Package org.eclipse.jgit.pgm.debug

Class TextHashFunctions

java.lang.Object

org.eclipse.jgit.pgm.TextBuiltin

org.eclipse.jgit.pgm.debug.TextHashFunctions

class TextHashFunctions
extends TextBuiltin

Scan repository to compute maximum number of collisions for hash functions. This is a test suite to help benchmark the collision rate of hash functions when applied to file contents in a Git repository. The test scans all text files in the HEAD revision of the repository it is run within. For each file it finds the unique lines, and then inserts those lines into a hash table to determine collision rates under the selected hash functions. To add another hash function to the test suite, declare a new instance member field of type TextHashFunctions.Hash and implement the hashRegion method. The test suite will automatically pick up the new function through reflection. To add another folding function (method of squashing a 32 bit hash code into the hash tables smaller array index space), declare a new instance field of type TextHashFunctions.Fold and implement the logic. The test suite will automatically pick up the new function through reflection.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
private static class	TextHashFunctions.Fold	Base class for any hashCode folding function to be tested.
private static class	TextHashFunctions.Function
private static class	TextHashFunctions.Hash	Base class for any hashCode function to be tested.
private static class	TextHashFunctions.Line	Utility to help us identify unique lines in a file.

Nested classes/interfaces inherited from class org.eclipse.jgit.pgm.TextBuiltin

TextBuiltin.TerminatedByHelpException

Field Summary

Fields

Modifier and Type	Field	Description
(package private) TextHashFunctions.Hash	djb	Professor Daniel J.
(package private) java.util.List<java.lang.String>	foldFunctions
(package private) java.util.List<java.io.File>	gitDirs
(package private) TextHashFunctions.Fold	golden_ratio	Applies the golden ratio and takes the upper bits.
(package private) java.util.List<java.lang.String>	hashFunctions
(package private) TextHashFunctions.Hash	rabin_DeltaIndex	The Rabin polynomial hash that is used by our own DeltaIndex.
(package private) TextHashFunctions.Hash	sha1	Standard SHA-1 on the line, using the first 4 bytes as the hash code.
(package private) TextHashFunctions.Hash	string_hash31	Hash function commonly used by java.lang.String.
(package private) int	textLimit
(package private) TextHashFunctions.Fold	truncate	Bitwise-and to extract only the low bits.

Fields inherited from class org.eclipse.jgit.pgm.TextBuiltin

argWalk, db, errs, errw, gitdir, ins, outs, outw

Constructor Summary

Constructors

Constructor	Description
TextHashFunctions()

Method Summary

Modifier and Type	Method	Description
private static boolean	include(java.lang.String name, java.util.List<java.lang.String> want)
private java.util.List<TextHashFunctions.Function>	init()
protected boolean	requiresRepository()	If this command requires a repository.
protected void	run()	Perform the actions of this command.
private void	run(Repository repo)
private static int	tableBits(int sz)
private static void	testOne(TextHashFunctions.Function fun, RawText txt, int[] elements, int cnt)

Methods inherited from class org.eclipse.jgit.pgm.TextBuiltin

containsHelp, die, die, die, die, execute, getErrorWriter, getOutputWriter, getRepository, getResourceBundle, init, initRaw, parseArguments, printUsage, printUsageAndExit, printUsageAndExit

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

sha1

final TextHashFunctions.Hash sha1

Standard SHA-1 on the line, using the first 4 bytes as the hash code.

djb

final TextHashFunctions.Hash djb

Professor Daniel J. Bernstein's rather popular string hash.

string_hash31

final TextHashFunctions.Hash string_hash31

Hash function commonly used by java.lang.String.

rabin_DeltaIndex

final TextHashFunctions.Hash rabin_DeltaIndex

The Rabin polynomial hash that is used by our own DeltaIndex.

truncate

final TextHashFunctions.Fold truncate

Bitwise-and to extract only the low bits.

golden_ratio

final TextHashFunctions.Fold golden_ratio

Applies the golden ratio and takes the upper bits.

hashFunctions

java.util.List<java.lang.String> hashFunctions

foldFunctions

java.util.List<java.lang.String> foldFunctions

textLimit

int textLimit

gitDirs

java.util.List<java.io.File> gitDirs

Constructor Detail

TextHashFunctions

TextHashFunctions()

Method Detail

requiresRepository

protected boolean requiresRepository()

If this command requires a repository.

Overrides:

requiresRepository in class TextBuiltin

Returns:

true if TextBuiltin.db/TextBuiltin.getRepository() is required

run

protected void run()
            throws java.lang.Exception

Perform the actions of this command.

This method should only be invoked by TextBuiltin.execute(String[]).

Specified by:

run in class TextBuiltin

Throws:

java.lang.Exception - an error occurred while processing the command. The main framework will catch the exception and print a message on standard error.

run

private void run(Repository repo)
          throws java.lang.Exception

Throws:

java.lang.Exception

testOne

private static void testOne(TextHashFunctions.Function fun,
                            RawText txt,
                            int[] elements,
                            int cnt)

init

private java.util.List<TextHashFunctions.Function> init()

include

private static boolean include(java.lang.String name,
                               java.util.List<java.lang.String> want)

tableBits

private static int tableBits(int sz)