1 files changed, 42 insertions, 0 deletions
diff --git a/ext/sqlite_modern_cpp/sqlite_modern_cpp/utility/utf16_utf8.h b/ext/sqlite_modern_cpp/sqlite_modern_cpp/utility/utf16_utf8.h
new file mode 100644
index 0000000..ea21723
--- /dev/null
+++ b/ext/sqlite_modern_cpp/sqlite_modern_cpp/utility/utf16_utf8.h
@@ -0,0 +1,42 @@
+#pragma once
+
+#include <locale>
+#include <string>
+#include <algorithm>
+
+#include "../errors.h"
+
+namespace sqlite {
+	namespace utility {
+		inline std::string utf16_to_utf8(const std::u16string &input) {
+			struct : std::codecvt<char16_t, char, std::mbstate_t> {
+			} codecvt;
+			std::mbstate_t state{};
+			std::string result((std::max)(input.size() * 3 / 2, std::size_t(4)), '\0');
+			const char16_t *remaining_input = input.data();
+			std::size_t produced_output = 0;
+			while(true) {
+				char *used_output;
+				switch(codecvt.out(state, remaining_input, &input[input.size()],
+				                   remaining_input, &result[produced_output],
+				                   &result[result.size() - 1] + 1, used_output)) {
+				case std::codecvt_base::ok:
+					result.resize(used_output - result.data());
+					return result;
+				case std::codecvt_base::noconv:
+					// This should be unreachable
+				case std::codecvt_base::error:
+					throw errors::invalid_utf16("Invalid UTF-16 input", "");
+				case std::codecvt_base::partial:
+					if(used_output == result.data() + produced_output)
+						throw errors::invalid_utf16("Unexpected end of input", "");
+					produced_output = used_output - result.data();
+					result.resize(
+							result.size()
+							+ (std::max)((&input[input.size()] - remaining_input) * 3 / 2,
+							           std::ptrdiff_t(4)));
+				}
+			}
+		}
+	} // namespace utility
+} // namespace sqlite