完成并修改正确必做题

exp1/psum64.c

@@ -0,0 +1,79 @@
+/*任务4(必做）：编译、测试和运行示例程序psum64.c
+1）测量线程数为1、2、4、8、16时程序的执行时间，计算加速比和效率，并做出解释。
+2）改写该程序psum64.c,保存为task64.c，实现计算02+12+… +(n-1)2功能。
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <semaphore.h>
+#include <time.h>
+
+#define MAXTHREADS 16
+
+void *sum(void *vargp);
+
+unsigned long long psum64[MAXTHREADS];
+unsigned long long nelems_per_thread;
+
+int main(int argc, char **argv)
+{
+    unsigned long long i,nelems,log_nelems,nthreads,result = 0;
+    pthread_t tid[MAXTHREADS];
+    int myid[MAXTHREADS];
+
+    if(argc != 3)
+    {
+        printf("Usage: %s <nthreads> <log_nelems>\n",argv[0]);
+        exit(0);
+    }
+    nthreads = atoi(argv[1]);
+    log_nelems = atoi(argv[2]);
+    nelems = (1LL << log_nelems);
+    nelems_per_thread = nelems / nthreads;
+    
+    for ( i = 0; i < nthreads; i++)
+    {
+        myid[i] = i;
+        pthread_create(&tid[i],NULL,sum,&myid[i]);
+    }
+
+    for ( i = 0; i < nthreads; i++)
+    {
+        pthread_join(tid[i],NULL);
+    }
+
+    for ( i = 0; i < nthreads; i++)
+    {
+        result += psum64[i];
+    }
+    
+    if (result == (nelems*(nelems-1))/2)
+    {
+        printf("Correct result: %ld\n",result);
+    }
+    else
+    {
+        printf("Wrong result: %ld\n",result);
+    }
+
+    exit(0);
+}
+
+
+
+void *sum(void *vargp)
+{
+    int myid = *((int *)vargp);
+    unsigned long long begin = myid * nelems_per_thread;
+    unsigned long long end = begin + nelems_per_thread;
+    unsigned long long i,lsum=0;
+
+    for (i = begin; i < end; i++)
+    {
+        lsum += i;
+    }
+
+    psum64[myid] = lsum;
+    return NULL;
+}