25% speed improvement in filter mode 2 by using iter instead of for

CHANGELOG.md

@@ -1,5 +1,6 @@
 **Version 0.6.1 (unreleased)**
  - Minor compression improvement on interlaced images
+ - Performance optimizations
 
 **Version 0.6.0**
  - Fix issue where output directory would not be created if it did not exist

Cargo.toml

@@ -21,6 +21,9 @@ name = "oxipng"
 path = "src/main.rs"
 doc = false
 
+[profile.release]
+debug = true
+
 [dependencies]
 bit-vec = "^0.4.2"
 byteorder = "^0.5.0"

src/png.rs

@@ -1081,13 +1081,14 @@ fn filter_line(filter: u8, bpp: usize, data: &[u8], last_line: &[u8]) -> Vec<u8>
             }
         }
         2 => {
-            for (i, byte) in data.iter().enumerate() {
+            if last_line.is_empty() {
-                if last_line.is_empty() {
+                filtered.extend_from_slice(data);
-                    filtered.push(*byte);
+            } else {
-                } else {
+                filtered.extend_from_slice(&data.iter()
-                    filtered.push(byte.wrapping_sub(last_line[i]));
+                                                .zip(last_line.iter())
-                };
+                                                .map(|(cur, last)| cur.wrapping_sub(*last))
-            }
+                                                .collect::<Vec<u8>>());
+            };
         }
         3 => {
             for (i, byte) in data.iter().enumerate() {