wip

C++/threadpi.cpp

+//
+// threadpi.cpp
+// Neil Gershenfeld 3/1/20
+// calculation of pi by a C++ thread sum
+// pi = 3.14159265358979323846 
+//
+#include <iostream>
+#include <chrono>
+#include <thread>
+#include <vector>
+unsigned int npts = 2e7;
+unsigned int nthreads = std::thread::hardware_concurrency();
+std::vector<double> results(nthreads);
+void sum(int index) {
+   unsigned int start = npts*index+1;
+   unsigned int end = npts*(index+1)+1;
+   double result = 0;
+   for (unsigned int i = start; i < end; ++i)
+      result += 0.5/((i-0.75)*(i-0.25));
+   results[index] = result;
+   }
+int main(void) {
+   double pi = 0;
+   std::thread threads[nthreads];
+   auto tstart = std::chrono::high_resolution_clock::now();        
+   for (int i = 0; i < nthreads; ++i)
+      threads[i] = std::thread(sum,i);
+   for (int i = 0; i < nthreads; ++i) {
+      threads[i].join();
+      pi += results[i];
+      }
+   auto tend = std::chrono::high_resolution_clock::now();        
+	auto dt = std::chrono::duration_cast<std::chrono::microseconds>(tend-tstart).count();
+   auto mflops = npts*nthreads*5.0/dt;
+   std::cout << "npts: " << npts << " nthreads: " << nthreads << " pi: " << pi << '\n';
+   std::cout << "time: " << 1e-6*dt << " estimated MFlops: " << mflops << '\n';
+   return 0;
+   }

README.md

@@ -10,6 +10,7 @@
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