36 lines
1.2 KiB
C++
36 lines
1.2 KiB
C++
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/* sieve.c */
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/* Eratosthenes Sieve Prime Number Program in C from Byte Jan 1983
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to compare the speed. */
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#include <stdio.h>
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#define TRUE 1
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#define FALSE 0
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#define SIZE 8190
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typedef int bool;
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char flags[SIZE+1];
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int main()
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{
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int i,k;
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int prime,count,iter;
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for (iter = 1; iter <= 10; iter++) { /* do program 10 times */
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count = 0; /* initialize prime counter */
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for (i = 0; i <= SIZE; i++) /* set all flags TRUE */
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flags[i] = TRUE;
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for (i = 0; i <= SIZE; i++) {
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if (flags[i]) { /* found a prime */
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prime = i + i + 3; /* twice index + 3 */
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for (k = i + prime; k <= SIZE; k += prime)
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flags[k] = FALSE; /* kill all multiples */
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count++; /* primes found */
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}
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}
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}
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printf("%d primes.\n",count); /*primes found in 10th pass */
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return 0;
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}
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