43 lines
1.4 KiB
C
43 lines
1.4 KiB
C
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// This version demonstrates use of the thread safe rand_r() function
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// for random number generation. It is not needed as there is only one
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// thread but shows the interface of the function.
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//
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// Sample program to estimate PI = 3.14159... by randomly generating
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// points in the positive quadrant and testing whether they are
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// distance <= 1.0 from the origin. The ratio of "hits" to tries is
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// an approximation for the area of the quarter circle with radius 1
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// so multiplying the ratio by 4 estimates pi.
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//
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// usage: picalc <num_samples>
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// num_samples: int, how many sample points to try, higher gets closer to pi
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#include <stdio.h>
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#include <stdlib.h>
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int main(int argc, char **argv) {
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if(argc < 2){
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printf("usage: %s <num_samples>\n",argv[0]);
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printf(" num_samples: int, how many sample points to try, higher gets closer to pi\n");
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return 1;
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}
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unsigned int rstate = 123456789; // seed state for random num generator
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int npoints = atoi(argv[1]);
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int total_hits=0;
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for (int i = 0; i < npoints; i++) {
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double x = ((double) rand_r(&rstate)) / ((double) RAND_MAX);
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double y = ((double) rand_r(&rstate)) / ((double) RAND_MAX);
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if (x*x + y*y <= 1.0){
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total_hits++;
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}
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}
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double pi_est = ((double)total_hits) / npoints * 4.0;
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printf("npoints: %8d\n",npoints);
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printf("hits: %8d\n",total_hits);
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printf("pi_est: %f\n",pi_est);
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return 0;
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}
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