY(  is_default(std::initializer_list<double>{}, c1) );\n> +  VERIFY(  is_default(std::initializer_list<double>{4.2}, c1) );\n> +  VERIFY(  is_default(std::initializer_list<double>{0.0, 1.0}, c1) );\n> +  VERIFY( !is_default(std::initializer_list<double>{0.0, 0.5}, c1) );\n> +  VERIFY( !is_default(std::initializer_list<double>{0.0, 0.5, 1.0}, c1) );\n> +\n> +  auto c2 = [](double x) { return 4.2; };\n> +  VERIFY(  is_default(std::initializer_list<double>{}, c2) );\n> +  VERIFY(  is_default(std::initializer_list<double>{4.2}, c2) );\n> +  VERIFY(  is_default(std::initializer_list<double>{0.0, 1.0}, c2) );\n> +  VERIFY( !is_default(std::initializer_list<double>{0.0, 0.5}, c2) );\n> +  VERIFY( !is_default(std::initializer_list<double>{0.0, 0.5, 1.0}, c2) );\n> +\n> +  auto id = [](double x) { return x; };\n> +  VERIFY(  is_default(std::initializer_list<double>{}, id) );\n> +  VERIFY(  is_default(std::initializer_list<double>{4.2}, id) );\n> +  VERIFY( !is_default(std::initializer_list<double>{0.0, 1.0}, id) );\n> +  VERIFY( !is_default(std::initializer_list<double>{0.0, 0.5}, id) );\n> +  VERIFY( !is_default(std::initializer_list<double>{0.0, 0.5, 1.0}, id) );\n> +}\n> +\n> +void test_xbound()\n> +{\n> +  auto c1 = [](double x) { return 1.0; };\n> +  VERIFY(  is_default(0, 0.0, 1.0, c1) );\n> +  VERIFY( !is_default(0, 0.0, 0.5, c1) );\n> +  VERIFY(  is_default(1, 0.0, 1.0, c1) );\n> +  VERIFY( !is_default(1, 0.0, 0.5, c1) );\n> +  VERIFY( !is_default(2, 0.0, 1.0, c1) );\n> +\n> +  auto c2 = [](double x) { return 4.2; };\n> +  VERIFY(  is_default(0, 0.0, 1.0, c2) );\n> +  VERIFY( !is_default(0, 0.0, 0.5, c2) );\n> +  VERIFY(  is_default(1, 0.0, 1.0, c2) );\n> +  VERIFY( !is_default(1, 0.0, 0.5, c2) );\n> +  VERIFY( !is_default(2, 0.0, 1.0, c2) );\n> +\n> +  auto id = [](double x) { return x; };\n> +  VERIFY( !is_default(0, 0.0, 1.0, id) );\n> +  VERIFY( !is_default(0, 0.0, 0.5, id) );\n> +  VERIFY( !is_default(1, 0.0, 1.0, id) );\n> +  VERIFY( !is_default(1, 0.0, 0.5, id) );\n> +  VERIFY( !is_default(2, 0.0, 1.0, id) );\n> +}\n> +\n> +int main()\n> +{\n> +  using namespace __gnu_test;\n> +  test_it_pair<input_container>();\n> +  test_it_pair<forward_container>();\n> +  test_it_pair<random_access_container>();\n> +\n> +  test_init_list();\n> +  test_xbound();\n> +  return 0;\n> +}\n> diff --git\n> a/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/cons/range.cc\n> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/cons/range.cc\n> index c698e7a66e6..af979fdac42 100644\n> ---\n> a/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/cons/range.cc\n> +++\n> b/libstdc++-v3/testsuite/26_numerics/random/piecewise_linear_distribution/cons/range.cc\n> @@ -25,13 +25,17 @@\n>\n>  #include <random>\n>  #include <testsuite_hooks.h>\n> +#include <testsuite_iterators.h>\n>\n> +template<template<typename> class Range>\n>  void\n> -test01()\n> +test_it_pair()\n>  {\n> -  std::vector<double> x = {0.0, 1.0, 2.0, 3.0, 4.0, 5.0};\n> -  std::vector<double> wt = {0.0, 1.0, 2.5, 1.5, 3.5, 0.0};\n> -  std::piecewise_linear_distribution<> u(x.begin(), x.end(), wt.begin());\n> +  double x[] = {0.0, 1.0, 2.0, 3.0, 4.0, 5.0};\n> +  double wt[] = {0.0, 1.0, 2.5, 1.5, 3.5, 0.0};\n> +\n> +  Range<double> r(x, x+6);\n> +  std::piecewise_linear_distribution<> u(r.begin(), r.end(), wt);\n>    std::vector<double> interval = u.intervals();\n>    std::vector<double> density = u.densities();\n>    VERIFY( interval.size() == 6 );\n> @@ -44,6 +48,9 @@ test01()\n>\n>  int main()\n>  {\n> -  test01();\n> +  using namespace __gnu_test;\n> +  test_it_pair<input_container>();\n> +  test_it_pair<forward_container>();\n> +  test_it_pair<random_access_container>();\n>    return 0;\n>  }\n> --\n> 2.54.0\n>\n>","headers":{"Return-Path":"<gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org>","X-Original-To":["incoming@patchwork.ozlabs.org","gcc-patches@gcc.gnu.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","gcc-patches@gcc.gnu.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=YoPmEyQ3;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; helo=vm01.sourceware.org;\n envelope-from=gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org;\n receiver=patchwork.ozlabs.org)","sourceware.org;\n\tdkim=pass (1024-bit key,\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=YoPmEyQ3","sourceware.org; dmarc=pass (p=quarantine dis=none)\n header.from=redhat.com","sourceware.org; spf=pass smtp.mailfrom=redhat.com","server2.sourceware.org;\n arc=none smtp.remote-ip=170.10.129.124"],"Received":["from vm01.sourceware.org (vm01.sourceware.org\n [IPv6:2620:52:6:3111::32])\n\t(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n\t key-exchange x25519 server-signature ECDSA (secp384r1) server-digest SHA384)\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4g5wdy0BFYz1xqf\n\tfor <incoming@patchwork.ozlabs.org>; Thu, 30 Apr 2026 23:54:42 +1000 (AEST)","from vm01.sourceware.org (localhost [127.0.0.1])\n\tby sourceware.org (Postfix) with ESMTP id 0AFCF436F3D6\n\tfor <incoming@patchwork.ozlabs.org>; Thu, 30 Apr 2026 13:54:40 +0000 (GMT)","from us-smtp-delivery-124.mimecast.com\n (us-smtp-delivery-124.mimecast.com [170.10.129.124])\n by sourceware.org (Postfix) with ESMTP id 4827D43B5531\n for <gcc-patches@gcc.gnu.org>; Thu, 30 Apr 2026 13:54:03 +0000 (GMT)","from mail-yx1-f72.google.com (mail-yx1-f72.google.com\n [74.125.224.72]) by relay.mimecast.com with ESMTP with STARTTLS\n (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id\n us-mta-287-FDQRZ5GbO5WJWaC0rjPgLw-1; Thu, 30 Apr 2026 09:54:01 -0400","by mail-yx1-f72.google.com with SMTP id\n 956f58d0204a3-65c2066bbbeso659000d50.3\n for <gcc-patches@gcc.gnu.org>; Thu, 30 Apr 2026 06:54:00 -0700 (PDT)"],"DKIM-Filter":["OpenDKIM Filter v2.11.0 sourceware.org 0AFCF436F3D6","OpenDKIM Filter v2.11.0 sourceware.org 4827D43B5531"],"DMARC-Filter":"OpenDMARC Filter v1.4.2 sourceware.org 4827D43B5531","ARC-Filter":"OpenARC Filter v1.0.0 sourceware.org 4827D43B5531","ARC-Seal":"i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1777557243; cv=none;\n b=c9YVZOJkSHpF6ujAZv7s5WVP7kqMvM3juw7FqSk9nCTWNlmyFwXc7+pEcMHCAmm0thhdvO5wpyN5UOfSCCORJedHPXbtjxrCxtDeZaTJdxSsp64FmcTUrLN9SETchRFtP1B6vrbB2J4o1cKG7n+TzVXZo3u65CdcExAi2GGc/6s=","ARC-Message-Signature":"i=1; a=rsa-sha256; d=sourceware.org; s=key;\n t=1777557243; c=relaxed/simple;\n bh=ZU8GdygHwmKxjwGBB7R55YJnwK1oeggZS1RYgcggBO4=;\n h=DKIM-Signature:MIME-Version:From:Date:Message-ID:Subject:To;\n b=r1Wmpg4rGG+JIOVJ5Xml/4g4xLerOHAOAH5FAVTRmiE9S+NtoocbUVAhD6rL6sA+5s8uyYpv/5/D3zLrocO9Rf3JfoS+XdaD3LQt6/Jm+rU1Z9U0bW4ehTAQ+wuefoiFv+j/C98QmXD4v+ryrDxvSSn3YLWPi+Y95uIIGDtaUSs=","ARC-Authentication-Results":"i=1; server2.sourceware.org","DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;\n s=mimecast20190719; t=1777557242;\n h=from:from:reply-to:subject:subject:date:date:message-id:message-id:\n to:to:cc:mime-version:mime-version:content-type:content-type:\n in-reply-to:in-reply-to:references:references;\n bh=v6QTvk3dlaQSbE6z5xT4Vvmq0gPdU6M+P3ZpAyShWd8=;\n b=YoPmEyQ3qDoo6rFROxcrAnhRsj/VpFDHiinzpoXikqIcOHhT+q4PtAH5y8VdRAeY5WuYrH\n ZGe3Bi+oSNB2g03I/ZsXLa9LcSe6zeCUlXnPvxxMdeBCbUYytxinaGPDMC53Xi/YmWkSP5\n iZqsOv2zjRv4XL5kkyqFKRTFJNd9wsI=","X-MC-Unique":"FDQRZ5GbO5WJWaC0rjPgLw-1","X-Mimecast-MFC-AGG-ID":"FDQRZ5GbO5WJWaC0rjPgLw_1777557240","X-Google-DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/relaxed;\n d=1e100.net; s=20251104; t=1777557240; x=1778162040;\n h=to:subject:message-id:date:from:in-reply-to:references:mime-version\n :x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id\n :reply-to;\n bh=v6QTvk3dlaQSbE6z5xT4Vvmq0gPdU6M+P3ZpAyShWd8=;\n b=GNHtCoIziRDsDCkAkFvg71h0GLxs6ZdzsaEwcqh+/IVusb/gxHiBJE8XEtZDQD1igy\n /XFq4/xNlFb8axnuZbSELvwhi2cudlOLxGHgk4z0BDBV5sX4Uv/kf4G6pM8F9fg2dP6j\n 9q0+eT48maE/iI3kkbbkzhqAlYJEjPBhLBonuBtXnN35hfzLsJsAjFFA9Lu9JQJ123qo\n +yQIKxyD3jGjIu2uBvvp1I6lEWL204F3rbCkK2A3gITOqYBhl/P74gMJeE5NYglupzty\n 67CyzflJqDB2nMUX0+kQAnEUBuqFO9WywXJml89bx+U8C2CWB+m5WdhsCozAisuiER1B\n hh2w==","X-Forwarded-Encrypted":"i=1;\n AFNElJ/MOkaLeH0I7ouTcaLMGkNLkJ4CALhDhBg8viDgsw/XTzS+5vJOwnJ+1OB1D8xjKsi7YjIcX5yilukn0Q==@gcc.gnu.org","X-Gm-Message-State":"AOJu0YzHQOZY2/jidkofHPA96nE215bParSDVh0pmKdiWCg1YCLzLvNW\n DKy2gt5uRskG21gUCwbCcTAbehPrLdkhCSrVUYVJJwGpwt8P6x2Nupe0R3vbdQvlMj8alYY2r+E\n crJ7FImjcq63iyPFKXLLv2VI0ISAdBx/6m4/Ej7cxAPmVcHPHOjwZektftl2wk1q6nvq29wco3Z\n HGWbKKMLK9NuRaS6gKV/J77k8IU77FhURcc7B6RLt5dQ==","X-Gm-Gg":"AeBDieum7o2Y74W6hfIXPwDTujX/wfpVpFKKWiWGOtd7jthatteeXRixiK/aJIB+xFu\n R84hG8cWLSJ7QR5ZItVT3Wwu/x4P7XtmhAqwgmzxOHbKr6H/Rp3b4t15rwoFXjELYo7MG+1qTJ+\n BBkcYf7Fa2cb+mqUxCUr4Ta7YTb5FR8N7ocPcj2SPsZJayBfrct3kZPwZCQ/OtqboD8ZSuUCpt6\n WjC+GtyrKMAU+qMcsiwzOVIF5jeitQfq2iSpPCYfWGnWCe5Y1FdvSShwRe31uvD2Bh/FyW7boUJ\n hA==","X-Received":["by 2002:a05:690c:9b0a:b0:7bd:4cb2:44ba with SMTP id\n 00721157ae682-7bd52abca8fmr32029227b3.44.1777557240016;\n Thu, 30 Apr 2026 06:54:00 -0700 (PDT)","by 2002:a05:690c:9b0a:b0:7bd:4cb2:44ba with SMTP id\n 00721157ae682-7bd52abca8fmr32028837b3.44.1777557239357; Thu, 30 Apr 2026\n 06:53:59 -0700 (PDT)"],"MIME-Version":"1.0","References":"<20260430110413.546515-1-tkaminsk@redhat.com>","In-Reply-To":"<20260430110413.546515-1-tkaminsk@redhat.com>","From":"Tomasz Kaminski <tkaminsk@redhat.com>","Date":"Thu, 30 Apr 2026 15:53:48 +0200","X-Gm-Features":"AVHnY4LF-rkAkpBfNozzpW1kKDHabOPao5N80pQt_JA0ImJHbkSIIYaWogYPtdc","Message-ID":"\n <CAKvuMXB38DJ8CyYfxf6+CUptjL9z+LBzAOZHDgYNq19k06o_5g@mail.gmail.com>","Subject":"Re: [PATCH] libstdc++: Fix reserve of size_t(-1) elements in\n piecewise_constant_distribution. [PR113761]","To":"libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org","X-Mimecast-Spam-Score":"0","X-Mimecast-MFC-PROC-ID":"IOtFAsIkRZjPpFUEoLV5YiUYPox8XmBbsnedhf9uYJY_1777557240","X-Mimecast-Originator":"redhat.com","Content-Type":"multipart/alternative; boundary=\"000000000000d204cc0650adcb0f\"","X-BeenThere":"gcc-patches@gcc.gnu.org","X-Mailman-Version":"2.1.30","Precedence":"list","List-Id":"Gcc-patches mailing list <gcc-patches.gcc.gnu.org>","List-Unsubscribe":"<https://gcc.gnu.org/mailman/options/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=unsubscribe>","List-Archive":"<https://gcc.gnu.org/pipermail/gcc-patches/>","List-Post":"<mailto:gcc-patches@gcc.gnu.org>","List-Help":"<mailto:gcc-patches-request@gcc.gnu.org?subject=help>","List-Subscribe":"<https://gcc.gnu.org/mailman/listinfo/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=subscribe>","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"}}]