Re: [boost] [endian] swap_in_place use case

Subject: Re: [boost] [endian] swap_in_place use case
From: Michael Caisse (boost_at_[hidden])
Date: 2010-06-04 14:37:54

vicente.botet wrote:
> Hi,
>
> I'm looking for a use case where the use of swap_in_place (or whatever is renamed) is not followed/preceded by a copy. 
>
>   

<snip>

> Can somene help me to identify a real use case on which the swap_in_place can be used to reveive a message, without needing to do any additional copy from the swapped buffer to native data?
>
> Thanks,
> _____________________
> Vicente Juan Botet Escribá
> http://viboes.blogspot.com/
>   

Hello Vicente -

I hope you are doing well. It was a pleasure to meet you at boostcon.

I think one problem might be the focus on "messaging" as the reason for 
endian swapping. Granted, that is a large use case and one that I 
suspect most of us use. I also do a fair amount of swapping of 
bytes/bits in signal processing work. Typically I have received some 
signal via a DMA transfer and now need to operate on it. As much as 
possible this is done in-place.

Typical operations include changing the endian to match the processor. 
For example, many PCM codecs will result in a little endian audio 
signal; however, most of my favorite processors are big endian. The swap 
will be in-place.

Another typical operation is time decimation for a Fourier transform 
which is basically bit-reversal of the indexes. This is also in-place.

Even my messaging for these small embedded processors is in-place. I 
just don't have the memory nor cycles to make copies. A message is 
formed in memory. It is "transformed" to the right endian and then the 
buffer is sent to a DMA engine.

I could provide dozens of use-cases of in-place endian transforms. Just 
start thinking little to no memory and not a lot of processor cycles and 
you can come up with a bunch.

Hope this helps a little. The endian library is of great interest to me. 
I'm reading all of the email traffic but don't have the time right yet 
to jump into the discussion.

michael

-- 
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Michael Caisse
Object Modeling Designs
www.objectmodelingdesigns.com