Comments on: Reliability with Erlang http://steve.vinoski.net/blog/2007/10/31/reliability-with-erlang/ Ask forgiveness, not permission. Sun, 07 Sep 2008 17:31:32 +0000 http://wordpress.org/?v=2.6.1 By: Mike Giroux http://steve.vinoski.net/blog/2007/10/31/reliability-with-erlang/#comment-257 Mike Giroux Wed, 07 Nov 2007 18:29:38 +0000 http://steve.vinoski.net/blog/2007/10/31/reliability-with-erlang/#comment-257 PS: Yes, I realize that without the unrolling, Square*Square will be computed once too often by the "generic" geometric_pow/3. But the slowness happened even with versions of geometric_pow/3 that didn't have that problem. Very strange... PS: Yes, I realize that without the unrolling, Square*Square will be computed once too often by the “generic” geometric_pow/3. But the slowness happened even with versions of geometric_pow/3 that didn’t have that problem. Very strange…

]]> By: Mike Giroux http://steve.vinoski.net/blog/2007/10/31/reliability-with-erlang/#comment-254 Mike Giroux Tue, 06 Nov 2007 12:42:03 +0000 http://steve.vinoski.net/blog/2007/10/31/reliability-with-erlang/#comment-254 Steve, Nice articles, thanks. I'm trying to learn Erlang, and having fun. One entertaining exercise was trying to speed up pow. Obviously, doing pow linearly shouldn't be faster than doing a "binary exponentiation" pow computation. http://en.wikipedia.org/wiki/Exponentiation_by_squaring What was driving me crazy is that although this algorithm is O(lg n) and the other pow is O(n), I had a heck of a time getting a powers of 2 implementation that beat the linear one in erlang. I had to "unroll" the last few levels of my function to explicitly match exponents 1, 2, and 3 before this approach started to win. This final implementation wins big, though, and also has a big advantage in terms of the largest power that can be computed. Trying to compute pow(5000,50000) on my mac runs out of memory, but geometric_pow(5000,50000) computes it in 2.7 seconds. Here's the implementation: % Licensed under Artistic License, see % http://www.perl.com/pub/a/language/misc/Artistic.html % Mike Giroux, rmgiroux@gmail.com -module(geometric_pow). -export([geometric_pow/2]). geometric_pow(_, 0, Acc) -> Acc; % It's interesting that if 1 and 2 aren't "unrolled", % the linear implementation beats geometric_pow. geometric_pow(Square, 1, Acc) -> Square*Acc; geometric_pow(Square, 2, Acc) -> Square*Square*Acc; geometric_pow(Square, 3, Acc) -> Square*Square*Square*Acc; geometric_pow(Square, 4, Acc) -> Square*Square*Square*Square*Acc; geometric_pow(Square, Exp, Acc) -> geometric_pow(Square*Square, Exp div 2, ((Exp rem 2)*(Square-1)*Acc + Acc)). geometric_pow(Base, Exponent) -> geometric_pow(Base,Exponent,1). Steve,

Nice articles, thanks. I’m trying to learn Erlang, and having fun.

One entertaining exercise was trying to speed up pow.

Obviously, doing pow linearly shouldn’t be faster than doing a “binary exponentiation” pow computation.

http://en.wikipedia.org/wiki/Exponentiation_by_squaring

What was driving me crazy is that although this algorithm is O(lg n) and the other pow is O(n), I had a heck of a time getting a powers of 2 implementation that beat the linear one in erlang.

I had to “unroll” the last few levels of my function to explicitly match exponents 1, 2, and 3 before this approach started to win.

This final implementation wins big, though, and also has a big advantage in terms of the largest power that can be computed. Trying to compute pow(5000,50000) on my mac runs out of memory, but geometric_pow(5000,50000) computes it in
2.7 seconds.

