BigNum

Library for basic mathematical operations with preselected bit length.

Support: conversion from/into a string, compare, increase, decrease, addition, subtraction, multiplication, division, square root, exponentiation, bit shifts, ... https://github.com/DW0RKiN/BigNum/blob/master/bignum.h

The size of the number is 64*(1+ARRAY_128_BIT)*MAX_ARRAY_INDEX bits.

#include <stdio.h>
#include <stdint.h>
#include <time.h>
#include <sys/resource.h>

#define MAX_ARRAY_INDEX		2
#define ARRAY_128_BIT		1
#include "bignum.c"

double getcputime(void)        
{
	struct timeval tim;        
	struct rusage ru;        
	getrusage(RUSAGE_SELF, &ru);        
	tim=ru.ru_utime;        
	double t=(double)tim.tv_sec + (double)tim.tv_usec / 1000000.0;        
	tim=ru.ru_stime;        
	t+=(double)tim.tv_sec + (double)tim.tv_usec / 1000000.0;        
	return t;
}

void project_Euler_03(my_number * num)
{
	print_number ( stdout, "Project Euler problem 3\n\t", num, " =");	
	my_half i = 3;
	my_number stop, n, temp, prime, mod;
	char * s = " ";
	copy(&n,num);					// n = num;
	sqr(&stop, num);				// stop = sqrt(num);
	set_full(&prime, 2);				// prime = 2;
	while ( test_compare(&stop, &prime) >= 0 ) 
	{
		copy(&temp, &n);			// temp = n;
		div ( &temp, &prime, &mod );		// mod = temp % prime; temp /= prime;
		if ( test_zero ( &mod ) ) 		// if ( mod == 0 )
		{
			copy(&n, &temp );		// n = temp;
			sqr(&stop, &n);			// stop = sqrt(n);
			print_number (stdout, s, &prime, NULL);
			s = "*";

		} else 
		{
			if ( (i & 1) == 0 )		// 2,4 
			{
				add_half(&prime, i, -1);// 7,11,13,17,19,23,...+2,+4,+2,+4
				i = 6 - i;		// 2,4,2,4...
			} else				// 3,5,7 
			{
				prime.half[0] = i;
				i += 2;
				if ( i == 9 ) i = 4;
			}
		}
	}
	print_number (stdout, s, &n, "\n");
}

int main(int argc, char * argv[]) 
{
	if ( argc < 2 )
	{
		fprintf(stderr, "Prilis malo argumentu!\n");
		return 1;
	}
	my_number max;
	set_from_string(&max,argv[1]);			// max = argv[1]
	double start = getcputime();
	project_Euler_03(&max);
	printf("time: %f\n", getcputime() - start);
	return 0;
}

compile and run

dworkin@dworkin-Aspire-E1-572G:~/Programovani$ clang --version
clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

dworkin@dworkin-Aspire-E1-572G:~/Programovani$ clang -O3 -std=c99 -Wall euler03.c -o euler03 
dworkin@dworkin-Aspire-E1-572G:~/Programovani$ ./euler03 12345678901234567890123456
Project Euler problem 3
    12345678901234567890123456 = 2*2*2*2*2*2*3*17*71*218107*244251294564157
time: 2.644000

dworkin@dworkin-Aspire-E1-572G:~/Programovani$ gcc --version
gcc (Ubuntu 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

dworkin@dworkin-Aspire-E1-572G:~/Programovani$ gcc -O2 -std=c99 -Wall euler03.c -o euler03
dworkin@dworkin-Aspire-E1-572G:~/Programovani$ ./euler03 12345678901234567890123456
Project Euler problem 3
    12345678901234567890123456 = 2*2*2*2*2*2*3*17*71*218107*244251294564157
time: 7.444000

dworkin@dworkin-Aspire-E1-572G:~/Programovani$ gcc -O3 -std=c99 -Wall euler03.c -o euler03
dworkin@dworkin-Aspire-E1-572G:~/Programovani$ ./euler03 12345678901234567890123456
Project Euler problem 3
    12345678901234567890123456 = 2*2*2*2*2*2*3*17*71*218107*244251294564157
time: 1082.443000