/*
	Sieve of Eratosthenes benchmark from BYTE, Sep. '81, pg. 186.
	Compile by:
			A>cc1 sieve.c -e1000
	All variables have been made external to speed them up; other than
	that one change, the program is identical to the one used in the BYTE
	benchmark....while they got an execution time of 49.5 seconds and a
	size of 3932 bytes using v1.32 of the compiler,
			    ********
	v1.45 clocks in at  * 15.2 *  seconds with a size of 3718 bytes!
			    ********
*/

#define TRUE 1
#define FALSE 0
#define SIZE 8190
#define SIZEPL 8191

char flags[SIZEPL];
int i,prime,k,count,iter;

main()
{
	printf("Hit return to do 10 iterations: ");
	getchar();

	for (iter = 1; iter <= 10; iter++) {
		count = 0;
		for (i = 0; i <= SIZE; i++)
			flags[i] = TRUE;
		for (i = 0; i <= SIZE; i++) {
			if (flags[i]) {
				prime = i + i + 3;
				k = i + prime;
				while (k <= SIZE) {
					flags[k] = FALSE;
					k += prime;
				}
				count++;
			}
		}
	}
	printf("\7\n%d primes.\n",count);
}

.