From c28495fc7dd1b010ffd171ec452b5ed2127f0008 Mon Sep 17 00:00:00 2001
From: Neil Gershenfeld <gersh@cba.mit.edu>
Date: Sun, 1 Mar 2020 19:58:19 -0500
Subject: [PATCH] wip
---
C++/threadpi.cpp | 38 ++++++++++++++++++++++++++++++++++++++
README.md | 1 +
2 files changed, 39 insertions(+)
create mode 100755 C++/threadpi.cpp
diff --git a/C++/threadpi.cpp b/C++/threadpi.cpp
new file mode 100755
index 0000000..0b6e285
--- /dev/null
+++ b/C++/threadpi.cpp
@@ -0,0 +1,38 @@
+//
+// 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;
+ }
diff --git a/README.md b/README.md
index 9539bfd..a4ce0b0 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,7 @@
|1,090|[numbapig.py](Python/numbapig.py)|Python, Numba, CUDA, 5120 cores|NVIDIA V100|March 1, 2020|
|315|[numbapip.py](Python/numbapip.py)|Python, Numba, parallel, fastmath<br>96 cores|Intel 2x Xeon Platinum 8175M|Feb 7, 2020|
|272|[threadpi.c](C/threadpi.c)|C, 96 threads<br>gcc threadpi.c -o threadpi -O3 -ffast-math -pthread|Intel 2x Xeon Platinum 8175M|Jun 3, 2019|
+|267|[threadpi.cpp](C++/threadpi.cpp)|C++, 96 threads<br>g++ threadpi.cpp -o threadpi -O3 -ffast-math -pthread|Intel 2x Xeon Platinum 8175M|Mar 1, 2020|
|211|[mpipi2.c](MPI/mpipi2.c)|C, MPI, 1 node, 96 cores<br>mpicc mpipi2.c -o mpipi2 -O3 -ffast-math|Intel 2x Xeon Platinum 8175M|Oct 24, 2019|
|180|[mpipi2.py](Python/mpipi2.py)|Python, Numba, MPI<br>mpirun -np 96 python mpipi2.py|Intel 2x Xeon Platinum 8175M|Feb 6, 2020|
|173|[mppi.c](OpenMP/mppi.c)|C, OpenMP, 96 threads<br>gcc mppi.c -o mppi -O3 -ffast-math -fopenmp|Intel 2x Xeon Platinum 8175M|Jul 1, 2019|
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