Merge pull request #156 from Shnatsel/should-filter-bounds-check

Eliminate bounds checks from simple_threshold_horizontal()

Author: Shnatsel

src/loop_filter.rs

@@ -89,6 +89,7 @@ fn simple_threshold_vertical(
 
 #[inline]
 fn simple_threshold_horizontal(filter_limit: i32, pixels: &[u8]) -> bool {
+    assert!(pixels.len() >= 6); // one bounds check up front eliminates all subsequent checks in this function
     i32::from(diff(pixels[3], pixels[4])) * 2 + i32::from(diff(pixels[2], pixels[5])) / 2
         <= filter_limit
 }
@@ -113,6 +114,7 @@ fn should_filter_vertical(
 }
 
 fn should_filter_horizontal(interior_limit: u8, edge_limit: u8, pixels: &[u8]) -> bool {
+    assert!(pixels.len() >= 8); // one bounds check up front eliminates all subsequent checks in this function
     simple_threshold_horizontal(i32::from(edge_limit), pixels)
         // this looks like an erroneous way to compute differences between 8 points, but isn't:
         // there are actually only 6 diff comparisons required as per the spec: