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#include <unistd.h>
#include "dnsresolv.h"
#include "taia.h"
#include "uint_t.h"
/**
@file dns_random.c
@author djb
@ref ucspi-tcp
@brief random use of DNS resolvers given their IP
*/
static uint32 seed[32];
static uint32 in[12];
static uint32 out[8];
static int outleft = 0;
#define ROTATE(x, b) (((x) << (b)) | ((x) >> (32 - (b))))
#define MUSH(i, b) x = t[i] += (((x ^ seed[i]) + sum) ^ ROTATE(x, b))
static void surf(void)
{
uint32 t[12];
uint32 x;
uint32 sum = 0;
int r;
int i;
int loop;
for (i = 0; i < 12; ++i) t[i] = in[i] ^ seed[12 + i];
for (i = 0; i < 8; ++i) out[i] = seed[24 + i];
x = t[11];
for (loop = 0; loop < 2; ++loop) {
for (r = 0; r < 16; ++r) {
sum += 0x9e3779b9;
MUSH(0, 5);
MUSH(1, 7);
MUSH(2, 9);
MUSH(3, 13);
MUSH(4, 5);
MUSH(5, 7);
MUSH(6, 9);
MUSH(7, 13);
MUSH(8, 5);
MUSH(9, 7);
MUSH(10, 9);
MUSH(11, 13);
}
for (i = 0; i < 8; ++i) out[i] ^= t[i + 4];
}
}
void dns_random_init(const char data[128])
{
int i;
struct taia t;
char tpack[16];
for (i = 0; i < 32; ++i) uint32_unpack((char *)data + 4 * i, seed + i);
taia_now(&t);
taia_pack(tpack, &t);
for (i = 0; i < 4; ++i) uint32_unpack(tpack + 4 * i, in + 4 + i);
in[8] = getpid();
in[9] = getppid();
/* more space in 10 and 11, but this is probably enough */
}
unsigned int dns_random(unsigned int n)
{
if (!n) return 0;
if (!outleft) {
if (!++in[0])
if (!++in[1])
if (!++in[2]) ++in[3];
surf();
outleft = 8;
}
return out[--outleft] % n;
}
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