bgzf/multithreaded_reader: Directly copy from the block buffer when t…

…he given buffer can be completely filled

noodles-bgzf/src/multithreaded_reader.rs

@@ -275,6 +275,18 @@ where
         self.consume(amt);
         Ok(amt)
     }
+
+    fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
+        use super::reader::default_read_exact;
+
+        if let Some(src) = self.buffer.block.data().as_ref().get(..buf.len()) {
+            buf.copy_from_slice(src);
+            self.consume(src.len());
+            Ok(())
+        } else {
+            default_read_exact(self, buf)
+        }
+    }
 }
 
 impl<R> BufRead for MultithreadedReader<R>

noodles-bgzf/src/reader.rs

@@ -295,7 +295,7 @@ where
     }
 }
 
-fn default_read_exact<R>(reader: &mut R, mut buf: &mut [u8]) -> io::Result<()>
+pub(crate) fn default_read_exact<R>(reader: &mut R, mut buf: &mut [u8]) -> io::Result<()>
 where
     R: Read,
 {