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#include <stdlib.h>
#include <string.h>
// returns list of primes up to limit; count stored in first element
extern unsigned long* primes(unsigned long limit)
{
unsigned long i = 2; // start sieving with 2
unsigned long pos, x;
char* numbers = (char*) malloc(limit*sizeof(char));
unsigned long* primes;
unsigned long primecount = 0;
memset(numbers, 1, limit);
numbers[0] = 0;
while(i*i <= limit)
{
// sieve current prime
x = i*i;
while(x <= limit)
{
numbers[x-1] = 0;
x += i;
}
// search next prime
pos = i;
while(++pos <= limit)
{
if(numbers[pos-1] == 1)
break;
}
i = pos;
}
// count primes
pos = 0;
while(++pos <= limit)
{
if(numbers[pos-1] == 1)
primecount++;
}
// create list of primes
primes = (unsigned long*) malloc((primecount+1)*sizeof(unsigned long)); // store count at first element
primes[0] = primecount;
pos = 0;
x = 1;
while(++pos <= limit)
{
if(numbers[pos-1] == 1)
primes[x++] = pos;
}
free(numbers);
return primes;
}
extern int isprime(unsigned long number, const unsigned long* primes)
{
unsigned long count = primes[0];
unsigned long pos = count/2 + 1;
unsigned long dist = pos/2 + 1;
unsigned long minpos = 0, maxpos = count;
if(number > primes[count] || number < 2)
return 0;
// some kind of binary search...
while(1)
{
if(number > primes[pos])
{
minpos = pos;
pos += dist;
}
else if(number < primes[pos])
{
maxpos = pos;
pos -= dist;
}
else
return 1;
dist /= 2;
if(dist == 1)
{
while(++minpos <= maxpos)
if(primes[minpos] == number)
return 1;
break;
}
}
return 0;
}
extern unsigned long phi(unsigned long n, unsigned long* primelist)
{
double product = (double) n;
unsigned long i;
//if(isprime(n, primelist))
// return n-1;
for(i=1; i<=primelist[0]; i++)
{
unsigned long p = primelist[i];
if(p > n)
break;
if(n % p != 0)
continue;
product *= (1 - 1.0/p);
}
return (unsigned long) product;
}
extern int ispermutation(unsigned long a, unsigned long b)
{
char digits1[10];
char digits2[10];
memset(digits1, 0, 10);
memset(digits2, 0, 10);
while(a > 0 && b > 0)
{
char d1 = a % 10;
char d2 = b % 10;
digits1[d1]++;
digits2[d2]++;
a /= 10;
b /= 10;
}
if(a > 0 || b > 0)
return 0;
if(memcmp(digits1, digits2, 10) == 0)
return 1;
return 0;
}
/*int main()
{
long* p = primes(10000);
//printf("%i\n", isprime(9973, p));
int i;
for(i=0; i<p[0]; i++)
printf("%d: %d\n", p[i+1], isprime(p[i+1], p));
free(p);
return 0;
}*/
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