Bitstate hashing

Bitstate hashing is a hashing method invented in 1968 by Morris.[1] It is used for state hashing, where each state (e.g. of an automaton) is represented by a number and it is passed to some hash function.

The result of the function is then taken as the index to an array of bits (a bit-field), where one looks for 1 if the state was already seen before or stores 1 by itself if not.

It usually serves as a yes–no technique without a need of storing whole state bit representation.

A shortcoming of this framework is losing precision like in other hashing techniques. Hence some tools use this technique with more than one hash function so that the bit-field gets widened by the number of used functions, each having its own row. And even after all functions return values (the indices) point to fields with contents equal to 1, the state may be uttered as visited with much higher probability.

Use

References

  1. Morris, R. (1968). Scatter Storage Techniques
  2. Holzmann, G. J. (2003) Addison Wesley. Spin Model Checker, The: Primer and Reference Manual
This article is issued from Wikipedia - version of the 12/16/2014. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.