cast.hpp

// Copyright Take Vos 2020-2022.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
 
#include "utility.hpp"
#include "type_traits.hpp"
#include "concepts.hpp"
#include "assert.hpp"
#include "compare.hpp"
#include <type_traits>
#include <concepts>
#include <climits>
#include <span>
 
hi_warning_push();
// C26472: Don't use static_cast for arithmetic conversions, Use brace initialization, gsl::narrow_cast or gsl::narrow (type.1).
// This file implements narrow_cast().
hi_warning_ignore_msvc(26472);
// C26467: Converting from floating point to unsigned integral types results in non-portable code if the double/float has
// a negative value. Use gsl::narrow_cast or gsl::naroow instead to guard against undefined behavior and potential data loss
// (es.46).
// This file implements narrow_cast().
hi_warning_ignore_msvc(26467);
// C26496: The variable 'r' does not change after construction, mark it as const (con.4).
// False positive
hi_warning_ignore_msvc(26496);
// C26466: Don't use static_cast downcast. A cast from a polymorphic type should use dynamic_cast (type.2)
// Used in down_cast<>() specifically for doing this savely.
hi_warning_ignore_msvc(26466);
// C26474: Don't cast between pointer types when the conversion could be implicit (type.1).
// Since these functions are templates this happens.
hi_warning_ignore_msvc(26474);
 
namespace hi::inline v1 {
template<typename T>
[[nodiscard]] constexpr T copy(T value) noexcept
{
    return value;
}
 
template<typename Out, std::derived_from<std::remove_pointer_t<Out>> In>
[[nodiscard]] constexpr Out up_cast(In *rhs) noexcept
    requires std::is_pointer_v<Out> and
    (std::is_const_v<std::remove_pointer_t<Out>> == std::is_const_v<In> or std::is_const_v<std::remove_pointer_t<Out>>)
{
    if constexpr (std::is_same_v<std::remove_const_t<In>, remove_cvptr_t<Out>>) {
        return rhs;
    } else {
        return static_cast<Out>(rhs);
    }
}
 
template<typename Out>
[[nodiscard]] constexpr Out up_cast(nullptr_t) noexcept
    requires std::is_pointer_v<Out>
{
    return nullptr;
}
 
template<typename Out, std::derived_from<std::remove_reference_t<Out>> In>
[[nodiscard]] constexpr Out up_cast(In& rhs) noexcept
    requires std::is_reference_v<Out> and
    (std::is_const_v<std::remove_reference_t<Out>> == std::is_const_v<In> or std::is_const_v<std::remove_reference_t<Out>>)
{
    if constexpr (std::is_same_v<std::remove_const_t<In>, std::remove_cvref_t<Out>>) {
        return rhs;
    } else {
        return static_cast<Out>(rhs);
    }
}
 
template<typename Out, base_of<std::remove_pointer_t<Out>> In>
[[nodiscard]] constexpr Out down_cast(In *rhs) noexcept
    requires std::is_pointer_v<Out> and
    (std::is_const_v<std::remove_pointer_t<Out>> == std::is_const_v<In> or std::is_const_v<std::remove_pointer_t<Out>>)
{
    if constexpr (std::is_same_v<std::remove_const_t<In>, remove_cvptr_t<Out>>) {
        return rhs;
    } else {
        hi_axiom(rhs == nullptr or dynamic_cast<Out>(rhs) != nullptr);
        return static_cast<Out>(rhs);
    }
}
 
template<typename Out>
[[nodiscard]] constexpr Out down_cast(nullptr_t) noexcept
    requires std::is_pointer_v<Out>
{
    return nullptr;
}
 
template<typename Out, base_of<std::remove_reference_t<Out>> In>
[[nodiscard]] constexpr Out down_cast(In& rhs) noexcept
    requires std::is_reference_v<Out> and
    (std::is_const_v<std::remove_reference_t<Out>> == std::is_const_v<In> or std::is_const_v<std::remove_reference_t<Out>>)
{
    if constexpr (std::is_same_v<std::remove_const_t<In>, std::remove_cvref_t<Out>>) {
        return rhs;
    } else {
        hi_axiom(dynamic_cast<std::add_pointer_t<std::remove_reference_t<Out>>>(std::addressof(rhs)) != nullptr);
        return static_cast<Out>(rhs);
    }
}
 
