--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/twice.c	Sat Feb 03 23:34:56 2018 +0900
@@ -0,0 +1,51 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <omp.h>
+#include <sys/time.h>
+
+int length = 1024;
+int cpu_num = 1;
+void init(int argc, const char* argv[]) {
+    for (int i = 1; argv[i]; ++i) {
+        if (strcmp(argv[i], "-cpu") == 0)
+            cpu_num = (int)atoi(argv[i+1]);
+        else if (strcmp(argv[i], "-l") == 0)
+            length = (int)atoi(argv[i+1]);
+    }
+}
+
+int main(int argc, const char* argv[])
+{
+    int n;
+    init(argc, argv);
+    omp_set_num_threads(cpu_num);
+    int *a;
+    a = (int *) malloc(sizeof(int) * length);
+    for (int i = 0; i < length; i++)
+    {
+        a[i] = i;
+    }
+
+    struct timeval tv;
+    gettimeofday(&tv, NULL);
+    double now = tv.tv_sec + (double)tv.tv_usec*1e-6;
+
+#pragma omp parallel for
+    for(int i = 0; i < length; i++)
+    {
+        a[i] = a[i] * 2;
+    }
+
+    gettimeofday(&tv, NULL);
+    printf("%0.6f\n", (tv.tv_sec+(double)tv.tv_usec*1e-6) - now);
+
+    for(int i = 0; i < length; i++)
+    {
+        if(a[i] != i*2) {
+	    printf("fail\n");
+	}
+    }
+
+    return 0;
+}