A hash function is any algorithm that maps data of arbitrary length to data of a fixed length. The values returned by a hash function are called hash values, hash codes, hash sums, checksums or simply hashes. From Wikipedia: http://en.wikipedia.org/wiki/Hash_function

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Linear probing hashing collision resolution

So I have a quick question about the linear probing method of collision resolution in hash tables. So by definition a linear probing method would look like: while (hashTable[hash] != null) hash = ...
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Max number of items mapped to same location in hashmap

I have a question about hashmaps. If you have this hashmap with m slots, and need to map n items to it, and n > m. There will be collisions for sure. But assuming there is simple uniform hashing ...
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Would md5 hashes allow detection of synced files?

We have to develop our own file management system in Java web application. We need to sync files between our main server and client severs and find out whether all the client server has all the latest ...
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How can “hash functions” be used to implement hash maps at all?

My understandment is that hash maps allow us to link, say, a string, to certain memory location. But if every string were to be linked to a unique place in memory it would need a huge block of empty ...
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How do scalable bloom filters work?

I was reading up on scalable bloom filters and could not understand how each time a constituent bloom filters fills up, a new bloom filter with larger size is added. The elements that contributed to ...
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Hash function classification

On the internet, I've come across this question: Classify the Hashing Functions based on the various methods by which the key value is found. with answers like Direct method Subtraction method ...
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Concept behind SHA-1 Checksum

What's the basis behind SHA-1 or SHA-2 or other Checksum algorithms? I read about it here http://en.wikipedia.org/wiki/SHA-1#Data_Integrity But I am still wondering about an answer in a layman's ...
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How to test if a hashing algorithm is good? [duplicate]

Possible Duplicate: Which hashing algorithm is best for uniqueness and speed? I have created a hash algorithm and would like to test if it is usable. What do I need to test and how?
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Basic memcached question

I have been reading up on distributed hashing. I learnt that consistent hashing is used for distributing the keys among cache machines. I also learnt that, a key is duplicated on mutiple caches to ...
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710 views

Hash Algorithm Randomness Visualization

I'm curious if anyone here has any idea how the images were generated as shown in this response: Which hashing algorithm is best for uniqueness and speed? Ian posted a very well-received response but ...
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2answers
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Looking for a non-cryptographic hash function that returns a single character

Suppose I have a dictionary of ASCII words stored in uppercase. I also want to save those words into separate files so that the total word count of each file is approximately the same. By simply ...
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History of Associative Array?

In quite a lot of modern scripting languages (e.g. Perl, Python, Ruby, PHP, Lua, JavaScript), associative arrays are supported as a primitive or first-class data type (with various names like map, ...
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Directory structure (file system design)

I was looking at how file systems are designed and noticed that most places say that the directory hierarchy can be implemented using a hash table. Could someone please explain me how using a hash ...
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Built-in Context-and-Input-to-Output-Hashing in Compilers

Why doesn't (open source) compilers contain builtin funtionality for (shared) caching and reuse-fetching (using SHA1-hash of compiler-version, build-flags, target-platform and inputs) of executable ...
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hash with file instead of array

Is it possible to use hash function but with File instead of Array, and it's gonna be saving the record in a file position and then search will fseek to that position, but I'm not sure how to open a ...
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Using account (login) password in generated PDF?

Ever since I heard about programming, I was told that any password (especially the one used on login) should be stored in database using any kind of one-way hashing algorithm, and never ever as plain ...
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Writing-Reading a hashtable to a text file

I'm implementing a hashtable structure for a dictionary. Dictionary is in a text file. There are 2 words on each line. I'm generating the hashtable by using the first word as a key. I'm holding the ...
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6answers
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What makes a hashing algorithm “secure”?

After reading this interesting question, I felt like I had a good idea of which insecure hashing algorithm I'd use if I needed one, but no idea why I might use a secure algorithm instead. So what is ...
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8answers
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Using HashTable without overriding hashcode()

Today I was asked this question during an interview: What will happen if we do not override the hashcode method for our class, then add it to HashTable and then try to get objects? What could ...
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How does a web browser save passwords?

How do current web browsers (or mobile mail clients and any software in general) save user passwords? All answers about storing passwords say we should store only hashes, not the password themselves. ...
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What are some common examples of a Hash Table? [closed]

I was just wondering if there were some "standard" examples that everyone uses as a basis for explaining the nature of a problem that requires the use of a Hash table. What are some well-known ...
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Is it more secure to hash a password multiple times?

I've read a few times that when storing passwords, it's good practice to 'double hash' the strings (eg. with md5 then sha1, both with salts, obviously). I guess the first question is, "is this ...
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1answer
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How costly are the Python dict and set in-built types?

I have undertaken a project concerning database deduplication. I did some research and have found that the Python dict type actually is a hashmap that uses open addressing. In the deduplication ...
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One global HashMap vs. many local HashMaps?

Which is more efficient; which is faster? Trade-offs? Goal is for fast look-ups in a web application. UUIDs are the keys, so global will work. Approx 50 million values. A global cache is ...
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Convert filenames to their checksum before saving to prevent duplicates. Is is a smart thing to do?

TL;DR:what the title says I am developing some sort of image board in PHP. I was thinking of changing each image's filename to it's checksum prior to saving it. This way, I might be able to ...
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7answers
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How do i speedily traverse a file system while extracting/extrapolating various data and provide user feedback?

I'm working on a system file scanner that reveals info about various files (e.g. size, last used, duplicates, etc). Currently I'm traversing the file system once just to get a good measure of the ...
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Is it possible to insert the hash of an executable into the executable itself without changing the resulting hash? What's the best alternative?

I've been thinking about this problem recently and it really doesn't seem like it's possible, but I figured that I'd ask just in case. Assume a simple program, in pseudocode: run hash on an ...
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Why almost no webpages hash passwords in the client before submitting (and hashing them again on the server), as to “protect” against password reuse?

Relevant XKCD There are many sites on the Internet that require login information, and the only way to protect against password reusing is the "promise" that the passwords are hashed on the server, ...
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3answers
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I'm trying to understand hash tables - can someone explain it to me - clearly?

I want to understand the correct use and implementation of hash tables in php (sorry). I read somewhere that an in-experienced programmer created a hash table and then iterated through it. Now, I ...
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6answers
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Where should salt hash values come from?

When adding salt values to a hash value for something like a password that cannot be stored in plain text, what is the best place to get the salt values come from? For context, let us suppose this is ...
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9answers
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Which hashing algorithm is best for uniqueness and speed?

Which hashing algorithm is best for uniqueness and speed? Example (good) uses include hash dictionaries. I know there are things like SHA-256 and such, but these algorithms are designed to be ...
6
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3answers
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Hashing growth strategy

What is a good growth strategy for hash tables? If the number of elements exceeds the number of buckets, I increase the number of buckets with the following formula: n = int(n * 1.618033988749895) | ...