[PD] how to iterate over left and right channel separately in one Pd class?

[Hans-Christoph Steiner]

I recently learned that libc's memcpy actually uses things like SSE2 or SSSE2
so it can be quite fast on CPUs from the past 10 years, especially of the last
5 years.

It would be worth profiling to see if that's noticeable.

.hc

On 01/11/2013 05:12 PM, katja wrote:
> Ok so I did the ugly thing with the right channel input and output pointers:
> 
> memcpy(outR, inR, vectorsize * sizeof(t_float));
> inR = outR;
> 
> Works like a charm, thanks again.
> 
> Katja
> 
> 
> 
> On Fri, Jan 11, 2013 at 10:05 PM, Miller Puckette <msp at ucsd.edu> wrote:
>> copy_perform assumes the data is 4-byte aligned so might save a test
>> or two compared to memcopy() - but I really don't know.  I never
>> benchmarked the two against each other :)
>>
>> M
>>
>> On Fri, Jan 11, 2013 at 09:36:41PM +0100, katja wrote:
>>> Hi Miller,
>>>
>>> Thanks for the solution. The routines are in place so copying the
>>> right channel input to output should do it. Is there any reason to
>>> prefer copy_perform() over memcpy()? I'm trying to make the most
>>> efficient reverb for RPi & Co.
>>>
>>> Katja
>>>
>>>
>>>
>>> On Fri, Jan 11, 2013 at 7:57 PM, Miller Puckette <msp at ucsd.edu> wrote:
>>>> Hi Katja -
>>>>
>>>> There's one example of this in sigfft_dspx() - a complex FFT that 'natively'
>>>> works on 2 signals in-place but has to deal with various cases in which
>>>> buffers get re-used.  It's ugly but the basic idea is first to get the
>>>> inputs copied to the outputs (unless they're already there in the correct
>>>> order in which case nothing needs to be done) and then run the in-place
>>>> algorithm.
>>>>
>>>> If the algo only works out-of-place (i.e. you need 4 distinct buffers, 2
>>>> in and 2 out) the only way out is (at least conditionally) allocate temporary
>>>> copies of the inputs before writing to any outputs.
>>>>
>>>> I may be able to add an optional way tilde objects can request that output
>>>> buffers be distinct from input ones sometime in the future - but this is a
>>>> couple of steps away for me right now :)
>>>>
>>>> M
>>>>
>>>> On Fri, Jan 11, 2013 at 03:32:09PM +0100, katja wrote:
>>>>> Hello,
>>>>>
>>>>> I'm working on a Pd class with stereo channels (reverb), and the
>>>>> routine happens to be most efficient when iterating over the samples
>>>>> per channel, instead of left and right together in the perform loop.
>>>>> However, when doing two while loops in one object, one for left and
>>>>> one for right, the right channel samples get overwritten because of
>>>>> sample-wise in-place computation. Is this an inescapable truth? I
>>>>> mean, I could write a left channel class and a right channel class
>>>>> (actually did that to verify that it works), but it's inconvenient to
>>>>> use. What could be an efficient way to get them in one object?
>>>>>
>>>>> Thanks,
>>>>> Katja
>>>>>
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