[Mono-dev] String.GetHashCode()

Robert Jordan robertj at gmx.net
Sat Dec 1 12:29:50 EST 2007

Hi Alan,

Alan McGovern wrote:
> Also, just looking at the string source a bit more closely, it has a
> GetCaseInsensitiveHashcode method too, so i'd assume that would need to be
> cached too which would mean 8 bytes would be needed. This wouldn't scale
> well.
> Fair enough. Twas just an idea.

nah, don't give up too early! :) If the string is longer than "n",
you could allocate 4 or even 8 additional bytes at the end of the
array for lazily computed hash codes.

Open questions:

- What's the optimal "n" for all common application classes
   mono is used for? :) It looks like it should be dynamically
   computed & adjusted based on profiling data collected at

- What's the real gain of this optimization? If "n" tends to
   be really large (say 1-4KB), what's the probability of
   such large strings being used as a hash key?
   This question can be reduced to "how frequently is
   s.GetHashCode called, where s.Length > n".

   In mono's class libs sources there is only one place (I know
   of) where large strings are potentially hashed: Sys.Web's
   cache management.


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