[Haskell-cafe] compressed pointers?

Don Stewart dons at galois.com
Wed Apr 16 10:59:34 EDT 2008

> One of the downsides of a 64-bit environment is the increased size of
> pointers.  This means that the cost of a String increases from
> something like 12 bytes per char to something like 24.
> I notice BEA uses something called "compressed pointers" to get the
> 64-bit (more registers, etc) benefits without paying the
> (cache-thrashing) cost.
>   http://e-docs.bea.com/jrockit/releases/5026x/relnotes/relnotes.html#wp1079760
> Something for GHC?

One small upside (performance wise), is that the bottom 3 bits of the
pointer are now used to encode the constructor on 64 bits, so 'case' gets a
good percent cheaper.

-- Don

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