40 lines
973 B
C
40 lines
973 B
C
#include <stdio.h>
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#include <omp.h>
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#include <sys/time.h>
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long long num_steps = 1000000000;
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double step;
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int main(int argc, char* argv[])
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{
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struct timeval TimeStampStart, TimeStampStop;
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double ExeTime;
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double x, pi, sum=0.0;
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int i;
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step = 1./(double)num_steps;
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gettimeofday(&TimeStampStart, NULL);
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// 并行计算PI，使用OpenMP的reduction合并部分和
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#pragma omp parallel private(x) reduction(+:sum)
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{
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#pragma omp for
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for (i=0; i<num_steps; i++)
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{
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x = (i + .5)*step;
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sum = sum + 4.0/(1.+ x*x);
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}
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}
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pi = sum*step;
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gettimeofday(&TimeStampStop, NULL);
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ExeTime = (double)(TimeStampStop.tv_sec - TimeStampStart.tv_sec) +
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(double)(TimeStampStop.tv_usec - TimeStampStart.tv_usec) * 1e-6;
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printf("The value of PI is %15.12f\n",pi);
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printf("The time to calculate PI was %f seconds\n", (ExeTime));
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return 0;
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}
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