[Haskell-cafe] Re: Why 'round' does not just round numbers ?
s.clover at gmail.com
Fri Oct 31 20:41:50 EDT 2008
On Oct 30, 2008, at 5:21 PM, Bertram Felgenhauer wrote:
> George Pollard wrote:
>> There's also the ieee-utils package, which provides an IEEE monad
> When run with +RTS -N2 -RTS, the output randomly alternates
> between Downward and ToNearest - for me at least.
> The problem is that the setRound call will only affect one worker
> thread, while the RTS will sometimes migrate RTS threads from one
> worker to another.
> runIEEE really has to be executed in a bound thread (see forkOS
> documentation). Using `par` will also cause trouble - in fact even
That's a really nice catch!
Dons has pointed out to me both the very handy forkOnIO which ensures
the forked thread remains bound to a single CPU, and also the -qm
flag to the RTS, which prevents thread migration between
capabilities. Running the example program with +RTS -N2 -qm restores
the behavior to what's intended. I'll try to get around to changing
the documentation to reflect this. Also, it's worth noting that the
IEEE round mode has no effect on rounding done with the `round`
function, as that's explicitly coded to provide the behavior seen in
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