Create to_string.hpp

diff --git a/to_string.hpp b/to_string.hpp
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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>
+
+/**
+ * @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 16 (though no checking is done)
+ */
+template<auto N, unsigned int base = 10, std::enable_if_t<std::is_integral_v<decltype(N)>, int> = 0>
+struct to_string_t {
+    // The lambda calculates what the string length of N will be, so that `buf`
+    // fits to the number perfectly.
+    char buf[([] {
+                  unsigned int len = N >= 0 ? 1 : 2;
+                  for (auto n = N < 0 ? -N : N; n; len++, n /= base);
+                  return len;
+             }())];
+
+    /**
+     * Constructs the object, filling `buf` with the string representation of N.
+     */
+    constexpr to_string_t() {
+        unsigned int len = N >= 0 ? 1 : 2;
+        for (auto n = N < 0 ? -N : N; n; len++, n /= base);
+
+        auto ptr = buf + len;
+        *--ptr = '\0';
+        for (auto n = N < 0 ? -N : N; n; n /= base)
+            *--ptr = "0123456789ABCDEF"[n % base];
+        if (N < 0)
+            *--ptr = '-';
+    }
+
+    /**
+     * Allows implicit conversion of this object to a `char *`.
+     */
+    constexpr operator char *() {
+        return buf;
+    }
+    
+    /**
+     * Allows implicit conversion of this object to a `const char *`.
+     */
+    constexpr operator const char *() const {
+        return buf;
+    }
+};
+
+/**
+ * Simplifies use of `to_string_t` from `to_string_t<N>()` to `to_string<N>`.
+ */
+template<auto N, unsigned int base = 10>
+to_string_t<N, base> to_string;
+ 
+#endif // TCSULLIVAN_TO_STRING_HPP_