Cover VectorFastPFOR with the shared codec test suites

SkippableBasicTest exercises maxHeadlessCompressedLength, so implement it
(mirroring FastPFOR) rather than throwing.

Author: raunaqmorarka

src/main/java/me/lemire/integercompression/vector/VectorFastPFOR.java

@@ -54,6 +54,8 @@
  */
 public class VectorFastPFOR implements IntegerCODEC, SkippableIntegerCODEC {
   private final static int OVERHEAD_OF_EACH_EXCEPT = 8;
+  private static final int OVERHEAD_OF_EACH_PAGE_IN_INTS = 36;
+  private static final int OVERHEAD_OF_EACH_BLOCK_IN_INTS = 1;
   public final static int DEFAULT_PAGE_SIZE = 64 << 10;
 
   public final static int BLOCK_SIZE = 256;
@@ -257,7 +259,11 @@ public void headlessUncompress(int[] in, IntWrapper inpos, int inlength,
 
   @Override
   public int maxHeadlessCompressedLength(IntWrapper compressedPositions, int inlength) {
-    throw new UnsupportedOperationException("Calculating the max compressed length is not supported yet.");
+    inlength = inlength - inlength % BLOCK_SIZE;
+    int pageCount = (inlength + pageSize - 1) / pageSize;
+    int blockCount = inlength / BLOCK_SIZE;
+    int blockSizeInInts = OVERHEAD_OF_EACH_BLOCK_IN_INTS + BLOCK_SIZE;
+    return OVERHEAD_OF_EACH_PAGE_IN_INTS * pageCount + blockSizeInInts * blockCount + 24;
   }
 
   private void loadMetaData(int[] in, int inexcept, int bytesize) {

src/test/java/me/lemire/integercompression/BasicTest.java

@@ -17,6 +17,7 @@
 import me.lemire.integercompression.differential.IntegratedVariableByte;
 import me.lemire.integercompression.differential.XorBinaryPacking;
 import me.lemire.integercompression.synth.ClusteredDataGenerator;
+import me.lemire.integercompression.vector.VectorFastPFOR;
 
 import org.junit.Test;
 
@@ -43,6 +44,7 @@ public class BasicTest {
             new Composition(new OptPFDS16(), new VariableByte()),
             new Composition(new FastPFOR128(), new VariableByte()),
             new Composition(new FastPFOR(), new VariableByte()),
+            new Composition(new VectorFastPFOR(), new VariableByte()),
             new Simple9(),
             new Simple16(),
             new GroupSimple9(),

src/test/java/me/lemire/integercompression/SkippableBasicTest.java

@@ -13,6 +13,7 @@
 import me.lemire.integercompression.differential.IntegratedVariableByte;
 import me.lemire.integercompression.differential.SkippableIntegratedComposition;
 import me.lemire.integercompression.differential.SkippableIntegratedIntegerCODEC;
+import me.lemire.integercompression.vector.VectorFastPFOR;
 import org.junit.Test;
 
 import static org.junit.Assert.assertArrayEquals;
@@ -37,6 +38,7 @@ public class SkippableBasicTest {
             new SkippableComposition(new OptPFDS16(), new VariableByte()),
             new SkippableComposition(new FastPFOR128(), new VariableByte()),
             new SkippableComposition(new FastPFOR(), new VariableByte()),
+            new SkippableComposition(new VectorFastPFOR(), new VariableByte()),
             new Simple9(),
             new Simple16() };