[mailto:haskell-cafe-bounces@haskell.org] 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: http://www.haskell.org/haskellwiki/Performance/GHC#Crank_up_the_gcc_flag s http://www.haskell.org/haskellwiki/Performance/Floating_Point Alistair ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

* Andrew Coppin [070608 02:45]:

Bayley, Alistair wrote:

[[1]mailto:haskell-cafe-bounces@haskell.org] 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 Results with -fexcess-precision are very insignificantly different (1.0 e-7).

dons:

sic:

...

* Andrew Coppin [070608 02:45]:

...

Bayley, Alistair wrote:

[[1]mailto:haskell-cafe-bounces@haskell.org] 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

My apologies. Misread that last line. /me drinks more tea. -- Don

[mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Donald Bruce Stewart

3) -fbang-patterns

Better than `seq`

Better in the "more convenient to write" sense, right? AFAIUI, seq and bang patterns should be equivalent. Alistair ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

3) -fbang-patterns Better than `seq` Do you mean "more convenient than" or "generates better code than". I don't think the latter should be true; send a counterexample if you find one! Simon