Reuse ringbuffer in Reader.

Fixes #33

brotli_test.go

@@ -345,6 +345,22 @@ func TestReader(t *testing.T) {
 			"<%d bytes>",
 			got, len(content))
 	}
+
+	r.Reset(bytes.NewReader(encoded))
+	decodedOutput.Reset()
+	n, err = io.Copy(&decodedOutput, r)
+	if err != nil {
+		t.Fatalf("After Reset: Copy(): n=%v, err=%v", n, err)
+	}
+	if got := decodedOutput.Bytes(); !bytes.Equal(got, content) {
+		t.Errorf("After Reset: "+
+			"Reader output:\n"+
+			"%q\n"+
+			"want:\n"+
+			"<%d bytes>",
+			got, len(content))
+	}
+
 }
 
 func TestDecode(t *testing.T) {

decode.go

@@ -1304,26 +1304,21 @@ func wrapRingBuffer(s *Reader) {
    Last two bytes of ring-buffer are initialized to 0, so context calculation
    could be done uniformly for the first two and all other positions. */
 func ensureRingBuffer(s *Reader) bool {
-	var old_ringbuffer []byte = s.ringbuffer
+	var old_ringbuffer []byte
 	if s.ringbuffer_size == s.new_ringbuffer_size {
 		return true
 	}
-
-	s.ringbuffer = make([]byte, uint(s.new_ringbuffer_size)+uint(kRingBufferWriteAheadSlack))
-	if s.ringbuffer == nil {
-		/* Restore previous value. */
-		s.ringbuffer = old_ringbuffer
-
-		return false
+	spaceNeeded := int(s.new_ringbuffer_size) + int(kRingBufferWriteAheadSlack)
+	if len(s.ringbuffer) < spaceNeeded {
+		old_ringbuffer = s.ringbuffer
+		s.ringbuffer = make([]byte, spaceNeeded)
 	}
 
 	s.ringbuffer[s.new_ringbuffer_size-2] = 0
 	s.ringbuffer[s.new_ringbuffer_size-1] = 0
 
-	if !(old_ringbuffer == nil) {
+	if old_ringbuffer != nil {
 		copy(s.ringbuffer, old_ringbuffer[:uint(s.pos)])
-
-		old_ringbuffer = nil
 	}
 
 	s.ringbuffer_size = s.new_ringbuffer_size

state.go

@@ -200,7 +200,6 @@ func decoderStateInit(s *Reader) bool {
 
 	s.block_type_trees = nil
 	s.block_len_trees = nil
-	s.ringbuffer = nil
 	s.ringbuffer_size = 0
 	s.new_ringbuffer_size = 0
 	s.ringbuffer_mask = 0