Difference between pages "Module:String" and "Module:String/sandbox"

(Difference between pages)

@@ Line 165: / Line 165: @@
 		end
-		local iterator = mw.ustring.gmatch(s, pattern)
+		local iterator = mw.ustring.gmatch( s, pattern )
 		if match_index > 0 then
 			-- Forward search
@@ Line 177: / Line 177: @@
 		else
 			-- Reverse search
-			local result_table = {}
+			local match_buffer = {}
-			local count = 1
+			local index = 1
+			match_index = -match_index
 			for w in iterator do
-				result_table[count] = w
+				match_buffer[index] = w
-				count = count + 1
+				-- Circular buffer with length 'match_index'
+				-- Wraps around to overwrite matches too old to be the result,
+				-- so memory use is O(match_index) and not O(total match count))
+				index = (index == match_index) and 1 or (index + 1)
 			end
-			result = result_table[ count + match_index ]
+			-- 'index' is now at oldest element, which next iteration would have
+			-- overwritten. If 'match_buffer' has fewer than 'index' elements,
+			-- there were too few matches; the resulting nil is handled below.
+			result = match_buffer[index]
 		end
 	end