Add function to find a UTF-16 position in a UTF-8 string.

1 files changed, 12 insertions, 0 deletions

diff --git a/src/UniConversion.cxx b/src/UniConversion.cxx
index 1287aa612..3b7472638 100644
--- a/src/UniConversion.cxx
+++ b/src/UniConversion.cxx
@@ -37,6 +37,18 @@ size_t UTF8Length(std::wstring_view wsv) {
 	return len;
 }
 
+size_t UTF8PositionFromUTF16Position(std::string_view u8Text, size_t positionUTF16) noexcept {
+	size_t positionUTF8 = 0;
+	for (size_t lengthUTF16 = 0; (positionUTF8 < u8Text.length()) && (lengthUTF16 < positionUTF16);) {
+		const unsigned char uch = u8Text[positionUTF8];
+		const unsigned int byteCount = UTF8BytesOfLead[uch];
+		lengthUTF16 += UTF16LengthFromUTF8ByteCount(byteCount);
+		positionUTF8 += byteCount;
+	}
+
+	return positionUTF8;
+}
+
 void UTF8FromUTF16(std::wstring_view wsv, char *putf, size_t len) {
 	size_t k = 0;
 	for (size_t i = 0; i < wsv.length() && wsv[i];) {