/*
 *	Based on Matt Segal (segal3@linkline.com)
 *               Rob James (rbjames@home.com)
 *               Chris Taylor (eagle19 at deja.com)
 *               E.J. Wilburn (zane@supernova.org)
 *      C++ code. 
 *      
 *      Modified by Marek
 *
 *	Compile: gcc -o primes primes.c -lm
 *               or
 *               gcc -o primes primes.c -DDOUBLE_OUTPUT -lm
 */

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define TRUE -1
#define FALSE 0

#define WHEEL_SIZE 48
#define WHEEL_MOD 210

const char *outfile_name = "found_primes.txt";

int wheel[WHEEL_SIZE] = {
	1, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67,
	71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 121, 127, 131, 
	137, 139, 143, 149, 151, 157, 163, 167, 169, 173, 179, 181, 187,
	191, 193, 197, 199, 209 };


int isprime(register long int);

int isprime(register long int value_to_check)
{
	register long int squareroot;
	register long int div;
	register long int mlt;
	register long int loop;

  	if(value_to_check < 3){
		if ((value_to_check == -1) || (value_to_check == 2))
      			return TRUE;
    		else
      			return FALSE;
  	}

  	if((value_to_check == 3) || (value_to_check == 5) || (value_to_check == 7)){
    		return TRUE;
	}

	if((value_to_check % 2 == 0) || (value_to_check % 3 == 0) || (value_to_check % 5 == 0) || (value_to_check % 7 == 0)){
    		return FALSE;
	}

  	if(value_to_check < 50){
    		return TRUE;
	}

  	squareroot = (long int) sqrt(value_to_check);
  	div = 0;

  	for(mlt = 0; div <= squareroot; mlt += WHEEL_MOD){
    		for(loop = (mlt > 0 ? 0: 1); loop < WHEEL_SIZE; loop++){
			if((div = wheel[loop] + mlt) > squareroot)
        			break;
      			if(value_to_check % div == 0)
				return FALSE;
    		}
	}

  	return TRUE;
}


int main(int argc, char **argv)
{
	register long int first_number;
	register long int last_number;
	register long int start;
	register int int_number;
	register long int long_number;
	long int counter = 0;
	FILE *outfile;

	if(argc!=2){
		fprintf(stderr, "Usage: %s last_value_to_check\n", argv[0]);
		exit(1);
	}

	first_number = 1L;
	last_number = atol(argv[1]);

	if(last_number <= 0){
		fprintf(stderr, "Error: bad parameter %s\n", argv[1]);
		exit(2);
	}

  	outfile = fopen(outfile_name,"w");

	if(!outfile){
		fprintf(stderr, "Error: unable to open output file %s, giving up...\n", outfile_name);
		exit(3);
	}

  	if(first_number < 4){
    		start = first_number;
	}
  	else{
    		start = first_number % 6;
    		switch (start){
      			case 0:
      			case 6:	start = first_number;
               			break;
      			default:
				start = ((first_number / 6) + (first_number < 0)? -1: 1) * 6;
    		}
  	}


	for(int_number = start; int_number < 4 && int_number < last_number; int_number++){
    		if (isprime(int_number)){
      			counter++;
#ifdef DOUBLE_OUTPUT
      			printf("%li\n", int_number);
#endif
      			fprintf(outfile, "%li\n", int_number);
    		}
	}

  	if(start < 6){
    		start = 6;
	}

  	for(long_number = start; long_number - 1 <= last_number ; long_number += 6){
    		if ((long_number - 1 >= first_number) && (long_number - 1 <= last_number) && isprime(long_number - 1)){
      			counter++;
#ifdef DOUBLE_OUTPUT
      			printf("%li\n", long_number - 1);
#endif
      			fprintf(outfile,"%li\n", long_number - 1);
    		}

    		if ((long_number + 1 >= first_number) && (long_number + 1 <= last_number) && isprime(long_number + 1)){
      			counter++;
#ifdef DOUBLE_OUTPUT
      			printf("%li\n", long_number + 1);
#endif
      			fprintf(outfile,"%li\n", long_number + 1);
    		}
  	}
  
  	fclose(outfile);

	printf("\n%i primes between 1 and %li written into output file %s\n\n", counter, last_number, outfile_name);

  	return 0;
}