wip

C/threadpi.c

+/*
+* threadpi.c
+* Neil Gershenfeld 12/17/18
+* pi calculation benchmark
+* pi = 3.14159265358979323846
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+#include <pthread.h>
+
+unsigned int npts = 1e9;
+double pi = 0;
+pthread_mutex_t mutex;
+
+struct data {
+   unsigned int index;
+   unsigned int points;
+   };
+
+void *fn(void *arg) {
+   struct data *vars;
+   unsigned int i,start,end;
+   double sum = 0;
+   double a = 0.5;
+   double b = 0.75;
+   double c = 0.25;
+   vars = (struct data *) arg;
+   start = 1+(vars->points)*(vars->index);
+   end = (vars->points)*(vars->index+1);
+   for (i = start; i <= end; ++i)
+      sum += a/((i-b)*(i-c));
+   pthread_mutex_lock(&mutex);
+   pi += sum;
+   pthread_mutex_unlock(&mutex);
+   pthread_exit(0);
+   }
+
+void main(int argc, char *argv[]) {
+   int i,nthreads;
+   nthreads = atoi(argv[1]);
+   pthread_t threads[nthreads];
+   struct data var[nthreads];
+   double dt,mflops;
+   void *status;
+   struct timespec tstart,tend;
+   clock_gettime(CLOCK_REALTIME,&tstart);
+   for (i = 0; i < nthreads; ++i) {
+      var[i].index = i;
+      var[i].points = npts;
+      pthread_create(&threads[i],NULL,fn,(void *) &var[i]);
+      }
+   for (i = 0; i < nthreads; ++i) {
+      pthread_join(threads[i],&status);
+      }
+   clock_gettime(CLOCK_REALTIME,&tend);
+   dt = (tend.tv_sec+tend.tv_nsec/1e9)-(tstart.tv_sec+tstart.tv_nsec/1e9);
+   mflops = nthreads*(npts*5.0/(dt*1e6));
+   printf("npts = %d, pi = %f\n",npts,pi);
+   printf("time = %f, estimated MFlops = %f\n",dt,mflops);
+   pthread_mutex_destroy(&mutex);
+   pthread_exit(NULL);
+   }

README.md

@@ -5,6 +5,7 @@
 |---|---|---|---|---|
 |71.46|[pi.html](https://pub.pages.cba.mit.edu/pi/JavaScript/pi.html)|JavaScript, 56 workers|Intel 2x E5-2680|Nov 19, 2018|
 |46.96|[mpipi.c](MPI/mpipi.c)|C, MPI<br>mpicc mpipi.c -o mpipi -O3 -ffast-math <br> mpirun -np 6 mpipi|Intel i7-8700T|Nov 17, 2018|
+|44.61|[threadpi.c](C/threadpi.c)|C, 6 threads<br>gcc threadpi.c -o threadpi -O3 -ffast-math -pthread|Intel i7-8700T|Dec 17, 2018|
 |16.16|[pi.html](https://pub.pages.cba.mit.edu/pi/JavaScript/pi.html)|JavaScript, 6 workers|Intel i7-8700T|Nov 17, 2018|
 |15.72|[clusterpi.js](Node/clusterpi.js)|Node, 6 workers|Intel i7-8700T|Dec 8, 2018|
 |9.371|[pi.c](C/pi.c)|C<br>gcc pi.c -o pi -lm -O3 -ffast-math|Intel i7-8700T|Nov 17, 2018|