refactor block

src/lib.rs

@@ -38,6 +38,10 @@ impl Block {
 
     pub fn advance(&mut self) {
         self.counter += 1;
+        self.compute_block();
+    }
+
+    fn compute_block(&mut self) {
         self.chunk = few_u32_to_many_u8(&chacha_block(&self.key, self.counter, self.nonce, self.rounds));
     }
 
@@ -53,6 +57,12 @@ impl Block {
             }
         }
     }
+
+    pub fn reset(&mut self, next_nonce: [u32; 3]) {
+        self.counter = 0;
+        self.nonce = next_nonce;
+        self.compute_block();
+    }
 }
 
 #[inline]