Bug [#2340]. Avoid repeated call in GetFoldParent for around 10% performance

gain with Visual C++ 64-bit release mode on 300,000 line file.
Remove duplicated code and simplify.
GetFoldLevel and thus GetFoldParent can't throw so mark as noexcept.

2 files changed, 10 insertions, 16 deletions

diff --git a/src/Document.cxx b/src/Document.cxx
index 00ac8e618..2d1acd7e1 100644
--- a/src/Document.cxx
+++ b/src/Document.cxx
@@ -558,7 +558,7 @@ int SCI_METHOD Document::GetLevel(Sci_Position line) const {
 	return Levels()->GetLevel(line);
 }
 
-FoldLevel Document::GetFoldLevel(Sci_Position line) const {
+FoldLevel Document::GetFoldLevel(Sci_Position line) const noexcept {
 	return static_cast<FoldLevel>(Levels()->GetLevel(line));
 }
 
@@ -597,21 +597,15 @@ Sci::Line Document::GetLastChild(Sci::Line lineParent, std::optional<FoldLevel>
 	return lineMaxSubord;
 }
 
-Sci::Line Document::GetFoldParent(Sci::Line line) const {
+Sci::Line Document::GetFoldParent(Sci::Line line) const noexcept {
 	const FoldLevel level = LevelNumberPart(GetFoldLevel(line));
-	Sci::Line lineLook = line - 1;
-	while ((lineLook > 0) && (
-	            (!LevelIsHeader(GetFoldLevel(lineLook))) ||
-	            (LevelNumberPart(GetFoldLevel(lineLook)) >= level))
-	      ) {
-		lineLook--;
-	}
-	if (LevelIsHeader(GetFoldLevel(lineLook)) &&
-	        (LevelNumberPart(GetFoldLevel(lineLook)) < level)) {
-		return lineLook;
-	} else {
-		return -1;
+	for (Sci::Line lineLook = line - 1; lineLook >= 0; lineLook--) {
+		const FoldLevel levelTry = GetFoldLevel(lineLook);
+		if (LevelIsHeader(levelTry) && LevelNumberPart(levelTry) < level) {
+			return lineLook;
+		}
 	}
+	return -1;
 }
 
 void Document::GetHighlightDelimiters(HighlightDelimiter &highlightDelimiter, Sci::Line line, Sci::Line lastLine) {
diff --git a/src/Document.h b/src/Document.h
index 3b0c8ab5a..8d5643e90 100644
--- a/src/Document.h
+++ b/src/Document.h
@@ -461,10 +461,10 @@ public:
 
 	int SCI_METHOD SetLevel(Sci_Position line, int level) override;
 	int SCI_METHOD GetLevel(Sci_Position line) const override;
-	Scintilla::FoldLevel GetFoldLevel(Sci_Position line) const;
+	Scintilla::FoldLevel GetFoldLevel(Sci_Position line) const noexcept;
 	void ClearLevels();
 	Sci::Line GetLastChild(Sci::Line lineParent, std::optional<Scintilla::FoldLevel> level = {}, Sci::Line lastLine = -1);
-	Sci::Line GetFoldParent(Sci::Line line) const;
+	Sci::Line GetFoldParent(Sci::Line line) const noexcept;
 	void GetHighlightDelimiters(HighlightDelimiter &highlightDelimiter, Sci::Line line, Sci::Line lastLine);
 
 	Sci::Position ExtendWordSelect(Sci::Position pos, int delta, bool onlyWordCharacters=false) const;