From 4eca2124896b93b8a542811edeb9d930bdae0668 Mon Sep 17 00:00:00 2001
From: Zufu Liu <unknown>
Date: Sun, 17 Nov 2024 10:08:59 +1100
Subject: Feature [feature-requests:#1533]. More performance for SCI_BRACEMATCH
 by avoiding costly NextPosition call where possible. Approximately 60%
 improvement on tested system.

---
 src/Document.cxx | 48 +++++++++++++++++++++++++++++++++++++++++-------
 src/Document.h   |  1 +
 2 files changed, 42 insertions(+), 7 deletions(-)

diff --git a/src/Document.cxx b/src/Document.cxx
index ef8bfce4d..0b34d5e73 100644
--- a/src/Document.cxx
+++ b/src/Document.cxx
@@ -1170,6 +1170,29 @@ bool Document::IsDBCSTrailByteNoExcept(char ch) const noexcept {
 	return false;
 }
 
+unsigned char Document::DBCSMinTrailByte() const noexcept {
+	switch (dbcsCodePage) {
+	case 932:
+		// Shift_jis
+		return 0x40;
+	case 936:
+		// GBK
+		return 0x40;
+	case 949:
+		// Korean Wansung KS C-5601-1987
+		return 0x41;
+	case 950:
+		// Big5
+		return 0x40;
+	case 1361:
+		// Korean Johab KS C-5601-1992
+		return 0x31;
+	default:
+		// UTF-8 or single byte, should not occur as not DBCS
+		return 0;
+	}
+}
+
 int Document::DBCSDrawBytes(std::string_view text) const noexcept {
 	if (text.length() <= 1) {
 		return static_cast<int>(text.length());
@@ -2828,8 +2851,8 @@ static char BraceOpposite(char ch) noexcept {
 
 // TODO: should be able to extend styled region to find matching brace
 Sci::Position Document::BraceMatch(Sci::Position position, Sci::Position /*maxReStyle*/, Sci::Position startPos, bool useStartPos) noexcept {
-	const char chBrace = CharAt(position);
-	const char chSeek = BraceOpposite(chBrace);
+	const unsigned char chBrace = CharAt(position);
+	const unsigned char chSeek = BraceOpposite(chBrace);
 	if (chSeek == '\0')
 		return - 1;
 	const int styBrace = StyleIndexAt(position);
@@ -2838,8 +2861,15 @@ Sci::Position Document::BraceMatch(Sci::Position position, Sci::Position /*maxRe
 		direction = 1;
 	int depth = 1;
 	position = useStartPos ? startPos : NextPosition(position, direction);
+
+	// Avoid complex NextPosition call for bytes that may not cause incorrect match
+	unsigned char maxSafeChar = 0xff;
+	if (dbcsCodePage != 0 && dbcsCodePage != CpUtf8) {
+		maxSafeChar = (direction >= 0) ? 0x80 : DBCSMinTrailByte() - 1;
+	}
+
 	while ((position >= 0) && (position < LengthNoExcept())) {
-		const char chAtPos = CharAt(position);
+		const unsigned char chAtPos = CharAt(position);
 		if (chAtPos == chBrace || chAtPos == chSeek) {
 			if ((position > GetEndStyled()) || (StyleIndexAt(position) == styBrace)) {
 				depth += (chAtPos == chBrace) ? 1 : -1;
@@ -2847,10 +2877,14 @@ Sci::Position Document::BraceMatch(Sci::Position position, Sci::Position /*maxRe
 					return position;
 			}
 		}
-		const Sci::Position positionBeforeMove = position;
-		position = NextPosition(position, direction);
-		if (position == positionBeforeMove)
-			break;
+		if (chAtPos <= maxSafeChar) {
+			position += direction;
+		} else {
+			const Sci::Position positionBeforeMove = position;
+			position = NextPosition(position, direction);
+			if (position == positionBeforeMove)
+				break;
+		}
 	}
 	return - 1;
 }
diff --git a/src/Document.h b/src/Document.h
index 01c608d0e..cecf02899 100644
--- a/src/Document.h
+++ b/src/Document.h
@@ -369,6 +369,7 @@ public:
 	bool SCI_METHOD IsDBCSLeadByte(char ch) const override;
 	bool IsDBCSLeadByteNoExcept(char ch) const noexcept;
 	bool IsDBCSTrailByteNoExcept(char ch) const noexcept;
+	unsigned char DBCSMinTrailByte() const noexcept;
 	int DBCSDrawBytes(std::string_view text) const noexcept;
 	bool IsDBCSDualByteAt(Sci::Position pos) const noexcept;
 	size_t SafeSegment(std::string_view text) const noexcept;
-- 
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