Author: bodewig
Date: Thu May 3 16:07:38 2012
New Revision: 1333522
URL: http://svn.apache.org/viewvc?rev=1333522&view=rev
Log:
Add a few comments as earmarks for myself, I think this is what the code does.
Two 'final's thrown in for good measure
Modified:
commons/proper/compress/trunk/src/main/java/org/apache/commons/compress/compressors/bzip2/BZip2CompressorOutputStream.java
commons/proper/compress/trunk/src/main/java/org/apache/commons/compress/compressors/bzip2/BlockSort.java
Modified:
commons/proper/compress/trunk/src/main/java/org/apache/commons/compress/compressors/bzip2/BZip2CompressorOutputStream.java
URL:
http://svn.apache.org/viewvc/commons/proper/compress/trunk/src/main/java/org/apache/commons/compress/compressors/bzip2/BZip2CompressorOutputStream.java?rev=1333522&r1=1333521&r2=1333522&view=diff
==============================================================================
---
commons/proper/compress/trunk/src/main/java/org/apache/commons/compress/compressors/bzip2/BZip2CompressorOutputStream.java
(original)
+++
commons/proper/compress/trunk/src/main/java/org/apache/commons/compress/compressors/bzip2/BZip2CompressorOutputStream.java
Thu May 3 16:07:38 2012
@@ -315,7 +315,7 @@ public class BZip2CompressorOutputStream
private int blockCRC;
private int combinedCRC;
- private int allowableBlockSize;
+ private final int allowableBlockSize;
/**
* All memory intensive stuff.
@@ -391,6 +391,8 @@ public class BZip2CompressorOutputStream
}
this.blockSize100k = blockSize;
+ /* 20 is just a paranoia constant */
+ this.allowableBlockSize = (this.blockSize100k *
BZip2Constants.BASEBLOCKSIZE) - 20;
this.out = out;
init();
}
@@ -405,6 +407,19 @@ public class BZip2CompressorOutputStream
}
}
+ /**
+ * Writes the current byte to the buffer, run-length encoding it
+ * if it has been repeated at least four times (the first step
+ * RLEs sequences of four identical bytes).
+ *
+ * <p>Flushes the current block before writing data if it is
+ * full.</p>
+ *
+ * <p>"write to the buffer" means adding to data.buffer starting
+ * two steps "after" this.last - initially starting at index 1
+ * (not 0) - and updating this.last to point to the last index
+ * written minus 1.</p>
+ */
private void writeRun() throws IOException {
final int lastShadow = this.last;
@@ -534,9 +549,6 @@ public class BZip2CompressorOutputStream
for (int i = 256; --i >= 0;) {
inUse[i] = false;
}
-
- /* 20 is just a paranoia constant */
- this.allowableBlockSize = (this.blockSize100k *
BZip2Constants.BASEBLOCKSIZE) - 20;
}
private void endBlock() throws IOException {
@@ -632,6 +644,10 @@ public class BZip2CompressorOutputStream
}
}
+ /**
+ * Keeps track of the last bytes written and implicitly performs
+ * run-length encoding as the first step of the bzip2 algorithm.
+ */
private void write0(int b) throws IOException {
if (this.currentChar != -1) {
b &= 0xff;
@@ -1153,6 +1169,13 @@ public class BZip2CompressorOutputStream
return blockSorter.blockSort(data, last);
}
+ /*
+ * Performs Move-To-Front on the Burrows-Wheeler transformed
+ * buffer, storing the MTFed data in data.sfmap in RUNA/RUNB
+ * run-length-encoded form.
+ *
+ * <p>Keeps track of byte frequencies in data.mtfFreq at the same time.</p>
+ */
private void generateMTFValues() {
final int lastShadow = this.last;
final Data dataShadow = this.data;
@@ -1259,6 +1282,7 @@ public class BZip2CompressorOutputStream
static final class Data extends Object {
// with blockSize 900k
+ /* maps unsigned byte => "does it occur in block" */
final boolean[] inUse = new boolean[256]; // 256 byte
final byte[] unseqToSeq = new byte[256]; // 256 byte
final int[] mtfFreq = new int[MAX_ALPHA_SIZE]; // 1032 byte
@@ -1284,7 +1308,12 @@ public class BZip2CompressorOutputStream
// ------------
// 333408 byte
+ /* holds the RLEd block of original data starting at index 1.
+ * After sorting the last byte added to the buffer is at index
+ * 0. */
final byte[] block; // 900021 byte
+ /* maps index in Burrows-Wheeler transformed block => index of
+ * byte in original block */
final int[] fmap; // 3600000 byte
final char[] sfmap; // 3600000 byte
// ------------
Modified:
commons/proper/compress/trunk/src/main/java/org/apache/commons/compress/compressors/bzip2/BlockSort.java
URL:
http://svn.apache.org/viewvc/commons/proper/compress/trunk/src/main/java/org/apache/commons/compress/compressors/bzip2/BlockSort.java?rev=1333522&r1=1333521&r2=1333522&view=diff
==============================================================================
---
commons/proper/compress/trunk/src/main/java/org/apache/commons/compress/compressors/bzip2/BlockSort.java
(original)
+++
commons/proper/compress/trunk/src/main/java/org/apache/commons/compress/compressors/bzip2/BlockSort.java
Thu May 3 16:07:38 2012
@@ -19,7 +19,8 @@
package org.apache.commons.compress.compressors.bzip2;
/**
- * Encapsulates the sorting algorithms needed by {@link
BZip2CompressorOutputStream}.
+ * Encapsulates the Burrows-Wheeler sorting algorithm needed by {@link
+ * BZip2CompressorOutputStream}.
*
* @NotThreadSafe
*/
@@ -301,7 +302,7 @@ class BlockSort {
mainSort(data, last);
}
- int[] fmap = data.fmap;
+ final int[] fmap = data.fmap;
data.origPtr = -1;
for (int i = 0; i <= last; i++) {
if (fmap[i] == 0) {
