[Mesa-dev] [PATCH] util: Change the pointer hashing function

[Eric Anholt]

Thomas Helland <thomashelland90 at gmail.com> writes:

> Use our knowledge that pointers are at least 4 byte aligned to remove
> the useless digits. Then shift by 6, 10, and 14 bits and add this to
> the original pointer, effectively folding in the entropy of the higher
> bits of the pointer into a 4-bit section. Stopping at 14 means we can
> add the entropy from 18 bits, or at least a 600Kbyte section of memory.
> Assuming that ralloc allocates from a linearly allocated heap less than
> this we can make a very efficient pointer hashing function for our usecase.

The fnv1 on the pointer was basically a stand-in until someone did the
kind of analysis you've done here.  Thanks!

Reviewed-by: Eric Anholt <eric at anholt.net>
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