[Discuss-gnuradio] How history() works in GR

Hello

I am trying to define a customised block and I would like to understand better how the history works.

I have opened the source of gr_moving_average_XX and I saw the following statement in the constructor:

@NAME@::@NAME@ (int length, @O_TYPE@ scale, int max_iter)
: gr_sync_block ("@BASE_NAME@",
gr_make_io_signature (1, 1, sizeof (@I_TYPE@)),
gr_make_io_signature (1, 1, sizeof (@O_TYPE@))),
d_length(length),
d_scale(scale),
d_max_iter(max_iter),
d_new_length(length),
d_new_scale(scale),
d_updated(false)
{
set_history(length);
}

So it seems to me that GR allocates a history buffer with "length" size.
But, later in the gr_moving_average_XX code I see the following cycle:

for (int i = 0; i < num_iter; i++) {
sum += in[i+d_length-1];
out[i] = sum * d_scale;
sum -= in[i];
}

...which seems to show that there is at least a buffering of "length + num_iter" input items somewhere, and num_iter
is >0 for sure.
This has confused me a bit on how history is implemented.

Thanks for any explanation.

Alberto

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