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Added bit_cast 
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-73
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3 files changed

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-73
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‎include/sfl/detail/bit/bit_cast.hpp‎

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//
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// Copyright (c) 2022 Slaven Falandys
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//
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// This software is provided 'as-is', without any express or implied
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// warranty. In no event will the authors be held liable for any damages
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// arising from the use of this software.
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//
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// Permission is granted to anyone to use this software for any purpose,
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// including commercial applications, and to alter it and redistribute it
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// freely, subject to the following restrictions:
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//
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// 1. The origin of this software must not be misrepresented; you must not
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// claim that you wrote the original software. If you use this software
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// in a product, an acknowledgment in the product documentation would be
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// appreciated but is not required.
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// 2. Altered source versions must be plainly marked as such, and must not be
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// misrepresented as being the original software.
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// 3. This notice may not be removed or altered from any source distribution.
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//
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#ifndef SFL_DETAIL_BIT_CAST_HPP_INCLUDED
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#define SFL_DETAIL_BIT_CAST_HPP_INCLUDED
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#include <sfl/detail/cpp.hpp>
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#include <cstring> // memcpy
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#include <type_traits> // is_trivially_copyable
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#if SFL_CPP_VERSION >= SFL_CPP_20
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#include <bit> // bit_cast
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#endif
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namespace sfl
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{
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namespace dtl
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{
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///////////////////////////////////////////////////////////////////////////////
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///////////////////////////////////////////////////////////////////////////////
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// C++11 implementation
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///////////////////////////////////////////////////////////////////////////////
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///////////////////////////////////////////////////////////////////////////////
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template <class To, class From>
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To bit_cast_impl_11(const From& src) noexcept
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{
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static_assert(sizeof(To) == sizeof(From), "Size mismatch");
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static_assert(std::is_trivially_copyable<From>::value, "From must be trivially copyable");
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static_assert(std::is_trivially_copyable<To>::value, "To must be trivially copyable");
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To dst;
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std::memcpy(&dst, &src, sizeof(To));
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return dst;
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}
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///////////////////////////////////////////////////////////////////////////////
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///////////////////////////////////////////////////////////////////////////////
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// C++20 implementation
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///////////////////////////////////////////////////////////////////////////////
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///////////////////////////////////////////////////////////////////////////////
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#if SFL_CPP_VERSION >= SFL_CPP_20
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template <class To, class From>
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constexpr To bit_cast_impl_20(const From& from) noexcept
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{
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return std::bit_cast<To>(from);
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}
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#endif // SFL_CPP_VERSION >= SFL_CPP_20
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///////////////////////////////////////////////////////////////////////////////
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///////////////////////////////////////////////////////////////////////////////
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// BIT CAST
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///////////////////////////////////////////////////////////////////////////////
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///////////////////////////////////////////////////////////////////////////////
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template <class To, class From>
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SFL_CONSTEXPR_20
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To bit_cast(const From& from) noexcept
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{
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#if SFL_CPP_VERSION >= SFL_CPP_20
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return sfl::dtl::bit_cast_impl_20<To>(from);
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#else
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return sfl::dtl::bit_cast_impl_11<To>(from);
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#endif
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}
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} // namespace dtl
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} // namespace sfl
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#endif // SFL_DETAIL_BIT_CAST_HPP_INCLUDED

