Class BlockSort
BZip2CompressorOutputStream
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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:
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Field Summary
FieldsModifier and TypeFieldDescriptionprivate static final int
private static final int
private int[]
private static final int
private static final int
private boolean
private final int[]
private static final int[]
private final boolean[]
private final int[]
private final int[]
private static final int
private final char[]
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 final int
private static final int
private final int[]
private final int[]
private final int[]
private static final int
private static final int
private int
private int
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescription(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) final void
fallbackSort
(int[] fmap, byte[] block, int nblock) (package private) final 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).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 fmapprivate 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[]
private void
mainQSort3
(BZip2CompressorOutputStream.Data dataShadow, int loSt, int hiSt, int dSt, int last) Method "mainQSort3", file "blocksort.c", BZip2 1.0.2private boolean
mainSimpleSort
(BZip2CompressorOutputStream.Data dataShadow, int lo, int hi, int d, int lastShadow) This is the most hammered method of this class.(package private) final 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)
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Field Details
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QSORT_STACK_SIZE
private static final int QSORT_STACK_SIZE- See Also:
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FALLBACK_QSORT_STACK_SIZE
private static final int FALLBACK_QSORT_STACK_SIZE- See Also:
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STACK_SIZE
private static final int STACK_SIZE- See Also:
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workDone
private int workDone -
workLimit
private int workLimit -
firstAttempt
private boolean firstAttempt -
stack_ll
private final int[] stack_ll -
stack_hh
private final int[] stack_hh -
stack_dd
private final int[] stack_dd -
mainSort_runningOrder
private final int[] mainSort_runningOrder -
mainSort_copy
private final int[] mainSort_copy -
mainSort_bigDone
private final boolean[] mainSort_bigDone -
ftab
private final int[] ftab -
quadrant
private final char[] quadrantArray instance identical to Data's sfmap, both are used only temporarily and indepently, so we do not need to allocate additional memory. -
FALLBACK_QSORT_SMALL_THRESH
private static final int FALLBACK_QSORT_SMALL_THRESH- See Also:
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eclass
private int[] eclass -
INCS
private static final int[] INCS -
SMALL_THRESH
private static final int SMALL_THRESH- See Also:
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DEPTH_THRESH
private static final int DEPTH_THRESH- See Also:
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WORK_FACTOR
private static final int WORK_FACTOR- See Also:
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SETMASK
private static final int SETMASK- See Also:
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CLEARMASK
private static final int CLEARMASK- See Also:
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Constructor Details
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BlockSort
BlockSort(BZip2CompressorOutputStream.Data data)
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Method Details
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blockSort
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fallbackSort
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). -
fallbackSimpleSort
private void fallbackSimpleSort(int[] fmap, int[] eclass, int lo, int hi) - Parameters:
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 sorted
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fswap
private void fswap(int[] fmap, int zz1, int zz2) swaps two values in fmap -
fvswap
private void fvswap(int[] fmap, int yyp1, int yyp2, int yyn) swaps two intervals starting at yyp1 and yyp2 of length yyn inside fmap. -
fmin
private int fmin(int a, int b) -
fpush
private void fpush(int sp, int lz, int hz) -
fpop
private int[] fpop(int sp) -
fallbackQSort3
private void fallbackQSort3(int[] fmap, int[] eclass, int loSt, int hiSt) - Parameters:
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 sorted
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getEclass
private int[] getEclass() -
fallbackSort
final void fallbackSort(int[] fmap, byte[] block, int nblock) - Parameters:
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 block
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mainSimpleSort
private boolean mainSimpleSort(BZip2CompressorOutputStream.Data dataShadow, int lo, int hi, int d, int lastShadow) This is the most hammered method of this class.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.
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vswap
private static void vswap(int[] fmap, int p1, int p2, int n) -
med3
private static byte med3(byte a, byte b, byte c) -
mainQSort3
private void mainQSort3(BZip2CompressorOutputStream.Data dataShadow, int loSt, int hiSt, int dSt, int last) Method "mainQSort3", file "blocksort.c", BZip2 1.0.2 -
mainSort
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