1 files changed, 21 insertions, 0 deletions
diff --git a/src/DBCS.h b/src/DBCS.h
index 01830c843..12bbaf986 100644
--- a/src/DBCS.h
+++ b/src/DBCS.h
@@ -25,8 +25,29 @@ constexpr bool IsDBCSCodePage(int codePage) noexcept {
 }
 
 bool DBCSIsLeadByte(int codePage, char ch) noexcept;
+bool DBCSIsTrailByte(int codePage, char ch) noexcept;
 bool IsDBCSValidSingleByte(int codePage, int ch) noexcept;
 
+// Calculate a number from a DBCS byte pair that can be used to index into an array or map. 
+// Should only be called with genuine DBCS character pairs which means that ch1 has top bit set.
+constexpr uint16_t DBCSIndex(char ch1, char ch2) noexcept {
+	constexpr unsigned int highStart = 0x80U;
+	constexpr unsigned int byteMultiply = 0x100U;
+	const unsigned char uch1 = ch1;
+	const unsigned char uch2 = ch2;
+	return ((uch1 - highStart) * byteMultiply) + uch2;
+}
+
+struct DBCSPair {
+	char chars[2];
+};
+using FoldMap = std::array<DBCSPair, 0x8000>;
+
+bool DBCSHasFoldMap(int codePage);
+void DBCSSetFoldMap(int codePage, const FoldMap &foldMap);
+FoldMap *DBCSGetMutableFoldMap(int codePage);
+const FoldMap *DBCSGetFoldMap(int codePage);
+
 }
 
 #endif