More primops for integer arithmetic with overflow reporting

[Ian Lynagh]

Hi hvr,

On Tue, Jan 10, 2012 at 12:05:51PM +0100, Herbert Valerio Riedel wrote:
> 
> As the {Int,Word}{,8,16,32,64} types in Haskell are usually regarded to
> follow modulo arithmetic (w.r.t. to the Num-class ops), I was trying to
> implement efficient non-modulo Safe{Int,Word}{,8,16,32,64} types which
> would throw exceptions when the result falls outside the value domain
> representable.

Are you aware of http://hackage.haskell.org/package/safeint ?

> As ISAs often have hardware support to detect such overflows (e.g. on
> x86-64 via the OF/CF flags), I guess that by exploiting hardware
> support, this might allow for a reasonably efficient implementation of
> non-modulo integer arithmetic.

safeint doesn't do this yet, but it's part of the plan.

> So far I've only found 'addIntC#' and 'subIntC#' which perform the kind
> of operation I'm looking for. But this is only for signed integers, and
> as far as multiplication is concerned, there's a 'mulIntMayOflo#' but
> that may provide false negatives according to the documentation.
> 
> Therefore, I was wondering whether it'd make sense for GHC to provide
> more primops for the {Int,Word}{,8,16,32,64} types which return the
> result value together with an overflow-flag.

This is also relevant:
    http://hackage.haskell.org/trac/ghc/ticket/5598


Thanks
Ian