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Re: [Discuss-gnuradio] What value is in in[noutput_items+1]?


From: West, Nathan
Subject: Re: [Discuss-gnuradio] What value is in in[noutput_items+1]?
Date: Mon, 1 May 2017 14:48:29 -0400

That block calls set_history(2), so in[0] is actually the last sample in 'in' from the previous call to work.

On Mon, May 1, 2017 at 2:09 PM, Ghost Op <address@hidden> wrote:
I was looking back over the Quadrature Demod code and I happened to
notice something unusual.  The call to the Volk multiply conjugate
routine appears to use in[noutput_items+1] on the last calculation.

Here's the call:
volk_32fc_x2_multiply_conjugate_32fc(&tmp[0], &in[1], &in[0], noutput_items);

It obviously works correctly, and the buffer's bigger than
noutput_items so it doesn't seem to cause a memory access issue.

So my question is: when volk uses the memory at in[noutput_items+1]
what value is it using?  Is it using a zeroed byte, something from a
history buffer, or whatever happened to be there?

Would anyone have any insight?

Thanks!

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