From fde8cbc171d35ab1990d2060a47df603bda928ec Mon Sep 17 00:00:00 2001
From: Tobias Koppers <tobias.koppers@googlemail.com>
Date: Mon, 2 Aug 2021 11:29:53 +0200
Subject: [PATCH] improve performance of mappings serialization

---
 lib/helpers/createMappingsSerializer.js | 87 +++++++++++++++++--------
 1 file changed, 59 insertions(+), 28 deletions(-)

diff --git a/lib/helpers/createMappingsSerializer.js b/lib/helpers/createMappingsSerializer.js
index e554b16..8dafe43 100644
--- a/lib/helpers/createMappingsSerializer.js
+++ b/lib/helpers/createMappingsSerializer.js
@@ -70,10 +70,6 @@ const createFullMappingsSerializer = () => {
 		}
 
 		const writeValue = value => {
-			if (value === 0) {
-				str += "A";
-				return;
-			}
 			const sign = (value >>> 31) & 1;
 			const mask = value >> 31;
 			const absValue = (value + mask) ^ mask;
@@ -93,12 +89,20 @@ const createFullMappingsSerializer = () => {
 		currentColumn = generatedColumn;
 		if (sourceIndex >= 0) {
 			activeMapping = true;
-			writeValue(sourceIndex - currentSourceIndex);
-			currentSourceIndex = sourceIndex;
+			if (sourceIndex === currentSourceIndex) {
+				str += "A";
+			} else {
+				writeValue(sourceIndex - currentSourceIndex);
+				currentSourceIndex = sourceIndex;
+			}
 			writeValue(originalLine - currentOriginalLine);
 			currentOriginalLine = originalLine;
-			writeValue(originalColumn - currentOriginalColumn);
-			currentOriginalColumn = originalColumn;
+			if (originalColumn === currentOriginalColumn) {
+				str += "A";
+			} else {
+				writeValue(originalColumn - currentOriginalColumn);
+				currentOriginalColumn = originalColumn;
+			}
 			if (nameIndex >= 0) {
 				writeValue(nameIndex - currentNameIndex);
 				currentNameIndex = nameIndex;
@@ -126,24 +130,16 @@ const createLinesOnlyMappingsSerializer = () => {
 		_originalColumn,
 		_nameIndex
 	) => {
-		let str = "";
 		if (sourceIndex < 0) {
 			// avoid writing generated mappings at all
-			return str;
+			return "";
 		}
 		if (lastWrittenLine === generatedLine) {
 			// avoid writing multiple original mappings per line
-			return str;
-		}
-		while (currentLine < generatedLine) {
-			str += ";";
-			currentLine++;
+			return "";
 		}
+		let str;
 		const writeValue = value => {
-			if (value === 0) {
-				str += "A";
-				return;
-			}
 			const sign = (value >>> 31) & 1;
 			const mask = value >> 31;
 			const absValue = (value + mask) ^ mask;
@@ -159,16 +155,51 @@ const createLinesOnlyMappingsSerializer = () => {
 				}
 			}
 		};
-		str += "A";
-		if (sourceIndex >= 0) {
-			lastWrittenLine = currentLine;
-			writeValue(sourceIndex - currentSourceIndex);
-			currentSourceIndex = sourceIndex;
-			writeValue(originalLine - currentOriginalLine);
-			currentOriginalLine = originalLine;
-			str += "A";
+		lastWrittenLine = generatedLine;
+		if (generatedLine === currentLine + 1) {
+			currentLine = generatedLine;
+			if (sourceIndex === currentSourceIndex) {
+				currentSourceIndex = sourceIndex;
+				if (originalLine === currentOriginalLine + 1) {
+					currentOriginalLine = originalLine;
+					return ";AACA";
+				} else {
+					str = ";AA";
+					writeValue(originalLine - currentOriginalLine);
+					currentOriginalLine = originalLine;
+					return str + "A";
+				}
+			} else {
+				str = ";A";
+				writeValue(sourceIndex - currentSourceIndex);
+				currentSourceIndex = sourceIndex;
+				writeValue(originalLine - currentOriginalLine);
+				currentOriginalLine = originalLine;
+				return str + "A";
+			}
+		} else {
+			str = ";".repeat(generatedLine - currentLine);
+			currentLine = generatedLine;
+			if (sourceIndex === currentSourceIndex) {
+				currentSourceIndex = sourceIndex;
+				if (originalLine === currentOriginalLine + 1) {
+					currentOriginalLine = originalLine;
+					return str + "AACA";
+				} else {
+					str += "AA";
+					writeValue(originalLine - currentOriginalLine);
+					currentOriginalLine = originalLine;
+					return str + "A";
+				}
+			} else {
+				str += "A";
+				writeValue(sourceIndex - currentSourceIndex);
+				currentSourceIndex = sourceIndex;
+				writeValue(originalLine - currentOriginalLine);
+				currentOriginalLine = originalLine;
+				return str + "A";
+			}
 		}
-		return str;
 	};
 };