class BlockSort
extends java.lang.Object
BZip2CompressorOutputStream
.
This class is based on a Java port of Julian Seward's blocksort.c in his libbzip2
The Burrows-Wheeler transform is a reversible transform of the original data that is supposed to group similar bytes close to each other. The idea is to sort all permutations of the input and only keep the last byte of each permutation. E.g. for "Commons Compress" you'd get:
CompressCommons Commons Compress CompressCommons essCommons Compr mmons CompressCo mons CompressCom mpressCommons Co ns CompressCommo ommons CompressC ompressCommons C ons CompressComm pressCommons Com ressCommons Comp s CompressCommon sCommons Compres ssCommons Compre
Which results in a new text "ss romooCCmmpnse", in adition the index of the first line that contained the original text is kept - in this case it is 1. The idea is that in a long English text all permutations that start with "he" are likely suffixes of a "the" and thus they end in "t" leading to a larger block of "t"s that can better be compressed by the subsequent Move-to-Front, run-length und Huffman encoding steps.
For more information see for example:
Modifier and Type | Field and Description |
---|---|
private static int |
CLEARMASK |
private static int |
DEPTH_THRESH |
private int[] |
eclass |
private static int |
FALLBACK_QSORT_SMALL_THRESH |
private static int |
FALLBACK_QSORT_STACK_SIZE |
private boolean |
firstAttempt |
private int[] |
ftab |
private static int[] |
INCS |
private boolean[] |
mainSort_bigDone |
private int[] |
mainSort_copy |
private int[] |
mainSort_runningOrder |
private static int |
QSORT_STACK_SIZE |
private char[] |
quadrant
Array instance identical to Data's sfmap, both are used only
temporarily and indepently, so we do not need to allocate
additional memory.
|
private static int |
SETMASK |
private static int |
SMALL_THRESH |
private int[] |
stack_dd |
private int[] |
stack_hh |
private int[] |
stack_ll |
private static int |
STACK_SIZE |
private static int |
WORK_FACTOR |
private int |
workDone |
private int |
workLimit |
Constructor and Description |
---|
BlockSort(BZip2CompressorOutputStream.Data data) |
Modifier and Type | Method and Description |
---|---|
(package private) void |
blockSort(BZip2CompressorOutputStream.Data data,
int last) |
private void |
fallbackQSort3(int[] fmap,
int[] eclass,
int loSt,
int hiSt) |
private void |
fallbackSimpleSort(int[] fmap,
int[] eclass,
int lo,
int hi) |
(package private) void |
fallbackSort(BZip2CompressorOutputStream.Data data,
int last)
Adapt fallbackSort to the expected interface of the rest of the
code, in particular deal with the fact that block starts at
offset 1 (in libbzip2 1.0.6 it starts at 0).
|
(package private) void |
fallbackSort(int[] fmap,
byte[] block,
int nblock) |
private int |
fmin(int a,
int b) |
private int[] |
fpop(int sp) |
private void |
fpush(int sp,
int lz,
int hz) |
private void |
fswap(int[] fmap,
int zz1,
int zz2)
swaps two values in fmap
|
private void |
fvswap(int[] fmap,
int yyp1,
int yyp2,
int yyn)
swaps two intervals starting at yyp1 and yyp2 of length yyn inside fmap.
|
private int[] |
getEclass() |
private void |
mainQSort3(BZip2CompressorOutputStream.Data dataShadow,
int loSt,
int hiSt,
int dSt,
int last)
Method "mainQSort3", file "blocksort.c", BZip2 1.0.2
|
private boolean |
mainSimpleSort(BZip2CompressorOutputStream.Data dataShadow,
int lo,
int hi,
int d,
int lastShadow)
This is the most hammered method of this class.
|
(package private) void |
mainSort(BZip2CompressorOutputStream.Data dataShadow,
int lastShadow) |
private static byte |
med3(byte a,
byte b,
byte c) |
private static void |
vswap(int[] fmap,
int p1,
int p2,
int n) |
private static final int QSORT_STACK_SIZE
private static final int FALLBACK_QSORT_STACK_SIZE
private static final int STACK_SIZE
private int workDone
private int workLimit
private boolean firstAttempt
private final int[] stack_ll
private final int[] stack_hh
private final int[] stack_dd
private final int[] mainSort_runningOrder
private final int[] mainSort_copy
private final boolean[] mainSort_bigDone
private final int[] ftab
private final char[] quadrant
private static final int FALLBACK_QSORT_SMALL_THRESH
private int[] eclass
private static final int[] INCS
private static final int SMALL_THRESH
private static final int DEPTH_THRESH
private static final int WORK_FACTOR
private static final int SETMASK
private static final int CLEARMASK
BlockSort(BZip2CompressorOutputStream.Data data)
void blockSort(BZip2CompressorOutputStream.Data data, int last)
final void fallbackSort(BZip2CompressorOutputStream.Data data, int last)
private void fallbackSimpleSort(int[] fmap, int[] eclass, int lo, int hi)
fmap
- points to the index of the starting point of a
permutation inside the block of data in the current
partially sorted ordereclass
- points from the index of a character inside the
block to the first index in fmap that contains the
bucket of its suffix that is sorted in this step.lo
- lower boundary of the fmap-interval to be sortedhi
- upper boundary of the fmap-interval to be sortedprivate void fswap(int[] fmap, int zz1, int zz2)
private void fvswap(int[] fmap, int yyp1, int yyp2, int yyn)
private int fmin(int a, int b)
private void fpush(int sp, int lz, int hz)
private int[] fpop(int sp)
private void fallbackQSort3(int[] fmap, int[] eclass, int loSt, int hiSt)
fmap
- points to the index of the starting point of a
permutation inside the block of data in the current
partially sorted ordereclass
- points from the index of a character inside the
block to the first index in fmap that contains the
bucket of its suffix that is sorted in this step.loSt
- lower boundary of the fmap-interval to be sortedhiSt
- upper boundary of the fmap-interval to be sortedprivate int[] getEclass()
final void fallbackSort(int[] fmap, byte[] block, int nblock)
fmap
- points to the index of the starting point of a
permutation inside the block of data in the current
partially sorted orderblock
- the original datanblock
- size of the blockoff
- offset of first byte to sort in blockprivate boolean mainSimpleSort(BZip2CompressorOutputStream.Data dataShadow, int lo, int hi, int d, int lastShadow)
This is the version using unrolled loops. Normally I never use such ones in Java code. The unrolling has shown a noticable performance improvement on JRE 1.4.2 (Linux i586 / HotSpot Client). Of course it depends on the JIT compiler of the vm.
private static void vswap(int[] fmap, int p1, int p2, int n)
private static byte med3(byte a, byte b, byte c)
private void mainQSort3(BZip2CompressorOutputStream.Data dataShadow, int loSt, int hiSt, int dSt, int last)
final void mainSort(BZip2CompressorOutputStream.Data dataShadow, int lastShadow)