Re: An approach for cheap small tables of int values

[Daurnimator <quae@...>]

On 11 March 2018 at 12:07, Dibyendu Majumdar <mobile@majumdar.org.uk> wrote:
> One of the problems I have thought about for a while is how to
> implement multi-dimensional array indexing efficiently. I have been
> playing with Torch recently where I noticed that Lua tables are often
> used as small sets of integer values representing tensor dimensions
> etc.
>
> I think it may be possible to have an optimized special case of small
> table as follows:
>
> If the table contains 1,2 or 3 int values, pack these into the TValue
> itself - without any heap allocation. Then it will be quite cheap to
> create these small table objects.
>
> Of course this is just an initial thought and there are undoubtedly
> implementation issues I have not foreseen.
>
> Regards
> Dibyendu

A TValue is only 4+8=12 bytes (though require 16 byte alignment).
How do you propose to fit 1,2 or 3 int values in there? You can barely
fit one 64bit integer.