#include<stdio.h>

#include<math.h>

#include<stdlib.h>

#include<string.h>

#include<linux/types.h>

#include<stdint.h>

#include<unistd.h>

#include<pthread.h>

#define ISON(n) ( grid[(n)/8] & (1<<((n)%8)) )

#define SETOFF(n) ( grid[(n)/8] &= ~(1<<((n)%8)) )

typedef struct targs {

uint64_t i;

uint64_t j;

} walkargs;

uint64_t max = 100;

int numthreads=0;

int maxthreads=4;

pthread_cond_t cond = PTHREAD_COND_INITIALIZER;

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

pthread_t *tid;

unsigned char *grid;

void *walkovergrid(void *args){

// walkargs *threadargs = (walkargs*)args;

uint64_t i = ((walkargs*)args)->i;

uint64_t j = ((walkargs*)args)->j;

for (j;j<max;j+=i) {

SETOFF(j);

// usleep(1000*500);

}

// printf("Finished deleting multiples of %u\n", i);

pthread_mutex_lock(&mutex);

numthreads--;

pthread_cond_signal(&cond);

pthread_mutex_unlock(&mutex);

pthread_exit(NULL);

}

int main(int argc, char* argv[]){

uint64_t i, j;

uint64_t ti=0;

walkargs *threadargs;

//printf("size of unsigned long long: %d\n", sizeof(unsigned long long));

//printf("size of uint64_t: %d\n", sizeof(uint64_t));

if ( argc > 1 ) {

max = strtoull(argv[1], NULL, 0);

}

grid = malloc(max/8);

memset(grid,0xaa,max/8); // 10101010 multiples of 2 are already set to 0

memset(grid,0b10101100,1);

threadargs = malloc(sqrt(max) * sizeof(walkargs));

tid = malloc(sqrt(max) * sizeof(pthread_t));

for (i=3; i<(uint64_t)sqrt(max); i++) {

if ( ISON(i) ) {

j = (uint64_t)pow(i,2);

SETOFF(j);

threadargs[ti].i=i;

threadargs[ti].j=j;

// printf("creating thread %d to remove multiples of %d\n", ti, i);

pthread_create(&tid[ti], NULL, walkovergrid, (void *)&threadargs[ti]);

numthreads++;

ti++;

pthread_mutex_lock(&mutex);

// printf("numthreads is %d and maxthreads is %d\n", numthreads, maxthreads);

while ( numthreads >= maxthreads ) {

pthread_cond_wait(&cond, &mutex);

}

pthread_mutex_unlock(&mutex);

}

}

// uncomment to print numbers

//int t=0;

//int rc;

//for(t=ti-maxthreads; t<ti; t++){

// printf("In main: joining thread #%d\n", t);

// rc = pthread_join(tid[ti-t], NULL);

// if (rc) { fprintf(stderr, "failed to join thread #%ld - %s\n",

// (long)t, strerror(rc));

// exit(EXIT_FAILURE);

// }

//}

//for (i=0;i<max;i++) {

// if ( ISON(i) ) {

// printf("%d\n", i);

// }

//}

free(grid);

pthread_exit(NULL);

}