#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;
}