From 6053c6a590c833536b719c73a91b3d8d84b61fb6 Mon Sep 17 00:00:00 2001
From: Neil Gershenfeld <gersh@cba.mit.edu>
Date: Mon, 17 Dec 2018 21:41:23 -0500
Subject: [PATCH] wip
---
C/threadpi.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++
README.md | 1 +
2 files changed, 65 insertions(+)
create mode 100644 C/threadpi.c
diff --git a/C/threadpi.c b/C/threadpi.c
new file mode 100644
index 0000000..7af8afa
--- /dev/null
+++ b/C/threadpi.c
@@ -0,0 +1,64 @@
+/*
+* 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);
+ }
diff --git a/README.md b/README.md
index 997a1a4..996bc8d 100644
--- a/README.md
+++ b/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|
--
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