From aaf443fca7749c2c89c686f838ccbe1cedb059b0 Mon Sep 17 00:00:00 2001
From: Joshua Holmer <holmerj@uindy.edu>
Date: Mon, 2 May 2016 15:58:45 -0400
Subject: [PATCH] Similarly optimize unfilter mode 2

Unfilter mode 1 can't benefit from this optimization
because it modifies and reads from the same line of data
---
 src/png.rs | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/src/png.rs b/src/png.rs
index e694bdfe..be009855 100644
--- a/src/png.rs
+++ b/src/png.rs
@@ -1149,13 +1149,14 @@ fn unfilter_line(filter: u8, bpp: usize, data: &[u8], last_line: &[u8]) -> Vec<u
             }
         }
         2 => {
-            for (i, byte) in data.iter().enumerate() {
-                if last_line.is_empty() {
-                    unfiltered.push(*byte);
-                } else {
-                    unfiltered.push(byte.wrapping_add(last_line[i]));
-                };
-            }
+            if last_line.is_empty() {
+                unfiltered.extend_from_slice(data);
+            } else {
+                unfiltered.extend_from_slice(&data.iter()
+                                                  .zip(last_line.iter())
+                                                  .map(|(cur, last)| cur.wrapping_add(*last))
+                                                  .collect::<Vec<u8>>());
+            };
         }
         3 => {
             for (i, byte) in data.iter().enumerate() {