template<arithmetic Out, arithmetic In>
[[nodiscard]] constexpr Out wide_cast(In rhs) noexcept
    requires(type_in_range_v<Out, In>)
{
    return static_cast<Out>(rhs);
}
 
template<arithmetic Out>
[[nodiscard]] constexpr Out wide_cast(bool rhs) noexcept
{
    return static_cast<Out>(rhs);
}
 
namespace detail {
 
template<arithmetic Out, arithmetic In>
[[nodiscard]] constexpr bool narrow_validate(Out out, In in) noexcept
{
    // in- and out-value compares the same, after converting out-value back to in-type.
    auto r = (in == static_cast<In>(out));
 
    // If the types have different signs we need to do an extra test to make sure the actual sign
    // of the values are the same as well.
    if constexpr (std::numeric_limits<Out>::is_signed != std::numeric_limits<In>::is_signed) {
        r &= (in < In{}) == (out < Out{});
    }
 
    return r;
}
 
} // namespace detail
 
template<std::integral Out, arithmetic In>
[[nodiscard]] constexpr Out saturate_cast(In rhs) noexcept
{
    if constexpr (std::is_floating_point_v<In>) {
        if (std::isnan(rhs)) {
            return Out{0};
        }
    }
 
    if (three_way_compare(rhs, std::numeric_limits<Out>::lowest()) != std::strong_ordering::greater) {
        return std::numeric_limits<Out>::lowest();
    } else if (three_way_compare(rhs, std::numeric_limits<Out>::max()) != std::strong_ordering::less) {
        return std::numeric_limits<Out>::max();
    } else {
        return static_cast<Out>(rhs);
    }
}
 
template<typename Out, typename In>
[[nodiscard]] constexpr Out narrow_cast(In const& rhs) noexcept;
 
template<arithmetic Out, arithmetic In>
[[nodiscard]] constexpr Out narrow_cast(In const& rhs) noexcept
{
    if constexpr (type_in_range_v<Out, In>) {
        return static_cast<Out>(rhs);
    } else {
        hilet r = static_cast<Out>(rhs);
        hi_axiom(detail::narrow_validate(r, rhs));
        return r;
    }
}
 
template<arithmetic Out, arithmetic In>
[[nodiscard]] constexpr Out round_cast(In rhs) noexcept
{
    if constexpr (std::is_floating_point_v<In>) {
        return narrow_cast<Out>(std::round(rhs));
    } else {
        return narrow_cast<Out>(rhs);
    }
}
 
template<arithmetic Out, arithmetic In>
[[nodiscard]] constexpr Out floor_cast(In rhs) noexcept
{
    if constexpr (std::is_floating_point_v<In>) {
        return narrow_cast<Out>(std::floor(rhs));
    } else {
        return narrow_cast<Out>(rhs);
    }
}
 
template<arithmetic Out, arithmetic In>
[[nodiscard]] constexpr Out ceil_cast(In rhs) noexcept
{
    if constexpr (std::is_floating_point_v<In>) {
        return narrow_cast<Out>(std::ceil(rhs));
    } else {
        return narrow_cast<Out>(rhs);
    }
}
 
template<std::integral In>
[[nodiscard]] constexpr std::make_unsigned_t<In> to_unsigned(In rhs) noexcept
{
    return static_cast<std::make_unsigned_t<In>>(rhs);
}
 
template<std::integral In>
[[nodiscard]] constexpr std::make_signed_t<In> to_signed(In rhs) noexcept
{
    return static_cast<std::make_signed_t<In>>(rhs);
}
 
template<std::integral Out, std::integral In>
[[nodiscard]] constexpr Out truncate(In rhs) noexcept
{
    return static_cast<Out>(to_unsigned(rhs));
}
 
template<std::integral Out, std::integral In>
[[nodiscard]] constexpr Out char_cast(In rhs) noexcept
{
    using in_unsigned_type = std::make_unsigned_t<In>;
    using out_unsigned_type = std::make_unsigned_t<Out>;
 
