manually implement addition-by-one

The int conversion is quite costly, so this is a lot faster (especially
in the non-simd build).

1 files changed, 16 insertions, 0 deletions

diff --git a/src/block.rs b/src/block.rs
index 96c3496..8327286 100644
--- a/src/block.rs
+++ b/src/block.rs
@@ -12,6 +12,18 @@ pub struct Block(u8x16);
 #[cfg(not(feature = "simd"))]
 pub struct Block([u8; 16]);
 
+macro_rules! add_ladder {
+    ($ar:expr, $lit:literal) => {
+        $ar[$lit] = $ar[$lit].wrapping_add(1);
+    };
+    ($ar:expr, $lit:literal $($rest:literal) +) => {
+        $ar[$lit] = $ar[$lit].wrapping_add(1);
+        if $ar[$lit] == 0 {
+            add_ladder!($ar, $($rest) +);
+        }
+    };
+}
+
 impl Block {
     pub fn null() -> Block {
         Block([0; 16].into())
@@ -95,6 +107,10 @@ impl Block {
             _ => (*self * 2).exp(exponent - 1),
         }
     }
+
+    pub fn count_up(&mut self) {
+        add_ladder!(self, 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0);
+    }
 }
 
 impl From<[u8; 16]> for Block {