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