    // We cast to unsigned of the same type, so that we don't accidentally sign extent 'char'.
    auto in_unsigned = static_cast<in_unsigned_type>(rhs);
    auto out_unsigned = narrow_cast<out_unsigned_type>(in_unsigned);
    return static_cast<Out>(out_unsigned);
}
 
template<std::integral Out>
[[nodiscard]] constexpr Out char_cast(std::byte rhs) noexcept
{
    return char_cast<Out>(static_cast<uint8_t>(rhs));
}
 
template<std::unsigned_integral OutType, std::unsigned_integral InType>
[[nodiscard]] constexpr OutType low_bit_cast(InType value) noexcept
{
    static_assert(sizeof(OutType) * 2 == sizeof(InType), "Return value of low_bit_cast must be half the size of the input");
    return static_cast<OutType>(value);
}
 
template<std::unsigned_integral OutType, std::unsigned_integral InType>
[[nodiscard]] constexpr OutType high_bit_cast(InType value) noexcept
{
    static_assert(sizeof(OutType) * 2 == sizeof(InType), "Return value of high_bit_cast must be half the size of the input");
    return static_cast<OutType>(value >> sizeof(OutType) * CHAR_BIT);
}
 
template<std::signed_integral OutType, std::signed_integral InType>
[[nodiscard]] constexpr OutType low_bit_cast(InType value) noexcept
{
    using UInType = std::make_unsigned_t<InType>;
    using UOutType = std::make_unsigned_t<OutType>;
    return static_cast<OutType>(low_bit_cast<UOutType>(static_cast<UInType>(value)));
}
 
template<std::signed_integral OutType, std::signed_integral InType>
[[nodiscard]] constexpr OutType high_bit_cast(InType value) noexcept
{
    using UInType = std::make_unsigned_t<InType>;
    using UOutType = std::make_unsigned_t<OutType>;
    return static_cast<OutType>(high_bit_cast<UOutType>(static_cast<UInType>(value)));
}
 
template<std::unsigned_integral OutType, std::signed_integral InType>
[[nodiscard]] constexpr OutType low_bit_cast(InType value) noexcept
{
    using UInType = std::make_unsigned_t<InType>;
    return low_bit_cast<OutType>(static_cast<UInType>(value));
}
 
template<std::unsigned_integral OutType, std::signed_integral InType>
[[nodiscard]] constexpr OutType high_bit_cast(InType value) noexcept
{
    using UInType = std::make_unsigned_t<InType>;
    return high_bit_cast<OutType>(static_cast<UInType>(value));
}
 
template<std::unsigned_integral OutType, std::unsigned_integral InType>
[[nodiscard]] constexpr OutType merge_bit_cast(InType hi, InType lo) noexcept
{
    static_assert(sizeof(OutType) == sizeof(InType) * 2, "Return value of merge_bit_cast must be double the size of the input");
 
    OutType r = static_cast<OutType>(hi);
    r <<= sizeof(InType) * CHAR_BIT;
    r |= static_cast<OutType>(lo);
    return r;
}
 
template<std::signed_integral OutType, std::signed_integral InType>
[[nodiscard]] constexpr OutType merge_bit_cast(InType hi, InType lo) noexcept
{
    using UInType = std::make_unsigned_t<InType>;
    using UOutType = std::make_unsigned_t<OutType>;
    return static_cast<OutType>(merge_bit_cast<UOutType>(static_cast<UInType>(hi), static_cast<UInType>(lo)));
}
 
template<std::signed_integral OutType, std::unsigned_integral InType>
[[nodiscard]] constexpr OutType merge_bit_cast(InType hi, InType lo) noexcept
{
    using UOutType = std::make_unsigned_t<OutType>;
    return narrow_cast<OutType>(merge_bit_cast<UOutType>(hi, lo));
}
 
