sic:
> * Andrew Coppin <[EMAIL PROTECTED]> [070608 02:45]:
> > Bayley, Alistair wrote:
> >
> > [[1]mailto:[EMAIL PROTECTED] On Behalf Of Andrew Coppin
> >
> > Donald Bruce Stewart wrote:
> >
> > Some things to remember using Doubles:
> >
> > * {-# OPTIONS -fexcess-precision #-}
> > * -fvia-C
> > * -fbang-patterns
> > * -optc-O2 -optc-mfpmath=sse -optc-msse2
> > * -optc-march=pentium4
> >
> > 1. What do all those things do?
> > 2. Is the effect actually that large?
> >
> > Large? Depends what you mean by large, but adding a few flags to get
> > just a 10-20% speedup isn't to be ignored:
> >
> > Sure - if it really is 10-20%. (And not, say, 0.001 - 0.002%.)
>
> A single data point for all of this, I have a program that calculates:
>
> P^1_i = S_i/sum_k S_k
> P^m_i = sum_{k!=i} P^1_k*P^m-1_i(S_~k)
>
> Here's timings for the different options:
>
> options run time compile time
> none 46.401 3.136
> -O 5.033 4.906
> -O2 4.967 6.755
> -O2 -fexcess-precision 3.710 6.396
> all listed options 3.602 6.344
>
Due to a (now fixed in 6.6.1 I think) bug in GHC 6.6, -fexcess-precision
*must* be inserted in a pragma. Did you do that?
{-# OPTIONS -fexcess-precision #-}
See the bug report here,
http://hackage.haskell.org/trac/ghc/ticket/1138
-- Don
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