Update README.adoc for 2.1.0, finalize certain values and make getLon…

…gArray() to return a reference instead of a copy of the underlying on-heap array

README.adoc

@@ -37,18 +37,20 @@ You can find latest version from the maven logo link above.
 === Compressing
 
 To compress in the older 1.x format, use class ``Compressor``. For 2.x, use ``GorillaCompressor`` (recommended).
-``ByteBufferLongOutput`` is also recommended compared to ``ByteBufferBitOutput`` because of performance.
+``LongArrayOutput`` is also recommended compared to ``ByteBufferBitOutput`` because of performance. One can supply
+alternative predictor to the ``GorillaCompressor`` if required. One such implementation is included,
+``DifferentialFCM`` that provides better compression ratio for some data patterns.
 
 [source, java]
 ----
 long now = LocalDateTime.now(ZoneOffset.UTC).truncatedTo(ChronoUnit.HOURS)
         .toInstant(ZoneOffset.UTC).toEpochMilli();
 
-ByteBufferLongOutput output = new ByteBufferLongOutput();
+LongArrayOutput output = new LongArrayOutput();
 GorillaCompressor c = new GorillaCompressor(now, output);
 ----
 
-Compression class requires a block timestamp and an implementation of `BitOutput` interface. `ByteBufferLongOutput` is an in-memory example that uses off-heap storage.
+Compression class requires a block timestamp and an implementation of `BitOutput` interface.
 
 [source, java]
 ----
@@ -70,17 +72,18 @@ which flushes the remaining data to the stream and writes closing information.
 === Decompressing
 
 To decompress from the older 1.x format, use class ``Decompressor``. For 2.x, use ``GorillaDecompressor`` (recommended).
-``ByteBufferLongInput`` is also recommended compared to ``ByteBufferBitInput`` because of performance if the 2.x
-format was used to compress the time series.
+``LongArrayInput`` is also recommended compared to ``ByteBufferBitInput`` because of performance if the 2.x
+format was used to compress the time series. If the original compressor used different predictor than
+``LastValuePredictor`` it must be defined in the constructor.
 
 [source, java]
 ----
-ByteBufferLongInput input = new ByteBufferLongInput(byteBuffer);
+LongArrayInput input = new LongArrayInput(byteBuffer);
 GorillaDecompressor d = new GorillaDecompressor(input);
 ----
 
 To decompress a stream of bytes, supply `GorillaDecompressor` with a suitable implementation of `BitInput` interface.
- The ByteBufferLongInput allows to decompress a long array or existing `ByteBuffer` presentation with 8 byte word
+ The LongArrayInput allows to decompress a long array or existing `ByteBuffer` presentation with 8 byte word
  length.
 
 [source, java]
@@ -125,12 +128,10 @@ not from the small changes to the output format.
 There were few things I wanted to get to 2.0.0, but had to decide against due to lack of time. I will implement these
  later with potentially some breaking API changes:
 
- * Support timestamp only and value only compressions (2.1.x)
- * Support for Java 8 streams in decompression and compression API (2.1.x)
- * Change delta-of-delta ranges based on some real-world results when using millisecond resolution (3.0.x)
+ * Support timestamp only compressions (2.2.x)
+ * Include ByteBufferLongOutput/ByteBufferLongInput in the package (2.2.x)
  * Move bit operations to inside the GorillaCompressor/GorillaDecompressor to allow easier usage with
- Netty's ByteBuf and allocator (or Agrona etc). (3.0.x)
-   ** Example for Netty: https://gist.github.com/burmanm/d6ad33089aaf78104d5f0f7977f097ce
+ other allocators (2.2.x)
 
 == Internals
 
@@ -157,7 +158,7 @@ File an issue and/or send a pull request.
 === License
 
 ....
-   Copyright 2016-2017 Michael Burman and/or other contributors.
+   Copyright 2016-2018 Michael Burman and/or other contributors.
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.

src/main/java/fi/iki/yak/ts/compression/gorilla/GorillaDecompressor.java

@@ -1,5 +1,7 @@
 package fi.iki.yak.ts.compression.gorilla;
 
+import java.util.stream.Stream;
+
 import fi.iki.yak.ts.compression.gorilla.predictors.LastValuePredictor;
 
 /**
@@ -15,8 +17,8 @@ public class GorillaDecompressor {
     private long storedVal = 0;
     private boolean endOfStream = false;
 
-    private BitInput in;
-    private ValueDecompressor decompressor;
+    private final BitInput in;
+    private final ValueDecompressor decompressor;
 
     public GorillaDecompressor(BitInput input) {
         this(input, new LastValuePredictor());
@@ -125,5 +127,4 @@ public static int decodeZigZag32(final int n) {
     }
 
     // END: From protobuf
-
 }

src/main/java/fi/iki/yak/ts/compression/gorilla/LongArrayInput.java

@@ -22,7 +22,7 @@
  * @author Michael Burman
  */
 public class LongArrayInput implements BitInput {
-    private long[] longArray; // TODO Investigate also the ByteBuffer performance here.. or Unsafe
+    private final long[] longArray; // TODO Investigate also the ByteBuffer performance here.. or Unsafe
     private long lB;
     private int position = 0;
     private int bitsLeft = 0;

src/main/java/fi/iki/yak/ts/compression/gorilla/LongArrayOutput.java

@@ -6,7 +6,7 @@
  * @author Michael Burman
  */
 public class LongArrayOutput implements BitOutput {
-    public static final int DEFAULT_ALLOCATION =  4096*32;
+    public static final int DEFAULT_ALLOCATION = 256;
 
     private long[] longArray;
     private int position = 0;
@@ -129,22 +129,17 @@ public void writeBits(long value, int bits) {
     }
 
     /**
-     * Causes the currently handled byte to be written to the stream
+     * Causes the currently handled word to be written to the stream
      */
     @Override
     public void flush() {
-        flipWord(); // Causes write to the ByteBuffer
-    }
-
-    public void reset() {
-        position = 0;
-        bitsLeft = Long.SIZE;
-        lB = 0;
+        flipWord();
     }
 
+    /**
+     * Changed in 2.1, returns a reference to the underlying array (no copy anymore)
+     */
     public long[] getLongArray() {
-        long[] copy = new long[position+1];
-        System.arraycopy(longArray, 0, copy, 0, position);
-        return copy;
+        return this.longArray;
     }
 }

src/main/java/fi/iki/yak/ts/compression/gorilla/ValueDecompressor.java

@@ -8,8 +8,8 @@
  * @author Michael Burman
  */
 public class ValueDecompressor {
-    private BitInput in;
-    private Predictor predictor;
+    private final BitInput in;
+    private final Predictor predictor;
 
     private int storedLeadingZeros = Integer.MAX_VALUE;
     private int storedTrailingZeros = 0;

src/main/java/fi/iki/yak/ts/compression/gorilla/predictors/DifferentialFCM.java

@@ -10,7 +10,7 @@
 public class DifferentialFCM implements Predictor {
 
     private long lastValue = 0L;
-    private long[] table;
+    private final long[] table;
     private int lastHash = 0;
 
     private final int mask;
@@ -29,7 +29,7 @@ public DifferentialFCM(int size) {
             this.table = new long[newSize];
             this.mask = newSize - 1;
         } else {
-            throw new IllegalArgumentException("Size must be positive and a power of two");
+            throw new IllegalArgumentException("Size must be positive");
         }
     }