[[nodiscard]] constexpr auto to_underlying(scoped_enum auto rhs) noexcept
{
    return static_cast<std::underlying_type_t<decltype(rhs)>>(rhs);
}
 
template<typename T>
[[nodiscard]] constexpr bool to_bool(T&& rhs) noexcept
    requires(requires(T&& x) { static_cast<bool>(std::forward<T>(x)); })
{
    return static_cast<bool>(std::forward<T>(rhs));
}
 
template<typename T>
[[nodiscard]] inline T to_ptr(std::intptr_t value) noexcept
    requires std::is_pointer_v<T>
{
    return reinterpret_cast<T>(value);
}
 
template<typename T>
[[nodiscard]] std::intptr_t to_int(T *ptr) noexcept
{
    return reinterpret_cast<std::intptr_t>(ptr);
}
 
template<typename T, byte_like Byte>
[[nodiscard]] copy_cv_t<T, Byte>& implicit_cast(std::span<Byte> bytes)
{
    using value_type = copy_cv_t<T, Byte>;
 
    static_assert(std::is_trivially_default_constructible_v<value_type>);
    static_assert(std::is_trivially_destructible_v<value_type>);
 
    if (sizeof(value_type) > bytes.size()) {
        throw std::bad_cast();
    }
    hi_axiom_not_null(bytes.data());
 
    if constexpr (alignof(value_type) != 1) {
        if (std::bit_cast<std::uintptr_t>(bytes.data()) % alignof(value_type) != 0) {
            throw std::bad_cast();
        }
    }
 
    return *reinterpret_cast<value_type *>(bytes.data());
}
 
template<typename T, byte_like Byte>
[[nodiscard]] std::span<copy_cv_t<T, Byte>> implicit_cast(std::span<Byte> bytes, size_t n)
{
    using value_type = copy_cv_t<T, Byte>;
 
    static_assert(std::is_trivially_default_constructible_v<value_type>);
    static_assert(std::is_trivially_destructible_v<value_type>);
 
    if (sizeof(value_type) * n > bytes.size()) {
        throw std::bad_cast();
    }
    hi_axiom_not_null(bytes.data());
 
    if constexpr (alignof(value_type) != 1) {
        if (std::bit_cast<std::uintptr_t>(bytes.data()) % alignof(value_type) != 0) {
            throw std::bad_cast();
        }
    }
 
    return {reinterpret_cast<value_type *>(bytes.data()), n};
}
 
template<typename T, byte_like Byte>
[[nodiscard]] copy_cv_t<T, Byte>& implicit_cast(size_t& offset, std::span<Byte> bytes)
{
    using value_type = copy_cv_t<T, Byte>;
 
    static_assert(std::is_trivially_default_constructible_v<value_type>);
    static_assert(std::is_trivially_destructible_v<value_type>);
 
    if (sizeof(value_type) + offset > bytes.size()) {
        throw std::bad_cast();
    }
    hi_axiom_not_null(bytes.data());
 
    hilet data = bytes.data() + offset;
 
    if constexpr (alignof(value_type) != 1) {
        if (std::bit_cast<std::uintptr_t>(data) % alignof(value_type) != 0) {
            throw std::bad_cast();
        }
    }
 
    offset += sizeof(value_type);
    return *reinterpret_cast<value_type *>(data);
}
 
template<typename T, byte_like Byte>
[[nodiscard]] std::span<copy_cv_t<T, Byte>> implicit_cast(size_t& offset, std::span<Byte> bytes, size_t n)
{
    using value_type = copy_cv_t<T, Byte>;
 
    static_assert(std::is_trivially_default_constructible_v<value_type>);
    static_assert(std::is_trivially_destructible_v<value_type>);
 
    if (sizeof(value_type) * n + offset > bytes.size()) {
        throw std::bad_cast();
    }
    hi_axiom_not_null(bytes.data());
 
    hilet data = bytes.data() + offset;
 
    if constexpr (alignof(value_type) != 1) {
        if (std::bit_cast<std::uintptr_t>(data) % alignof(value_type) != 0) {
            throw std::bad_cast();
        }
    }
 
    offset += sizeof(value_type) * n;
    return {reinterpret_cast<value_type *>(data), n};
}
 
} // namespace hi::inline v1
 
hi_warning_pop();