Optimize circular buffer shift in the C++ implementation

[jurihock]

As mentioned in my comment, the std::rotate is most likely a major performance issue.

Actually there is no measurable difference between the following variations:

• std::rotate(inputs.begin(), inputs.begin() + 1, inputs.end());
• std::copy(inputs.begin() + 1, inputs.end(), inputs.begin());
• std::shift_left(inputs.begin(), inputs.end(), 1);

But instead of std::vector use std::deque to shift the buffered values like so:

• inputs.pop_front();
• inputs.push_back(sample);

The complexity of the linear/random element access as well as insertion or removal of elements at both ends of the std::deque should be still O(1).

[jurihock]

Benchmark

Test case:

• analysis.cpp
• no data plot
• linear chirp
• signal duration 10s

Results:

• cmake -DCMAKE_BUILD_TYPE=Release .. && cmake --build . && time ./qdft-example-analysis
• std::vector ➡ 2.57s user 0.13s system 99% cpu 2.698 total
• std::deque ➡ 0.37s user 0.11s system 99% cpu 0.486 total

std::deque is clearly the winner!