fix overflow for long messages

1 files changed, 11 insertions, 0 deletions

diff --git a/src/block.rs b/src/block.rs
index e63062e..abd7ff7 100644
--- a/src/block.rs
+++ b/src/block.rs
@@ -53,6 +53,17 @@ impl Block {
         }
         Block(block)
     }
+
+    /// Computes self * 2^exponent
+    ///
+    /// Ensures that there's no overflow in computing 2^exponent.
+    pub fn exp(&self, exponent: u32) -> Block {
+        match exponent {
+            _ if exponent < 32 => *self * (1 << exponent),
+            _ if exponent % 2 == 0 => self.exp(exponent / 2).exp(exponent / 2),
+            _ => (*self * 2).exp(exponent - 1),
+        }
+    }
 }
 
 impl From<[u8; 16]> for Block {