[gambit-list] table-update! primitive

Marc Feeley feeley at iro.umontreal.ca
Sat Oct 26 17:07:37 EDT 2019


It is not just resizing, it could also have been rehashed, which can happen after a GC for eq? hash tables.  The conditions under which a single lookup is sufficient will have to be studied carefully in order to optimize that case.  So for now a double lookup seems like the easy path forward.

Marc



> On Oct 26, 2019, at 4:34 PM, Dimitris Vyzovitis <vyzo at hackzen.org> wrote:
> 
> Couldn't it check whether there has been resize in between and avoid the second lookup if there hasn't been one?
> 
> -- vyzo
> 
> On Sat, Oct 26, 2019 at 11:31 PM Marc Feeley <feeley at iro.umontreal.ca> wrote:
> I’m currently reimplementing tables, so it is a good time to consider this.
> 
> However, the “obvious” implementation which does one lookup will not work because the update procedure may cause the gc hash table to be resized.  So a lookup must be done before and after the update procedure is executed.  However it is possible to avoid repeating some type checks.
> 
> Marc
> 
> 
> 
> > On Oct 26, 2019, at 12:45 PM, Dimitris Vyzovitis <vyzo at hackzen.org> wrote:
> > 
> > Marc,
> > 
> > Can we add a table-update! primitive? 
> > Updates are currently slow because they need two lookups in the hash table, one to find the current value (if any) and one to set it.
> > The canonical signature is (table-update! table key update default), where update is applied to the current value, using default if the value is unset.
> > 
> > -- vyzo
> 
> 





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