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Seed the PRNG: --seed N, default random, printed for reproducibility #7

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Seed the PRNG: --seed N, default random, printed for reproducibility #7

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19 changes: 19 additions & 0 deletions main.cpp
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Original file line number Diff line number Diff line change
@@ -1,7 +1,9 @@
#include "PathSimProcessor.h"
#include "PathSimParams.h"

#include <cstdlib>
#include <iostream>
#include <random>
#include "cxxopts.h"
#include "AudioFile.h"

Expand Down Expand Up @@ -37,6 +39,9 @@ from a Windows GUI application by Moe Wheatley, AE4JY, 2000\n\
}

options.add_options("Propagation")
("seed", "PRNG seed for the fading/noise processes (default: random; "
"the seed used is printed so any run can be reproduced exactly)",
cxxopts::value<unsigned int>())
("snr", "Signal to Noise Ratio (SNR)", cxxopts::value<double>())
("spread", "Frequency spread of the 1st path [Hz]", cxxopts::value<double>())
("offset", "Frequency offset of the 1st path [Hz]", cxxopts::value<double>())
Expand All @@ -56,6 +61,20 @@ from a Windows GUI application by Moe Wheatley, AE4JY, 2000\n\
exit(0);
}

// Seed the PRNG behind the Rayleigh fading and AWGN stages. Without
// this, rand() runs from its default seed and EVERY invocation
// produces bit-identical "random" fading and noise — N runs give one
// realization N times, silently defeating ensemble statistics.
// Default is a fresh random seed; it is printed (stderr, so pipes
// stay clean) so any run can be reproduced with --seed.
{
unsigned int seed = result.count("seed")
? result["seed"].as<unsigned int>()
: std::random_device{}();
std::srand(seed);
std::cerr << "pathsim: seed " << seed << std::endl;
}

if (argc > 1 ||
((result.count("input_file") != 1 || result.count("output_file") != 1) &&
result.arguments().size() != 2)) {
Expand Down