On 01.12.2013 22:59, Dan Goodman wrote:
> Julian Taylor <jtaylor.debian <at> googlemail.com> writes:
>> your sin and exp calls are loop invariants, they do not depend on the
>> loop iterable.
>> This allows to move the expensive functions out of the loop and only
>> leave some simple arithmetic in the body.
>
> Ahhhh! I feel extremely stupid for not realising this! Thanks Julian.
>
> Any thoughts on why using -ffast-math it actually goes slower for just doing
> sin(x)?
>
no on my linux machine ffast-math is a little faster:
numpy: 311 ms
weave_slow: 291 ms
weave_fast: 262 ms
here is a pure numpy version of your calculation which only performs 3
times worse than weave:
def timefunc_numpy2(a, v):
ext = exp(-dt/tau)
sit = sin(2.0*freq*pi*t)
bs = 20000
for i in range(0, N, bs):
ab = a[i:i+bs]
vb = v[i:i+bs]
absit = ab*sit + b
vb *= ext
vb += absit
vb -= absit*ext
it works by replacing temporaries with inplace operations and blocks the
operations to be more memory cache friendlier.
using numexpr should give you similar results.
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