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/*
** Calculate all primes up to a specific number.
*/
#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>
#include <time.h>
#include <conio.h>
/* Workaround missing clock stuff */
#ifdef __APPLE2__
# define clock() 0
# define CLOCKS_PER_SEC 1
#endif
/*****************************************************************************/
/* Data */
/*****************************************************************************/
#define COUNT 16384 /* Up to what number? */
#define SQRT_COUNT 128 /* Sqrt of COUNT */
static unsigned char Sieve[COUNT];
/*****************************************************************************/
/* Code */
/*****************************************************************************/
#pragma static-locals(1);
static char ReadUpperKey (void)
/* Read a key from console, convert to upper case and return */
{
return toupper (cgetc ());
}
int main (void)
{
/* Clock variable */
clock_t Ticks;
unsigned Sec;
unsigned Milli;
/* This is an example where register variables make sense */
register unsigned char* S;
register unsigned I;
register unsigned J;
/* Output a header */
printf ("Sieve benchmark - calculating primes\n");
printf ("between 2 and %u\n", COUNT);
printf ("Please wait patiently ...\n");
/* Read the clock */
Ticks = clock();
/* Execute the sieve */
I = 2;
while (I < SQRT_COUNT) {
if (Sieve[I] == 0) {
/* Prime number - mark multiples */
J = I*2;
S = &Sieve[J];
while (J < COUNT) {
*S = 1;
S += I;
J += I;
}
}
++I;
}
/* Calculate the time used */
Ticks = clock() - Ticks;
Sec = (unsigned) (Ticks / CLOCKS_PER_SEC);
Milli = ((Ticks % CLOCKS_PER_SEC) * 1000) / CLOCKS_PER_SEC;
/* Print the time used */
printf ("Time used: %u.%03u seconds\n", Sec, Milli);
printf ("Q to quit, any other key for list\n");
/* Wait for a key and print the list if not 'Q' */
if (ReadUpperKey () != 'Q') {
/* Print the result */
J = 0;
for (I = 2; I < COUNT; ++I) {
if (Sieve[I] == 0) {
printf ("%4d\n", I);
if (++J == 23) {
printf ("Q to quit, any other key continues\n");
if (ReadUpperKey () == 'Q') {
break;
}
J = 0;
}
}
if (kbhit() && ReadUpperKey () == 'Q') {
break;
}
}
}
return EXIT_SUCCESS;
}
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