Uint128_64

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struct Uint128_64  
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struct Uint128_64

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Copyright (c) 2011 Google, Inc.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

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CityHash, by Geoff Pike and Jyrki Alakuijala

http://code.google.com/p/cityhash/

This file provides a few functions for hashing strings. All of them are high-quality functions in the sense that they pass standard tests such as Austin Appleby's SMHasher. They are also fast.

For 64-bit x86 code, on short strings, we don't know of anything faster than CityHash64 that is of comparable quality. We believe our nearest competitor is Murmur3. For 64-bit x86 code, CityHash64 is an excellent choice for hash tables and most other hashing (excluding cryptography).

For 64-bit x86 code, on long strings, the picture is more complicated. On many recent Intel CPUs, such as Nehalem, Westmere, Sandy Bridge, etc., CityHashCrc128 appears to be faster than all competitors of comparable quality. CityHash128 is also good but not quite as fast. We believe our nearest competitor is Bob Jenkins' Spooky. We don't have great data for other 64-bit CPUs, but for long strings we know that Spooky is slightly faster than CityHash on some relatively recent AMD x86-64 CPUs, for example. Note that CityHashCrc128 is declared in citycrc.h.

For 32-bit x86 code, we don't know of anything faster than CityHash32 that is of comparable quality. We believe our nearest competitor is Murmur3A. (On 64-bit CPUs, it is typically faster to use the other CityHash variants.)

Functions in the CityHash family are not suitable for cryptography.

Please see CityHash's README file for more details on our performance measurements and so on.

WARNING: This code has been only lightly tested on big-endian platforms! It is known to work well on little-endian platforms that have a small penalty for unaligned reads, such as current Intel and AMD moderate-to-high-end CPUs. It should work on all 32-bit and 64-bit platforms that allow unaligned reads; bug reports are welcome.

By the way, for some hash functions, given strings a and b, the hash of a+b is easily derived from the hashes of a and b. This property doesn't hold for any hash functions in this file.

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