hashing
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The Halton sequence can be used like a random number generator to produce points in the interval [0,1]. The Halton sequence is even less random than a random number generator; if you specify the index I of the Halton number you want, there is a formula for producing H(I). On the other hand, the Halton sequence does a better job of filling in the region, avoiding the large gaps that can occur with a random number generator. The idea is simple. We choose a base, let's say 2.
The Halton Sequence
Cuckoo hashing - Wikipedia, the free encyclopedia
Cuckoo hashing example. The arrows show the alternative location of each key. A new item would be inserted in the location of A by moving A to its alternative location, currently occupied by B, and moving B to its alternative location which is currently vacant. Insertion of a new item in the location of H would not succeed: Since H is part of a cycle (together with W), the new item would get kicked out again.
CMPH - C Minimal Perfect Hashing Library
Motivation A perfect hash function maps a static set of n keys into a set of m integer numbers without collisions, where m is greater than or equal to n. If m is equal to n, the function is called minimal.We get asked a lot about the colour-coding we give to places in Dopplr : what it represents, why we did it, how are the colours assigned. One of the main ‘atoms’ of Dopplr is unsurprisingly, place – so to make that run through the warp-and-weft of the user-interface, and our branding, was extremely important. The Dopplr logo, (or ‘SparkLogo’ * as we sometimes like to call it) is the clearest example of this perhaps. As you add trips to different destinations, Dopplr’s logo becomes your logo, reflecting what you’re doing – right the way through to the ‘ favicon ‘ that shows up in the address field of most browsers. It also makes for a great blog badge… As well as the aesthetic delights we believe that city colours bring to the service, we’re using them as visual ‘ affordances ‘ – ways to create implicit meaning and usefulness in the user-interface.
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Stop using unsafe keyed hashes, use HMAC « root labs rdist
The HMAC construction turns a cryptographic hash algorithm into a keyed hash. It is commonly used for integrity protection when the sender and recipient share a secret key. It was developed to address various problems with arbitrary keyed hash constructions. So why are developers still rolling their own? One of the original papers on keyed hash constructions describes the motivations for developing a standard for HMAC. In 1995, there was no standardization and cryptographers only worked from hunches as to what constituted a secure keyed hash.
MD5 and cryptographic hash functions in general have many uses - not least integrity checking and password storage. They have the property of mixing the input in an unpredictable but deterministic way. This can be very useful - and not just in security applications.
Tom White: Mixing with MD5
