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#include <string.h>
#include "dns.h"
/** Rotate (shuffle) a block of fixed-length addresses.
\param s The array of memory to shuffle.
\param n The number of elements of the array.
\param shift The size of each element, expressed as a power-of-two
*/
void dns_rotate(unsigned char *s, unsigned int n, unsigned int shift)
{
unsigned int i;
unsigned int stride = 1 << shift;
unsigned char tmp[stride];
while (n > 1) {
i = dns_random(n);
--n;
memcpy(tmp, s + (i << shift), stride);
memcpy(s + (i << shift), s + (n << shift), stride);
memcpy(s + (n << shift), tmp, stride);
}
}
/** Rotate (shuffle) a block of IPv4 addresses. */
void dns_rotateipv4(ipv4addr* addrs, unsigned int n)
{
dns_rotate((unsigned char*)addrs, n, 2);
}
/** Rotate (shuffle) a block of IPv6 addresses. */
void dns_rotateipv6(ipv6addr* addrs, unsigned int n)
{
dns_rotate((unsigned char*)addrs, n, 4);
}
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