Terrible FPU performance

Tue Apr 26 09:40:36 EDT 2011

Hi,
I have terrible performance for multiplication when one number gets very
close to zero. I'm using cython by writing the following code:
 cdef int i
 cdef double x = 1.0
 for 0 <= i < 10000000:
 x *= 0.8
 #x += 0.01
 print x
This code runs much much slower (20+ times slower) with the line x += 0.01
uncommented. I looked at the deassembled code and it looks correct.
 Moreover, it's just a few lines and by writing a C code (without python on
top), I get the same code, but it's much faster. I've also tried using sse,
but I get exactly the same behavior. The best candidate that I see so far
is that Python sets up the FPU in a different state than C.
Any advice on how to solve this performance problem?
thanks!
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