[Numpy-discussion] Re: Bytes Object and Metadata

Francesc Altet faltet at carabos.com
Tue Mar 29 05:24:24 CST 2005


A Dilluns 28 Març 2005 23:54, Perry Greenfield va escriure:
> Numarray, when it uses the buffer object, always gets a fresh pointer
> for the buffer object for every data access. But Scott is right that
> that pointer is good so long as there isn't a chance for something else
> to change it. In practice, I don't think that ever happens with the
> buffers that numarray happens to use, but it's still a flaw of the
> current buffer object that there is no way to ensure it won't change.

However, having to update the pointer for the buffer object for every
data access does impact performance quite a lot.

This issue has been brought up to this list some months ago (see [1]).
I, as for one, have renounced to call NA_updateDataPtr() during table
reads in PyTables and this speeded up the reading process by 70%,
which is not a joke. And this speed-up could be theoretically achieved
in every piece of code that reads like:

for i range(n):
    a = numarrayobject[i]
    
that is, whenever a single element in array is accessed.

If the bytes object suggested by Scott makes the call to
NA_updateDataPtr() unnecessary then this is an added advantage of
bytes over buffer.

[1] http://sourceforge.net/mailarchive/message.php?msg_id=8848962

Cheers,

-- 
>qo<   Francesc Altet     http://www.carabos.com/
V  V   Cárabos Coop. V.   Enjoy Data
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