www.pudn.com > src.rar > hash.c

#include  
#ifdef WIN32 
	#include  
	#include  
	#include "nids.h" 
#else 
	#include  
#endif 
#include  
#include  
#include  
#include  
 
#ifdef WIN32 
	long random(); 
	void srandom(unsigned int); 
#endif 
static u_char xor[12]; 
static u_char perm[12]; 
static void 
getrnd () 
{ 
  struct timeval s; 
  u_int *ptr; 
  int fd = open ("/dev/urandom", O_RDONLY); 
  if (fd > 0) 
    { 
      read (fd, xor, 12); 
      read (fd, perm, 12); 
      close (fd); 
      return; 
    } 
 
  gettimeofday (&s, 0); 
#ifdef WIN32 
  srandom (s.tv_usec); 
  ptr = (u_int *) xor; 
  *ptr = random (); 
  *(ptr + 1) = random (); 
  *(ptr + 2) = random (); 
  ptr = (u_int *) perm; 
  *ptr = random (); 
  *(ptr + 1) = random (); 
  *(ptr + 2) = random (); 
#else 
  srand (s.tv_usec); 
  ptr = (u_int *) xor; 
  *ptr = rand (); 
  *(ptr + 1) = rand (); 
  *(ptr + 2) = rand (); 
  ptr = (u_int *) perm; 
  *ptr = rand (); 
  *(ptr + 1) = rand (); 
  *(ptr + 2) = rand (); 
#endif 
 
} 
void 
init_hash () 
{ 
  int i, n, j; 
  int p[12]; 
  getrnd (); 
  for (i = 0; i < 12; i++) 
    p[i] = i; 
  for (i = 0; i < 12; i++) 
    { 
      n = perm[i] % (12 - i); 
      perm[i] = p[n]; 
      for (j = 0; j < 11 - n; j++) 
	p[n + j] = p[n + j + 1]; 
    } 
} 
 
u_int 
mkhash (u_int src, u_short sport, u_int dest, u_short dport) 
{ 
  u_int res = 0; 
  int i; 
  u_char data[12]; 
  *(u_int *) (data) = src; 
  *(u_int *) (data + 4) = dest; 
  *(u_short *) (data + 8) = sport; 
  *(u_short *) (data + 10) = dport; 
  for (i = 0; i < 12; i++) 
    res = ( (res << 8) + (data[perm[i]] ^ xor[i])) % 0xff100f; 
  return res; 
}