Index: src/0dev.org/diff/diff.go
==================================================================
--- src/0dev.org/diff/diff.go
+++ src/0dev.org/diff/diff.go
@@ -90,17 +90,17 @@
 }
 
 // Finds the largest common substring by looking at the provided match matrix
 // starting from (bounds.x, bounds.y) with lengths bounds.lenX, bounds.lenY
 func largest(bounds box, mat matrix) (result match) {
-	for i := bounds.x; i < bounds.lenX; i++ {
+	for i := bounds.x; i < bounds.lenX && result.length <= (bounds.lenX-bounds.x); i++ {
 		var m match = search(i, bounds.y, bounds.lenX, bounds.lenY, mat)
 		if m.length > result.length {
 			result = m
 		}
 	}
-	for j := bounds.y + 1; j < bounds.lenY; j++ {
+	for j := bounds.y + 1; j < bounds.lenY && result.length <= (bounds.lenY-bounds.y); j++ {
 		var m match = search(bounds.x, j, bounds.lenX, bounds.lenY, mat)
 		if m.length > result.length {
 			result = m
 		}
 	}