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75 lines
2.7 KiB
C++
75 lines
2.7 KiB
C++
/**
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* to_string.hpp - Provides compile-time integer-to-string conversion.
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* Written by Clyne Sullivan.
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* https://github.com/tcsullivan/constexpr-to-string
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*/
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#ifndef TCSULLIVAN_TO_STRING_HPP_
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#define TCSULLIVAN_TO_STRING_HPP_
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#include <type_traits>
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/**
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* @struct to_string_t
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* @brief Provides the ability to convert any integral to a string at compile-time.
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* @tparam N Number to convert
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* @tparam base Desired base, can be from 2 to 36
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*/
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template<auto N, int base, typename char_type,
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std::enable_if_t<std::is_integral_v<decltype(N)>, int> = 0,
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std::enable_if_t<(base > 1 && base < 37), int> = 0>
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class to_string_t {
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// The lambda calculates what the string length of N will be, so that `buf`
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// fits to the number perfectly.
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char_type buf[([]() constexpr noexcept {
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unsigned int len = N > 0 ? 1 : 2;
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for (auto n = N; n; len++, n /= base);
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return len;
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}())] = {};
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public:
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/**
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* Constructs the object, filling `buf` with the string representation of N.
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*/
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constexpr to_string_t() noexcept {
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auto ptr = end();
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*--ptr = '\0';
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if (N != 0) {
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for (auto n = N; n; n /= base)
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*--ptr = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"[(N < 0 ? -1 : 1) * (n % base)];
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if (N < 0)
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*--ptr = '-';
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} else {
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buf[0] = '0';
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}
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}
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// Support implicit casting to `char *` or `const char *`.
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constexpr operator char_type *() noexcept { return buf; }
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constexpr operator const char_type *() const noexcept { return buf; }
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constexpr auto size() const noexcept { return sizeof(buf) / sizeof(buf[0]); }
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// Element access
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constexpr auto data() noexcept { return buf; }
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constexpr const auto data() const noexcept { return buf; }
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constexpr auto& operator[](unsigned int i) noexcept { return buf[i]; }
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constexpr const auto& operator[](unsigned int i) const noexcept { return buf[i]; }
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constexpr auto& front() noexcept { return buf[0]; }
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constexpr const auto& front() const noexcept { return buf[0]; }
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constexpr auto& back() noexcept { return buf[size() - 1]; }
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constexpr const auto& back() const noexcept { return buf[size() - 1]; }
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// Iterators
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constexpr auto begin() noexcept { return buf; }
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constexpr const auto begin() const noexcept { return buf; }
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constexpr auto end() noexcept { return buf + size(); }
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constexpr const auto end() const noexcept { return buf + size(); }
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};
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/**
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* Simplifies use of `to_string_t` from `to_string_t<N>()` to `to_string<N>`.
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*/
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template<auto N, int base = 10, typename char_type = char>
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constexpr to_string_t<N, base, char_type> to_string;
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#endif // TCSULLIVAN_TO_STRING_HPP_
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