From 4ea5726c57704579c463d39d8b1e027f33ed5a00 Mon Sep 17 00:00:00 2001
From: Manas Ranjan Dikshit <manasdikshit48@gmail.com>
Date: Fri, 3 Apr 2026 00:46:55 +0530
Subject: [PATCH 1/2] Change Uint32Array to Int32Array in readMappings

---
 lib/helpers/readMappings.js | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/lib/helpers/readMappings.js b/lib/helpers/readMappings.js
index 28dcece..cdee520 100644
--- a/lib/helpers/readMappings.js
+++ b/lib/helpers/readMappings.js
@@ -35,8 +35,8 @@ const ccMax = ccToValue.length - 1;
  * @returns {void}
  */
 const readMappings = (mappings, onMapping) => {
-	// generatedColumn, [sourceIndex, originalLine, orignalColumn, [nameIndex]]
-	const currentData = new Uint32Array([0, 0, 1, 0, 0]);
+	// generatedColumn, [sourceIndex, originalLine, originalColumn, [nameIndex]]
+	const currentData = new Int32Array([0, 0, 1, 0, 0]);
 	let currentDataPos = 0;
 	// currentValue will include a sign bit at bit 0
 	let currentValue = 0;
@@ -116,5 +116,4 @@ const readMappings = (mappings, onMapping) => {
 		);
 	}
 };
-
 module.exports = readMappings;

From a0d0a0f6a6d5281e4e1528c19a0a710c07e302f3 Mon Sep 17 00:00:00 2001
From: Manas Ranjan Dikshit <manasdikshit48@gmail.com>
Date: Mon, 6 Apr 2026 23:49:25 +0530
Subject: [PATCH 2/2] Add tests for readMappings function

---
 test/readMapping.js | 76 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100644 test/readMapping.js

diff --git a/test/readMapping.js b/test/readMapping.js
new file mode 100644
index 0000000..d3cc54d
--- /dev/null
+++ b/test/readMapping.js
@@ -0,0 +1,76 @@
+"use strict";
+
+const readMappings = require("../lib/helpers/readMappings");
+
+describe("readMappings", () => {
+	it("should correctly decode negative VLQ deltas (backwards column references)", () => {
+		const mappings = [];
+
+		// Mapping with a negative column delta (backwards reference)
+		readMappings(
+			"AAKA;CAAC",
+			(
+				generatedLine,
+				generatedColumn,
+				sourceIndex,
+				originalLine,
+				originalColumn,
+				nameIndex,
+			) => {
+				mappings.push({
+					generatedLine,
+					generatedColumn,
+					sourceIndex,
+					originalLine,
+					originalColumn,
+					nameIndex,
+				});
+			},
+		);
+
+		expect(mappings).toHaveLength(2);
+
+		// First mapping: line 1, col 0, source 0, orig line 5, orig col 0
+		expect(mappings[0].generatedLine).toBe(1);
+		expect(mappings[0].generatedColumn).toBe(0);
+		expect(mappings[0].sourceIndex).toBe(0);
+		expect(mappings[0].originalLine).toBe(5);
+		expect(mappings[0].originalColumn).toBe(0);
+
+		// Second mapping: line 2 — negative delta on originalColumn (col goes backwards)
+		expect(mappings[1].generatedLine).toBe(2);
+		expect(mappings[1].generatedColumn).toBe(1);
+		expect(mappings[1].sourceIndex).toBe(1);
+		expect(mappings[1].originalLine).toBe(5);
+		expect(mappings[1].originalColumn).toBe(-1);
+	});
+
+	it("should handle mappings without source info", () => {
+		const mappings = [];
+
+		readMappings("A", (generatedLine, generatedColumn, sourceIndex) => {
+			mappings.push({ generatedLine, generatedColumn, sourceIndex });
+		});
+
+		expect(mappings).toHaveLength(1);
+		expect(mappings[0].generatedLine).toBe(1);
+		expect(mappings[0].generatedColumn).toBe(0);
+		expect(mappings[0].sourceIndex).toBe(-1);
+	});
+
+	it("should handle multiple lines", () => {
+		const mappings = [];
+
+		readMappings(
+			"AAAA;AACA;AACA",
+			(generatedLine, generatedColumn, sourceIndex, originalLine) => {
+				mappings.push({ generatedLine, generatedColumn, originalLine });
+			},
+		);
+
+		expect(mappings).toHaveLength(3);
+		expect(mappings[0].generatedLine).toBe(1);
+		expect(mappings[1].generatedLine).toBe(2);
+		expect(mappings[2].generatedLine).toBe(3);
+	});
+});