openpgp,buffered-reader: Optimize Vec<u8>::truncate manually

  - On debug builds, Vec<u8>::truncate is very, very slow.  For
    instance, running the decrypt_test_stream test takes 51 seconds on
    my (Neal's) computer using Vec<u8>::truncate and <0.1 seconds using
    `unsafe { v.set_len(len); }`.

    The issue is that the compiler calls drop on every element that is
    dropped, even though a u8 doesn't have a drop implementation.  The
    compiler optimizes this away at high optimization levels, but
    those levels make debugging harder.

1 files changed, 1 insertions, 2 deletions

diff --git a/buffered-reader/src/generic.rs b/buffered-reader/src/generic.rs
index de1a52c7..7b5dd540 100644
--- a/buffered-reader/src/generic.rs
+++ b/buffered-reader/src/generic.rs
@@ -131,7 +131,6 @@ impl<T: io::Read, C> Generic<T, C> {
 
             if amount_read > 0 {
                 // We read something.
-
                 if let Some(ref buffer) = self.buffer {
                     // We need to copy in the old data.
                     buffer_new[0..amount_buffered]
@@ -139,7 +138,7 @@ impl<T: io::Read, C> Generic<T, C> {
                             &buffer[self.cursor..self.cursor + amount_buffered]);
                 }
 
-                buffer_new.truncate(amount_buffered + amount_read);
+                vec_truncate(&mut buffer_new, amount_buffered + amount_read);
                 buffer_new.shrink_to_fit();
 
                 self.buffer = Some(buffer_new.into_boxed_slice());