Add stable sort demo.

demo_stable_sort.cpp

@@ -0,0 +1,73 @@
+// compile with:
+//    debug: cl /EHsc /W4 /WX /std:c++latest /Festable_sort_debug /MDd /Zi .\demo_stable_sort.cpp
+//  release: cl /EHsc /W4 /WX /std:c++latest /Festable_sort_release /MD /Zi /O2 .\demo_stable_sort.cpp
+#include <stddef.h>
+#include <stdio.h>
+#include <algorithm>
+#include <chrono>
+#include <execution>
+#include <ratio>
+#include <random>
+#include <charconv>
+#include <vector>
+
+using namespace std; // sorry Titus
+using namespace std::chrono;
+using namespace std::execution;
+
+const int iterationCount = 10;
+
+template<class ExPo>
+steady_clock::duration run_stable_sort(vector<double>& doubles, ExPo&& ex,
+	const char * const tag) {
+	steady_clock::duration totalTime{};
+	for (int i = 0; i < iterationCount; ++i)
+	{
+		const auto startTime = steady_clock::now();
+		stable_sort(forward<ExPo>(ex), doubles.begin(), doubles.end());
+		const auto endTime = steady_clock::now();
+		totalTime += endTime - startTime;
+		printf("%s: Min: %g Max: %g Time: %gms\n", tag, doubles.front(), doubles.back(),
+			duration_cast<duration<double, milli>>(endTime - startTime).count());
+	}
+
+	return totalTime;
+}
+
+void print_diff(const char * const name,
+	const steady_clock::duration baselineTime,
+	const steady_clock::duration compareTime) {
+	const char * direction;
+	double times;
+	if (baselineTime < compareTime) {
+		times = static_cast<double>(compareTime.count()) / baselineTime.count();
+		direction = "slower";
+	}
+	else {
+		times = static_cast<double>(baselineTime.count()) / compareTime.count();
+		direction = "faster";
+	}
+
+	printf("%s was %g times %s\n", name, times, direction);
+}
+
+int main(int argc, char **argv) {
+	if (argc != 2) { printf("Usage: %s number\n", argv[0]); return 1; }
+	size_t testSize;
+	auto[ptr, ec] = from_chars(argv[1], argv[1] + strlen(argv[1]), testSize);
+	if (ec != errc{}) { printf("Bad %s parse as integer.\n", argv[1]); return 2; }
+
+	// generate some doubles:
+	printf("Testing with %zu doubles (%gmb)...\n", testSize,
+		static_cast<double>(testSize) * sizeof(double) / (1024*1024));
+	vector<double> doubles;
+	doubles.reserve(testSize);
+	minstd_rand lce(1729);
+	for (size_t idx = 0; idx < testSize; ++idx) {
+		doubles.push_back(lce());
+	}
+	// time how long it takes to stable_sort them:
+	const auto serialTime = run_stable_sort(doubles, seq, "Serial");
+	const auto parallelTime = run_stable_sort(doubles, par, "Parallel");
+	print_diff("Parallel", serialTime, parallelTime);
+}