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116 lines
2.5 KiB
C
116 lines
2.5 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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#pragma staticlocals(1);
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static char ReadUpperKey (void)
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/* Read a key from console, convert to upper case and return */
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{
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return toupper (cgetc ());
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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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unsigned Sec;
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unsigned Milli;
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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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/* Output a header */
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printf ("Sieve benchmark - calculating primes\n");
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printf ("between 2 and %u\n", COUNT);
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printf ("Please wait patiently ...\n");
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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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Sec = (unsigned) (Ticks / CLOCKS_PER_SEC);
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Milli = ((Ticks % CLOCKS_PER_SEC) * 1000) / CLOCKS_PER_SEC;
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/* Print the time used */
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printf ("Time used: %u.%03u seconds\n", Sec, Milli);
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printf ("Q to quit, any other key for list\n");
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/* Wait for a key and print the list if not 'Q' */
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if (ReadUpperKey () != 'Q') {
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/* Print the result */
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J = 0;
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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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if (++J == 23) {
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printf ("Q to quit, any other key continues\n");
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if (ReadUpperKey () == 'Q') {
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break;
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}
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J = 0;
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}
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}
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if (kbhit() && ReadUpperKey == 'Q') {
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break;
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}
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}
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}
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return EXIT_SUCCESS;
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}
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