Subject: Re: [boost] [endian] swap_in_place use case
From: Michael Caisse (boost_at_[hidden])
Date: 2010-06-04 14:37:54
> 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.
> 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?
> Vicente Juan Botet Escribá
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 Caisse Object Modeling Designs www.objectmodelingdesigns.com
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