Change ~index - 1 > 0 to ~index-1 >=0 to allow for the case where ~index is equal to 1.

Add unit test to cover the cross line number case to GetMappingEntryForGeneratedSourcePosition.

src/SourcemapToolkit.SourcemapParser/SourceMap.cs

@@ -60,9 +60,9 @@ namespace SourcemapToolkit.SourcemapParser
             {
                 // The BinarySearch method returns the bitwise complement of the nearest element that is larger than the desired element when there isn't a match.
                 // Based on tests with source maps generated with the Closure Compiler, we should consider the closest source position that is smaller than the target value when we don't have a match.
-                if ((~index) - 1 > 0 && ParsedMappings[(~index) - 1].GeneratedSourcePosition.IsEqualish(generatedSourcePosition))
+                if (~index - 1 >= 0 && ParsedMappings[~index - 1].GeneratedSourcePosition.IsEqualish(generatedSourcePosition))
                 {
-                    index = (~index) - 1;
+                    index = ~index - 1;
                 }
             }
 

tests/SourcemapToolkit.SourcemapParser.UnitTests/SourceMapUnitTests.cs

@@ -68,7 +68,7 @@ namespace SourcemapToolkit.SourcemapParser.UnitTests
 		}
 
 		[TestMethod]
-		public void GetMappingEntryForGeneratedSourcePosition_NoExactMatchHasSimilar_ReturnSimilarEntry()
+		public void GetMappingEntryForGeneratedSourcePosition_NoExactMatchHasSimilarOnSameLine_ReturnSimilarEntry()
 		{
 			// Arrange
 			SourceMap sourceMap = new SourceMap();
@@ -92,5 +92,31 @@ namespace SourcemapToolkit.SourcemapParser.UnitTests
 			// Asset
 			Assert.AreEqual(matchingMappingEntry, result);
 		}
-	}
+
+        [TestMethod]
+        public void GetMappingEntryForGeneratedSourcePosition_NoExactMatchHasSimilarOnDifferentLinesLine_ReturnSimilarEntry()
+        {
+            // Arrange
+            SourceMap sourceMap = new SourceMap();
+            MappingEntry matchingMappingEntry = new MappingEntry
+            {
+                GeneratedSourcePosition = new SourcePosition { ZeroBasedLineNumber = 23, ZeroBasedColumnNumber = 15 }
+            };
+            sourceMap.ParsedMappings = new List<MappingEntry>
+            {
+                new MappingEntry
+                {
+                    GeneratedSourcePosition = new SourcePosition {ZeroBasedLineNumber = 0, ZeroBasedColumnNumber = 0}
+                },
+                matchingMappingEntry
+            };
+            SourcePosition sourcePosition = new SourcePosition { ZeroBasedLineNumber = 24, ZeroBasedColumnNumber = 0 };
+
+            // Act
+            MappingEntry result = sourceMap.GetMappingEntryForGeneratedSourcePosition(sourcePosition);
+
+            // Asset
+            Assert.AreEqual(matchingMappingEntry, result);
+        }
+    }
 }