switch the byte prefix of DATE_INCREMENT and MEASUREMENT

Date increments have usually higher values. 
I had hoped to reduce the file size by a lot. But in my example data
with 44 million entries (real life data) it only reduced the storage 
size by 1.5%.
Also fixed a bug in PdbReader that prevented other values for the 
CONTINUATION byte.
Also added a small testing tool that prints the content of a pdb file.
It is not (yet) made available as standalone tool, but during
debugging sessions it is very useful.

performanceDb/src/main/java/org/lucares/performance/db/ByteType.java

@@ -4,9 +4,9 @@ enum ByteType {
 
 	CONTINUATION(ContinuationByte.CONTINUATION_BYTE_PREFIX), // 10000000
 
-	MEASUREMENT(1 << 6), // 01000000
+	DATE_INCREMENT(1 << 6), // 01000000
 
-	DATE_INCREMENT(1 << 5), // 00100000
+	MEASUREMENT(1 << 5), // 00100000
 
 	DATE_OFFSET(1 << 4), // 00010000
 
@@ -64,7 +64,7 @@ enum ByteType {
 		return firstBytePrefix == (theByte & prefixBits);
 	}
 
-	private long getPrefixBits() {
+	public long getPrefixBits() {
 		return (~getValueBits()) & 0xff;
 	}
 
@@ -77,4 +77,8 @@ enum ByteType {
 		}
 		return null;
 	}
+
+	public long getValue(final int aByte) {
+		return aByte & getValueBits();
+	}
 }

performanceDb/src/main/java/org/lucares/performance/db/PdbFileViewer.java

@@ -0,0 +1,42 @@
+package org.lucares.performance.db;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+
+import org.lucares.pdb.api.Tags;
+
+public class PdbFileViewer {
+	private static final Tags TAGS = Tags.create();
+
+	public static void main(final String[] args) throws FileNotFoundException, IOException {
+		final File file = new File(args[0]);
+		final PdbFile pdbFile = new PdbFile(file.toPath(), TAGS);
+
+		try (final PdbReader reader = new PdbReader(pdbFile, false)) {
+
+			long value = 0;
+			int nextByte;
+			while ((nextByte = reader.readNextByte()) >= 0) {
+
+				final ByteType type = ByteType.getType(nextByte);
+				final long bytesValue = type.getValue(nextByte);
+
+				if (type == ByteType.CONTINUATION) {
+					value = value << ByteType.ContinuationByte.NUMBER_OF_VALUES_BITS;
+					value = value | type.getValue(nextByte);
+				} else {
+					value = bytesValue;
+				}
+
+				System.out.printf("%s %3d %3d %-14s %14d\n", toBinary(nextByte), nextByte, bytesValue, type, value);
+			}
+
+		}
+	}
+
+	private static String toBinary(final int b) {
+		return String.format("%8s", Integer.toBinaryString(b)).replace(" ", "0");
+	}
+
+}

performanceDb/src/main/java/org/lucares/performance/db/PdbReader.java

@@ -28,6 +28,10 @@ class PdbReader implements AutoCloseable {
 	private final PdbFile pdbFile;
 
 	public PdbReader(final PdbFile pdbFile) throws ReadException {
+		this(pdbFile, true);
+	}
+
+	PdbReader(final PdbFile pdbFile, final boolean initialize) throws ReadException {
 		super();
 		try {
 			this.pdbFile = pdbFile;
@@ -35,11 +39,12 @@ class PdbReader implements AutoCloseable {
 
 			this.data = new BufferedInputStream(new FileInputStream(storageFile));
 
+			if (initialize) {
 				init();
+			}
 		} catch (final FileNotFoundException e) {
 			throw new ReadException(e);
 		}
-
 	}
 
 	private void init() {
@@ -138,7 +143,7 @@ class PdbReader implements AutoCloseable {
 		return readContinuationBytes(value);
 	}
 
-	private int readNextByte() throws IOException {
+	int readNextByte() throws IOException {
 
 		final int result;
 		if (peekedByte == PEEK_NOT_SET) {
@@ -151,7 +156,7 @@ class PdbReader implements AutoCloseable {
 		return result;
 	}
 
-	private int peekNextByte() throws IOException {
+	int peekNextByte() throws IOException {
 		if (peekedByte == PEEK_NOT_SET) {
 			peekedByte = data.read();
 		}
@@ -160,7 +165,7 @@ class PdbReader implements AutoCloseable {
 
 	private long readContinuationBytes(long value) throws IOException {
 		int nextByte;
-		while ((nextByte = peekNextByte()) >= 0 && isContinuationByte(nextByte)) {
+		while ((nextByte = peekNextByte()) >= 0 && ByteType.CONTINUATION.isValid(nextByte)) {
 			value = value << ByteType.ContinuationByte.NUMBER_OF_VALUES_BITS;
 			value = value | (nextByte & ByteType.CONTINUATION.getValueBits());
 			readNextByte();
@@ -169,8 +174,4 @@ class PdbReader implements AutoCloseable {
 		return value;
 	}
 
-	private static boolean isContinuationByte(final int nextByte) {
-		final long bytePrefix = ByteType.CONTINUATION.getBytePrefix();
-		return bytePrefix == (nextByte & bytePrefix);
-	}
 }

performanceDb/src/main/java/org/lucares/performance/db/PdbWriter.java

@@ -40,8 +40,8 @@ import org.lucares.pdb.api.Entry;
  * <li>version, start with 000001
  * <li>number of entries up until this point in this file, 00001
  * <li>date offsets with absolute values for epoch milli, start with 0001
- * <li>date increments to the previous date value, start with 001
+ * <li>date increments to the previous date value, start with 01
- * <li>measurements, start with 01
+ * <li>measurements, start with 001
  * <li>continuation bytes, start with 1
  * </ol>
  *
@@ -60,12 +60,12 @@ import org.lucares.pdb.api.Entry;
  * used for the version number. 001 in our case. So the first byte looks like
  * this. 00001001
  * <p>
- * The second byte starts with 0001 for date offsets, 001 for date increments
+ * The second byte starts with 0001 for date offsets, 01 for date increments and
- * and 01 for measurements. All continuation bytes start with 1. E.g. The
+ * 001 for measurements. All continuation bytes start with 1. E.g. The
  * measurement 202 has the unsigned bit representation 11001010. The first byte
- * of a measurement value starts with 01, so we have room for the first 6 bits.
+ * of a measurement value starts with 001, so we have room for the first 5 bits.
  * But we need 8 bits. So we must add another byte. The second byte starts with
- * 1 and has room for 7 bits. The result looks like this: <b>01</b><i>000001<i>
+ * 1 and has room for 7 bits. The result looks like this: <b>001</b><i>00001<i>
  * <b>1</b><i>1001010</i>
  */
 class PdbWriter implements AutoCloseable, Flushable {