openpgp: Optimize drop(Vec<u8>::drain(..n)) in debug mode.

  - Similar to Vec<u8>::truncate(_), this operation is very slow in
    debug mode due to the dropping of drained elements.  Provide an
    optimized version in debug mode.

1 files changed, 2 insertions, 2 deletions

diff --git a/openpgp/src/crypto/aead.rs b/openpgp/src/crypto/aead.rs
index 35fbd074..a297b999 100644
--- a/openpgp/src/crypto/aead.rs
+++ b/openpgp/src/crypto/aead.rs
@@ -223,7 +223,7 @@ impl<'a> Decryptor<'a> {
         if self.buffer.len() > 0 {
             let to_copy = cmp::min(self.buffer.len(), plaintext.len());
             &plaintext[..to_copy].copy_from_slice(&self.buffer[..to_copy]);
-            self.buffer.drain(..to_copy);
+            crate::vec_drain_prefix(&mut self.buffer, to_copy);
 
             pos = to_copy;
             if pos == plaintext.len() {
@@ -341,7 +341,7 @@ impl<'a> Decryptor<'a> {
 
                     &plaintext[pos..pos + to_copy]
                         .copy_from_slice(&self.buffer[..to_copy]);
-                    self.buffer.drain(..to_copy);
+                    crate::vec_drain_prefix(&mut self.buffer, to_copy);
                     pos += to_copy;
                 } else {
                     pos += to_decrypt;