Replace RingBuffer internals with VecDeque

src/decoding/decodebuffer.rs

@@ -107,20 +107,7 @@ impl DecodeBuffer {
                 // We need to copy in chunks.
                 self.repeat_in_chunks(offset, match_length, start_idx);
             } else {
-                // can just copy parts of the existing buffer
-                // SAFETY: Requirements checked:
-                // 1. start_idx + match_length must be <= self.buffer.len()
-                //      We know that:
-                //      1. start_idx = self.buffer.len() - offset
-                //      2. end_idx = start_idx + match_length
-                //      3. end_idx <= self.buffer.len()
-                //      Thus follows: start_idx + match_length <= self.buffer.len()
-                //
-                // 2. explicitly reserved enough memory for the whole match_length
-                unsafe {
-                    self.buffer
-                        .extend_from_within_unchecked(start_idx, match_length)
-                };
+                self.buffer.extend_from_within(start_idx, match_length);
             }
 
             self.total_output_counter += match_length as u64;
@@ -137,22 +124,7 @@ impl DecodeBuffer {
         while copied_counter_left > 0 {
             let chunksize = usize::min(offset, copied_counter_left);
 
-            // SAFETY: Requirements checked:
-            // 1. start_idx + chunksize must be <= self.buffer.len()
-            //      We know that:
-            //      1. start_idx starts at buffer.len() - offset
-            //      2. chunksize <= offset (== offset for each iteration but the last, and match_length modulo offset in the last iteration)
-            //      3. the buffer grows by offset many bytes each iteration but the last
-            //      4. start_idx is increased by the same amount as the buffer grows each iteration
-            //
-            //      Thus follows: start_idx + chunksize == self.buffer.len() in each iteration but the last, where match_length modulo offset == chunksize < offset
-            //          Meaning: start_idx + chunksize <= self.buffer.len()
-            //
-            // 2. explicitly reserved enough memory for the whole match_length
-            unsafe {
-                self.buffer
-                    .extend_from_within_unchecked(start_idx, chunksize)
-            };
+            self.buffer.extend_from_within(start_idx, chunksize);
             copied_counter_left -= chunksize;
             start_idx += chunksize;
         }