/*************************************/¢/* Calculate all primes */¢/* up to a specific number. */¢/*************************************/¢¢#include <stdlib.h>¢#include <stdio.h>¢#include <ctype.h>¢#include <time.h>¢#include <conio.h>¢¢/*************************************/¢/* Data */¢/*************************************/¢¢/* Up to what number? */¢#define COUNT 8192¢¢/* Sqrt of COUNT */¢#define SQRT_COUNT 91¢¢static unsigned char Sieve[COUNT];¢¢/*************************************/¢/* Code */¢/*************************************/¢¢#pragma staticlocals(1);¢¢¢int main (void)¢{¢ /* Clock variable */¢ clock_t Ticks;¢¢ /* This is an example where */¢ /* register variables make sense */¢ register unsigned char* S;¢ register unsigned I;¢ register unsigned J;¢¢ /* Read the clock */¢ Ticks = clock();¢¢ /* Execute the sieve */¢ I = 2;¢ while (I < SQRT_COUNT)¢ {¢ if (Sieve[I] == 0)¢ {¢ /* Prime number - mark multiples */¢ S = &Sieve[J = I*2];¢ while (J < COUNT)¢ {¢ *S = 1;¢ S += I;¢ J += I;¢ }¢ }¢ ++I;¢ }¢¢ /* Calculate the time used */¢ Ticks = clock() - Ticks;¢¢ /* Print the time used */¢ printf ("Time used: %lu ticks\n", Ticks);¢ printf ("Press Q to quit, any other key for list\n");¢¢ /* Wait for a key */¢ /* and print the list if not 'Q' */¢ if (toupper (cgetc()) != 'Q')¢ {¢ /* Print the result */¢ for (I = 2; I < COUNT; ++I)¢ {¢ if (Sieve[I] == 0)¢ {¢ printf ("%4d\n", I);¢ }¢ if (kbhit() && toupper (cgetc()) == 'Q')¢ {¢ break;¢ }¢ }¢ }¢¢ return EXIT_SUCCESS;¢}¢