Here’s the implementation:

% Licensed under Artistic License, see
% http://www.perl.com/pub/a/language/misc/Artistic.html
% Mike Giroux, rmgiroux@gmail.com

-module(geometric_pow).
-export([geometric_pow/2]).

geometric_pow(_, 0, Acc) -> Acc;
% It’s interesting that if 1 and 2 aren’t “unrolled”,
% the linear implementation beats geometric_pow.
geometric_pow(Square, 1, Acc) -> Square*Acc;
geometric_pow(Square, 2, Acc) -> Square*Square*Acc;
geometric_pow(Square, 3, Acc) -> Square*Square*Square*Acc;
geometric_pow(Square, 4, Acc) -> Square*Square*Square*Square*Acc;
geometric_pow(Square, Exp, Acc) ->
geometric_pow(Square*Square, Exp div 2, ((Exp rem 2)*(Square-1)*Acc + Acc)).

geometric_pow(Base, Exponent) ->
geometric_pow(Base,Exponent,1).

]]> By: Darach http://steve.vinoski.net/blog/2007/10/31/reliability-with-erlang/#comment-234 Darach Fri, 02 Nov 2007 23:12:25 +0000 http://steve.vinoski.net/blog/2007/10/31/reliability-with-erlang/#comment-234 I've built strategized fast-fail into asynchronous FSMs in trading platforms as a default transition. When you have 40+ states and 100s of state-changing transitions in a state machine it gets hard to test every single possible race condition due to the size of the state space involved. Either way Steve/Lauri you've both convinced me to pick up the book! Also, it seems FSM's are very well supported in erlang: http://portal.acm.org/ft_gateway.cfm?id=1292529&type=pdf&coll=GUIDE&dl=&CFID=15151515&CFTOKEN=6184618 I’ve built strategized fast-fail into asynchronous FSMs in trading platforms as a default transition. When you have 40+ states and 100s of state-changing transitions in a state machine it gets hard to test every single possible race condition due to the size of the state space involved.

Either way Steve/Lauri you’ve both convinced me to pick up the book! Also, it seems FSM’s are very well supported in erlang:

http://portal.acm.org/ft_gateway.cfm?id=1292529&type=pdf&coll=GUIDE&dl=&CFID=15151515&CFTOKEN=6184618

]]> By: Patrick Logan http://steve.vinoski.net/blog/2007/10/31/reliability-with-erlang/#comment-230 Patrick Logan Fri, 02 Nov 2007 00:11:58 +0000 http://steve.vinoski.net/blog/2007/10/31/reliability-with-erlang/#comment-230 I prefer ErUnit over EUnit. It was simply easier for me to start using. http://bestfriendchris.com/blog/2007/04/23/erunit-unit-testing-for-erlang/ Not sure about feature comparison. I don't demand much of a unit test framework. I prefer ErUnit over EUnit. It was simply easier for me to start using.

http://bestfriendchris.com/blog/2007/04/23/erunit-unit-testing-for-erlang/

Not sure about feature comparison. I don’t demand much of a unit test framework.

]]> By: James Abley http://steve.vinoski.net/blog/2007/10/31/reliability-with-erlang/#comment-228 James Abley Thu, 01 Nov 2007 21:29:53 +0000 http://steve.vinoski.net/blog/2007/10/31/reliability-with-erlang/#comment-228 Do you have any thoughts on Erlang's test frameworks? Something that put me off learning Lisp for a very long time was the lack of LispUnit, but I eventually persevered with Peter Seibel's <a href="http://www.gigamonkeys.com/book/" rel="nofollow">excellent book</a>. I'm going through Joe's book now, and all I've found thus far is "write a makefile that exercises the code with test code". It feels a bit far off JUnit, ANT and Ivy, and that worries me. Should it? Do you have any thoughts on Erlang’s test frameworks? Something that put me off learning Lisp for a very long time was the lack of LispUnit, but I eventually persevered with Peter Seibel’s excellent book. I’m going through Joe’s book now, and all I’ve found thus far is “write a makefile that exercises the code with test code”. It feels a bit far off JUnit, ANT and Ivy, and that worries me. Should it?

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