Re: [Psyco-devel] Dynamic arrays, Pyrex and Psyco

[Tim H. <tim...@ie...>]

Armin Rigo wrote:

>Hello,
>
>On Mon, Jun 09, 2003 at 10:27:52PM +0000, sdfrost@UCSD.EDU wrote:
>  
>
>>As I imagine that lots of people would like to use Pyrex and/or Psyco to 
>>reduce the overhead of Python loops, I'm attaching a modified primes example, 
>>in which the size of the array of results is determined at runtime, and 
>>compared the performance with standard Python code and Psyco-accelererated 
>>code.
>>    
>>
>
>Note that Psyco performs better if you write the loops in a more Pythonic 
>style (which is an example of what I like to emphasis: given good tools it is 
>in the *interest* of performance to write higher-level code) :
>  
>

Oddly I don't see this speedup here: Windows XP using Psyco 1.0 on 
Python 2.2.2.  The resulting code is easier to read but roughly the same 
speed or maybe just a tad slower.    Have there been some speedups since 
1.0 was put out?

Perversely, where I do get a signifigant speed up is replacing "n % p1 
== 0" with "(n // p1) * p1 == n". This speeds things up by almost 15%. I 
know that Python needs to jump through some hoops to make modulo work 
the Python way instead of the C way, and I assume that's what's slowing 
things down.  If that really is the cause of the slowdown, would it be 
possible to recognize the "A % B == 0" case and use the raw C modulus 
there?

I was going to try the latest version from CVS and see if it was faster 
and if there were any obvious bottlenecks involving modulus, but I can't 
get it to compile here. The compiler complains about not being able to 
find iencoding.h in vcompiler.h. Any hints for where I could find myself 
an iencoding.h file for cheap?

-tim


>def primes(kmax):
>  p = []
>  n = 2
>  while len(p) < kmax:
>    for p1 in p:
>      if n % p1 == 0:
>        break
>    else:
>      p.append(n)
>    n = n + 1  
>  return p
>
>With Psyco, this only needs 80% of the time needed by your original example.  
>Surely enough Pyrex is still faster.
>
>
>A bientôt,
>
>Armin.
>
>
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>  
>