[Cython] ctypes Vs Cython

[Sebastien Binet]

hi,

On Wednesday 13 May 2009 08:35:27 Robert Bradshaw wrote:
> On May 12, 2009, at 9:47 PM, Mohamed Lrhazi wrote:
> > On Wed, May 13, 2009 at 12:31 AM, Chris Colbert
> >
> > <sccolbert at gmail.com> wrote:
> >> If your making lots of rapid calls to short running functions in the
> >> C-library, then you may start to feel the ctypes overhead.
> >
> > That's what I was afraid to hear..
>
> Hopefully after using Cython a bit, you're fears will quickly go
> away :).
>
> > What I was hoping to hear is "Oh
> > no, ctypes is all C anyways, and will perform just the same as Cython"
>
> A simple benchmark:
>
> import ctypes
> libm = ctypes.cdll.LoadLibrary("libm.dylib") # platform dependent...
> def ctypes_sum(N):
>      lib_sqrt = libm.sqrt
>      lib_sqrt.argtypes = (ctypes.c_double,)
>      lib_sqrt.restype = ctypes.c_double
>      s = 0
>      for i in range(N):
>          s += lib_sqrt(i)
>      return s
>
> %cython
> cdef extern from "math.h":
>      double sqrt(double)
>
> def cython_sum(long N):
>      cdef int i
>      cdef double s=0
>      for i in range(N):
>          s += sqrt(i)
>      return s
>
>  >>> time ctypes_sum(10**6)
>
> 666666166.4588418
> Time: CPU 1.13 s, Wall: 1.14 s
>
> time cython_sum(10**6)
> 666666166.4588418
> Time: CPU 0.03 s, Wall: 0.03 s

interesting simple minded benchmark :)

how would this translate into the pure-python mode ? (I couldn't seem to be 
able to declare the C-sqrt function using the pure-python mode of cython:
http://wiki.cython.org/pure wasn't helpful)

cheers,
sebastien.
-- 
#########################################
# Dr. Sebastien Binet
# Laboratoire de l'Accelerateur Lineaire
# Universite Paris-Sud XI
# Batiment 200
# 91898 Orsay
#########################################