[Numpy-discussion] Deprecating PyDataMem_RENEW ?

[David Cournapeau]

Hi,

    While working again on the fftpack module, to clean things up and 
speed some backends (in particular fftw3, which is really sub-optimal 
right now), I remembered how much unaligned data pointer in numpy arrays 
hurt performances. So I would like to relaunch the discussion on aligned 
allocators and default alignement for numpy arrays :

http://www.mail-archive.com/numpy-discussion@scipy.org/msg04005.html

Basically, what I have in mind is, in a first step (for numpy 1.2):
    - define functions to allocate on a given alignement
    - make PyMemData_NEW 16 byte aligned by default (to be compatible 
with SSE and co).

The problem was, and still is, realloc. It is not possible to implement 
realloc with malloc/free (in a portable way), and as such, it is not 
possible to have an aligned realloc.

In numpy, we can always replace realloc by malloc/free, because we know 
the size of the old block: would deprecating PyMemData_RENEW and 
replacing them by PyMemeData_NEW/PyMemData_FREE be possible, such as to 
make all numpy arrays follow a default alignement ? There are only a few 
of them in numpy (6 of them), 0 in scipy, and I guess extensions never 
really used them ?

cheers,

David