Hi,
I have the following function:
float blk::func(uint16_t *argmax, gr_complex *vector, uint32_t vlen) {
cout << "0: " << vector[0] << " (" << abs(vector[0])<< ")"
<< " 996: " << vector[996] << " (" << abs(vector[996]) << ") "
<< " 999: " << vector[999] << " (" << abs(vector[999]) << ")" <<
endl;
volk_32fc_index_max_16u(argmax, vector, vlen);
const gr_complex max_mag_sample = vector[*argmax];
const float max_abs = abs(max_mag_sample);
return max_abs;
}
It works most of the time. But seldom, I have some input that causes it to
return argmax which isn't the index of the sample with the biggest
magnitude (this is reproduced between different executions - for the same
input vector, given the same conditions, the wrong argmax is returned). Any
idea what can cause it, or how to debug it?
Some info:
1. GNU Radio 3.7.11.1.
2. When I compile with -DCMAKE_BUILD_TYPE=RelWithDbgInfo (or Debug), the
issue doesn't happen.
3. When I add specific debug prints, the issue doesn't happen, but with
some debug prints I'm able to reproduce the problem. See below.
4. I have several ways to "solve" ("hide" will be a better word) the
issue, for example, moving the buffer allocation of vector to the loop body
(a loop calls the above function each iteration) seems to "solve" the
issue, but I'm concerned that it only hides a bug that will surface again
(and this is a hard bug to catch, because it doesn't crash, just returns
wrong results).
5. None of the variables I created (buffer, argmax, vlen) are
volk-aligned (weren't created using volk_malloc()).
6. volk_32fc_index_max_16u() writes 996 to argmax, while 999 is the
biggest sample (the debug print below at the least proves that the last
sample is bigger than vector[argmax]). If I try passing "vlen - 1"
(remove the last, biggest sample), I get argmax 880, which seems like
the actual 2nd biggest.
7. I'm certain about the issue because I'm able to print the values of
the samples. My vector is 1000-sample long (vlen == 1000).
8. Most inputs work as expected.
9. Oddly enough, even adding "vector[996] = 0" as the first line in the
function doesn't help: the function still chooses 996 as argmax (and I
verified that the sample is really 0)!
1. When setting the last sample to 0 (instead of #996), argmax is
chosen to be 880, so it basically seems like "if the last (#999)
sample is
the biggest, choose 996".
10. If I pass vector+1 (start at the 2nd sample) and vlen-1 (until the
end), I get the last sample (so correct results because it's the biggest).
cout << "0: " << vector[0] << " (" << abs(vector[0])<< ")"
<< " 996: " << vector[996] << " (" << abs(vector[996]) << ") "
<< " 999: " << vector[999] << " (" << abs(vector[999]) << ")" <<
endl;
->
0: (-0.00345266,-0.00122826) (0.00366463) 996: (0.000987553,0.00248463)
(0.0026737) 999: (0.0273567,0.00109235) (0.0273785)
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