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87 lines
1.7 KiB
C
87 lines
1.7 KiB
C
/*
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* Calculate all primes up to a specific number.
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*/
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#include <stdlib.h>
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#include <stdio.h>
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#include <ctype.h>
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#include <time.h>
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#include <conio.h>
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/*****************************************************************************/
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/* Data */
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/*****************************************************************************/
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#define COUNT 8192 /* Up to what number? */
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#define SQRT_COUNT 91 /* Sqrt of COUNT */
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static unsigned char Sieve[COUNT];
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/*****************************************************************************/
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/* Code */
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/*****************************************************************************/
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int main (void)
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{
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/* Clock variable */
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clock_t Ticks;
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/* This is an example where register variables make sense */
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register unsigned char* S;
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register unsigned I;
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register unsigned J;
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/* Read the clock */
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Ticks = clock();
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/* Execute the sieve */
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I = 2;
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while (I < SQRT_COUNT) {
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if (Sieve[I] == 0) {
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/* Prime number - mark multiples */
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S = &Sieve[J = I*2];
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while (J < COUNT) {
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*S = 1;
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S += I;
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J += I;
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}
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}
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++I;
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}
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/* Calculate the time used */
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Ticks = clock() - Ticks;
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/* Print the time used and wait for a key */
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printf ("Time used: %lu ticks\n", Ticks);
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printf ("Press Q to quit, any other key for list\n");
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if (toupper (cgetc()) == 'Q') {
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exit (EXIT_SUCCESS);
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}
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/* Print the result */
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for (I = 2; I < COUNT; ++I) {
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if (Sieve[I] == 0) {
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printf ("%4d\n", I);
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}
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if (kbhit() && toupper (cgetc()) == 'q') {
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break;
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}
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}
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return EXIT_SUCCESS;
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}
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