/prog/ - hashing algorithm

Name: hasher 2009-06-22 12:14

Hello, I need an hashing algorithm which outputs a hash which doesn't change much if the output doesn't change much.
Ideally if I had string1 which were quite similar to string2, the two hashes should differ by something comparable to the Levenshtein distance.
That's not really important though.
I thought about an homothetic transformation (that is taking each nth character in order to end up with a constant length string), but I don't really know.
Any suggestions?

Name: Anonymous 2009-06-22 12:38

I lol'd

Name: Anonymous 2009-06-22 12:46

First in Google search using the keywords hash similar algorithm.
http://en.wikipedia.org/wiki/Hash_function#Finding_similar_records

Name: hasher 2009-06-22 13:17

@3
I already read that, but I don't think music brainz acoustic fingerprint algorithm is right for text strings...

Name: hasher 2009-06-22 13:19

also @3, I expected a little bit more than a &STARTSQUOTE;wikipedia article&ENDSQUOTE;

Name: !!OLEWaicmZnzzZYR 2009-06-22 13:25

a

Name: test 2009-06-22 13:46

>>6
lol wat?

Name: Anonymous 2009-06-22 13:57

TRY THE IDENTITY FUNCTION.

Name: Anonymous 2009-06-22 14:15

>>3,4
How about you learn how this board works before you post again?

Name: hasher 2009-06-22 14:46

@8
I need constant length.

Name: Anonymous 2009-06-22 14:47

@9
you mean the useless threads on SICP or on the favourite programming language?

Name: Anonymous 2009-06-22 14:57

>>11
a9
back to /twitter/ please

Name: Anonymous 2009-06-22 14:57

s/a9/@9/

Name: Anonymous 2009-06-22 16:01

>>13
s/\@/\\\@/

Name: Anonymous 2009-06-22 17:04

>>14
s/\\/\\\\/

Name: Anonymous 2009-06-22 17:23

>>15
s/\\\\/\\\\\\\\/

Name: Anonymous 2009-06-22 19:39

>>1
homothetic transformation
I read that as homoerotic.

Also, phash.

Name: Anonymous 2009-06-22 20:28

>>17
Hi Xarn, a little disappointed are we?

Name: Anonymous 2009-06-23 8:17

>>18
have you tried not being a butt-munch?

Name: Anonymous 2009-06-23 10:56

>>18
What?
I'm not Xarn.

Name: Anonymous 2009-06-23 11:35

969ee999438c2d4d4de5 - How about you learn how this board works before you post again? 829ee999438c2d4d49e5 - How about you learn how this board works before uoa post again? d5bed6b9a9ed94b4bc59 - How about you learn how this board works before you post again, faggot? 969ee999438c2d514de5 - How about you learn how this board works before you post egain? 590d9e715e46b09ec9ed - Wow, about time you learn how this board works before you post again! 590d9e715e46b09ee7ed - Wow, about time you learn how this board works before you post again? bf6e05d8cdbaef9ed40d - Wow, about time you learn how this board works before you post again, faggot? bf6e05d8cdbad1ddd40d - Wow, about time you learn how this board works before you post again, faggot!?

Name: Anonymous 2009-06-23 15:21



fioc

fico

foic

foci

fcio

fcoi

ifoc

ifco

iofc

iocf

icfo

icof

ofic

ofci

oifc

oicf

ocfi

ocif

cfio

cfoi

cifo

ciof

cofi

coif

Name: Anonymous 2009-06-23 15:34

Tell me how this works:



module WhatHash where



import Char

import Numeric



{-

The [i]homoerotic[/i] hashing algorithm requested in http://dis.4chan.org/read/prog/1245687289

-}



data Binary = Binary [Bool] deriving Eq



xor True = not

xor False = id



pow2s = map (2^) [0..]



intToBin 0 = []

intToBin x = reverse $ que (-1) what

         where que l (y:ys) | y == 0    = False:que y ys

                            | y == x    = [True]

                            | y == l    = False:que y ys

                            | otherwise = True:que y ys

               what = map (mod x) $ tail pow2s



binToInt xs' = binToInt' 0

          where xs = reverse xs'

                binToInt' n | n >= length xs = 0

                            | xs !! n        = (pow2s !! n) + binToInt' (n+1)