‎include/sfl/hash.hpp‎

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@@ -21,6 +21,7 @@
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#ifndef SFL_HASH_HPP_INCLUDED
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#define SFL_HASH_HPP_INCLUDED
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#include <sfl/detail/bit/bit_cast.hpp>
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#include <sfl/detail/type_traits/enable_if_t.hpp>
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#include <sfl/detail/cpp.hpp>
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@@ -30,10 +31,6 @@
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#include <limits> // numeric_limits
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#include <type_traits> // is_enum, is_integral, is_floating_point
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33-
#if SFL_CPP_VERSION >= SFL_CPP_20
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#include <bit> // bit_cast
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#endif
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namespace sfl
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{
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@@ -84,22 +81,7 @@ struct hash_impl<T, sfl::dtl::enable_if_t<std::is_floating_point<T>::value && si
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value = std::numeric_limits<T>::quiet_NaN();
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}
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87-
#if SFL_CPP_VERSION >= SFL_CPP_20
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if (std::is_constant_evaluated())
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{
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return std::bit_cast<std::uint32_t>(value);
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}
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else
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#endif
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{
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union
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{
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T t;
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std::uint32_t a;
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} u;
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u.t = value;
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return u.a;
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}
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return sfl::dtl::bit_cast<std::uint32_t>(value);
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}
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};
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@@ -121,22 +103,7 @@ struct hash_impl<T, sfl::dtl::enable_if_t<std::is_floating_point<T>::value && si
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value = std::numeric_limits<T>::quiet_NaN();
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}
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124-
#if SFL_CPP_VERSION >= SFL_CPP_20
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if (std::is_constant_evaluated())
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{
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return std::bit_cast<std::uint32_t>(value);
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}
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else
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#endif
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{
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union
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{
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T t;
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std::uint32_t a;
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} u;
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u.t = value;
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return u.a;
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}
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return sfl::dtl::bit_cast<std::uint32_t>(value);
140107
}
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};
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@@ -158,27 +125,10 @@ struct hash_impl<T, sfl::dtl::enable_if_t<std::is_floating_point<T>::value && si
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value = std::numeric_limits<T>::quiet_NaN();
159126
}
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161-
#if SFL_CPP_VERSION >= SFL_CPP_20
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if (std::is_constant_evaluated())
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{
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std::uint64_t bits = std::bit_cast<std::uint64_t>(value);
165-
std::size_t h1 = static_cast<std::size_t>(bits);
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std::size_t h2 = static_cast<std::size_t>(bits >> 32);
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return h1 ^ (h2 + 0x9e3779b9u + (h1 << 6) + (h1 >> 2));
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}
169-
else
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#endif
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{
172-
union
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{
174-
T t;
175-
std::uint64_t a;
176-
} u;
177-
u.t = value;
178-
std::size_t h1 = static_cast<std::size_t>(u.a);
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std::size_t h2 = static_cast<std::size_t>(u.a >> 32);
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return h1 ^ (h2 + 0x9e3779b9u + (h1 << 6) + (h1 >> 2));
181-
}
128+
std::uint64_t bits = sfl::dtl::bit_cast<std::uint64_t>(value);
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std::size_t h1 = static_cast<std::size_t>(bits);
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std::size_t h2 = static_cast<std::size_t>(bits >> 32);
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return h1 ^ (h2 + 0x9e3779b9u + (h1 << 6) + (h1 >> 2));
182132
}
183133
};
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@@ -200,22 +150,7 @@ struct hash_impl<T, sfl::dtl::enable_if_t<std::is_floating_point<T>::value && si
200150
value = std::numeric_limits<T>::quiet_NaN();
201151
}
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203-
#if SFL_CPP_VERSION >= SFL_CPP_20
204-
if (std::is_constant_evaluated())
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{
206-
return std::bit_cast<std::uint64_t>(value);
207-
}
208-
else
209-
#endif
210-
{
211-
union
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{
213-
T t;
214-
std::uint64_t a;
215-
} u;
216-
u.t = value;
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return u.a;
218-
}
153+
return sfl::dtl::bit_cast<std::uint64_t>(value);
219154
}
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};
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‎test/src/bit/bit_cast.cpp‎

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#undef NDEBUG // This is very important. Must be in the first line.
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#include "sfl/detail/bit/bit_cast.hpp"
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#include <cstdint>
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#include <cstdlib>
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#include <iostream>
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#include <limits>
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#include <random>
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#include <type_traits>
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#if SFL_CPP_VERSION >= SFL_CPP_20
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template <typename T>
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void test(std::size_t n)
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{
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using unsigned_t = std::conditional_t
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<
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sizeof(T) == 4,
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std::uint32_t,
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std::conditional_t
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<
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sizeof(T) == 8,
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std::uint64_t,
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std::false_type
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>
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>;
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static_assert(!std::is_same_v<unsigned_t, std::false_type>);
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std::random_device rd;
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std::mt19937 gen(rd());
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std::uniform_int_distribution<unsigned_t> dist
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(
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std::numeric_limits<unsigned_t>::min(),
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std::numeric_limits<unsigned_t>::max()
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);
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for (std::size_t i = 0; i < 10; ++i)
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{
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for (std::size_t j = 0; j < (n / 10); ++j)
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{
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const T value = static_cast<T>(dist(gen));
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const unsigned_t h_11 = sfl::dtl::bit_cast_impl_11<unsigned_t>(value);
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const unsigned_t h_20 = sfl::dtl::bit_cast_impl_20<unsigned_t>(value);
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if (h_11 != h_20)
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{
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std::cout << "ERROR: Hash mismatch\n"
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<< " - value: " << value << "\n"
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<< " - h_11: " << h_11 << "\n"
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<< " - h_20: " << h_20 << std::endl;
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std::abort();
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}
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}
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std::cout << " " << ((i + 1) * 10) << "%" << std::endl;
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}
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}
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int main()
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{
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constexpr std::size_t n = 1'000'000;
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std::cout << "Testing with `int`..." << std::endl;
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test<int>(n);
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std::cout << "Testing with `long`..." << std::endl;
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test<long>(n);
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std::cout << "Testing with `long long`..." << std::endl;
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test<long long>(n);
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std::cout << "Testing with `float`..." << std::endl;
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test<float>(n);
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std::cout << "Testing with `double`..." << std::endl;
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test<double>(n);
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}
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#else // before C++20
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int main()
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{
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// Nothing to do
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}
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#endif // before C++20

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