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94 lines
3.2 KiB
C++
94 lines
3.2 KiB
C++
/**
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* f_to_string.hpp - Provides compile-time floating-point-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_F_TO_STRING_HPP_
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#define TCSULLIVAN_F_TO_STRING_HPP_
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namespace constexpr_to_string {
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struct double_wrapper {
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long long int whole = 0;
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long long int frac = 0;
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constexpr double_wrapper(double v, int prec = 5) {
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whole = static_cast<long long int>(v);
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v -= whole;
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for (int i = 0; i < prec; i++)
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v *= 10;
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frac = static_cast<long long int>(v);
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}
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};
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/**
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* @struct f_to_string_t
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* @brief Provides the ability to convert a floating-point number to a string at compile-time.
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* @tparam N Number to convert
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*/
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template<double_wrapper N, typename char_type>
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class f_to_string_t {
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char_type buf[([]() constexpr noexcept {
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unsigned int len = 2;
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if (N.whole <= 0) len++;
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for (auto n = N.whole; n; len++, n /= 10);
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if (N.frac == 0 || (N.whole == 0 && N.frac < 0)) len++;
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for (auto n = N.frac; n; len++, n /= 10);
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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 f_to_string_t() noexcept {
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auto append = [](auto V, auto& ptr) {
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if (V != 0) {
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for (auto n = V; n; n /= 10)
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*--ptr = (V < 0 ? -1 : 1) * (n % 10) + '0';
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} else {
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*--ptr = '0';
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}
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};
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auto ptr = end();
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*--ptr = '\0';
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append(N.frac, ptr);
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*--ptr = '.';
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append(N.whole, ptr);
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if (N.frac < 0 || N.whole < 0)
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*--ptr = '-';
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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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} // namespace constexpr_to_string
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/**
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* Simplifies use of `f_to_string_t` from `f_to_string_t<N>()` to `f_to_string<N>`.
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*/
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template<constexpr_to_string::double_wrapper N, typename char_type = char>
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constexpr constexpr_to_string::f_to_string_t<N, char_type> f_to_string;
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#endif // TCSULLIVAN_F_TO_STRING_HPP_
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