                            | otherwise      = binToInt' (n+1)



padl n p list | length list >= n = list

              | otherwise        = padl n p (p:list)



charToByte = padl 8 False . intToBin . ord

byteToChar = chr . binToInt



instance Show Binary where

    show (Binary [])         = ""

    show (Binary (True:xs))  = '1':show (Binary xs)

    show (Binary (False:xs)) = '0':show (Binary xs)



instance Read Binary where

    readsPrec _ xs = [(Binary $ map q xs,"")]

          where q '1' = True

                q _   = False



splitEvery n xs | length next > 0 = this:splitEvery n next

                | otherwise       = [this]

              where (this,next) = splitAt n xs



--(accumulate-n) from SICP Exercise 2.36

foldrn f n []     = []

foldrn f n ([]:_) = []

foldrn f n xs     = foldr f n (q head xs):foldrn f n (q tail xs)

    where q ad = map ad . filter (/=[])



whatHash = foldrn xor True . splitEvery 128



hashStrToBin = whatHash . concatMap charToByte . padl 16 ' '



hashStrToBytes = map byteToChar . splitEvery 8 . hashStrToBin



hashStrToStr = foldr showHex "" . map binToInt . splitEvery 8 . hashStrToBin

Name: Anonymous 2009-06-23 15:46

>>23
magic

Name: Anonymous 2009-06-23 18:12

>>23
Let me clarify: Tell me how well this works for your purpose, >>1.

Name: Anonymous 2013-04-22 22:27

aye

Name: Anonymous 2013-04-23 13:54





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hashing algorithm

1 Name: hasher 2009-06-22 12:14

2 Name: Anonymous 2009-06-22 12:38

3 Name: Anonymous 2009-06-22 12:46

4 Name: hasher 2009-06-22 13:17

5 Name: hasher 2009-06-22 13:19

6 Name: !!OLEWaicmZnzzZYR 2009-06-22 13:25

7 Name: test 2009-06-22 13:46

8 Name: Anonymous 2009-06-22 13:57

9 Name: Anonymous 2009-06-22 14:15

10 Name: hasher 2009-06-22 14:46

11 Name: Anonymous 2009-06-22 14:47

12 Name: Anonymous 2009-06-22 14:57

13 Name: Anonymous 2009-06-22 14:57

14 Name: Anonymous 2009-06-22 16:01

15 Name: Anonymous 2009-06-22 17:04

16 Name: Anonymous 2009-06-22 17:23

17 Name: Anonymous 2009-06-22 19:39

18 Name: Anonymous 2009-06-22 20:28

19 Name: Anonymous 2009-06-23 8:17

20 Name: Anonymous 2009-06-23 10:56

21 Name: Anonymous 2009-06-23 11:35

22 Name: Anonymous 2009-06-23 15:21

23 Name: Anonymous 2009-06-23 15:34

24 Name: Anonymous 2009-06-23 15:46

25 Name: Anonymous 2009-06-23 18:12

27 Name: Anonymous 2013-04-22 22:27

28 Name: Anonymous 2013-04-23 13:54

29 Name: Anonymous 2013-04-23 14:05

30 Name: Anonymous 2013-04-23 14:13

31 Name: Anonymous 2013-04-23 14:28

32 Name: Anonymous 2013-04-23 14:40

33 Name: Anonymous 2013-04-24 0:22

34 Name: Anonymous 2013-04-24 0:30

35 Name: Anonymous 2013-04-24 0:35

36 Name: Anonymous 2013-04-24 0:42

37 Name: Anonymous 2013-04-24 0:53

38 Name: Anonymous 2013-04-24 0:59

39 Name: Anonymous 2013-04-24 1:05

Name: hasher 2009-06-22 12:14

Name: Anonymous 2009-06-22 12:38

Name: Anonymous 2009-06-22 12:46

Name: hasher 2009-06-22 13:17

Name: hasher 2009-06-22 13:19

Name: !!OLEWaicmZnzzZYR 2009-06-22 13:25

Name: test 2009-06-22 13:46

Name: Anonymous 2009-06-22 13:57

Name: Anonymous 2009-06-22 14:15

Name: hasher 2009-06-22 14:46

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Name: Anonymous 2009-06-23 11:35

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Name: Anonymous 2009-06-23 15:34

Name: Anonymous 2009-06-23 15:46

Name: Anonymous 2009-06-23 18:12

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