Re: [ctypes-users] copying/slicing ctypes arrays, (c_ulong *n)()

[Thomas H. <th...@py...>]

RayS <ra...@bl...> writes:

> Thanks Florian,
>
> My preliminary assessment from trials yesterday (based only on a rough
> benchmark of idle time) is that
>         for i in range(2000): numArray[pntr+i] = buf[i]
> is >10x slower than
>         numArray[pntr:pntr+2000] = map(None, buf)
> which is 25% slower than using array.array() & memmove
>         memmove(array.buffer_info()[0]+pntr, buf)
>

Do I understand it correctly that memmove is only slightly faster than
the 'numArray[..] = map(None, buf)' call?  If so, interesting.

> I'll test the direct assignment today, as below, as subsequent
> operations on numarray should be faster than array. I don't recall why
> I didn't.
>
> The numarray buffer interface is interesting, but I mainly need to do
> a (deep) copy out of the ctypes memory.  Since the main issue is that
> src (the ctypes obj) is being updated with 2KB A/D data @125x per
> second (250K samp./s), I need to get it out of the cytpes obj into
> storage as efficiently as possible. That storage must then work with
> slicing and FFT.
>
> If the ctypes construct buf = (c_ulong * 2000)() supported slicing, I
> would just leave it there...

But it *should* support slicing.  Can't you write this instead of the map() call?

    numArray[pntr:pntr+2000] = buf[0:2000]

Another possibility would be to let the ADC write the data directly into
the numArray, once you know it's address (and assuming it doesn't
change).

Thomas