Re: [Caml-list] Conditionally boxed 32 bit integers?

[Gerd Stolpmann <info@gerd-stolpmann.de>]

Am Sonntag, den 04.09.2011, 11:22 -0400 schrieb John Carr:
> I am working with a file format the contains 32 bit integers.
> I need to use int32 on 32 bit systems.  I would like to use plain
> integers, unboxed and with native machine operations, on 64 bit
> systems.
> 
> Is there any way to convince ocamlopt to choose between int and
> int32 representations _at compile time_?

The Netnumber module of Ocamlnet actually does this:

https://godirepo.camlcity.org/svn/lib-ocamlnet2/trunk/code/src/netstring/netnumber.mli
https://godirepo.camlcity.org/svn/lib-ocamlnet2/trunk/code/src/netstring/netnumber.mlp

Netnumber is fairly standalone, so you could just copy it to your
project if you don't want all of Ocamlnet.

Gerd


> 
> I could use first class modules to select implementations at
> runtime, which is not worth the code complexity and still
> requires an indirect function call to add numbers.  I could
> conditionally compile different files depending on word size,
> which strikes me as an ugly and fragile solution.
> 
> I want to be able to write "int32" and have that be compiled
> like an ordinary integer type if 32 bits and tag fit into a
> word, and as a boxed type otherwise.  (The compiler could
> mask off excess precision if desired.)  Is there a reason ocaml
> can't provide this?
> 
> Another implementation would have each instance of an int32 or
> int64 be boxed or not depending on whether the value fits into
> a word.  I don't know whether this would be faster or slower in
> practice.  There is a tradeoff between allocations and
> conditional branches.
> 
>     --John Carr (jfc@mit.edu)
> 

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