SQLite

static SQLITE_WSD struct sqlite3PrngType {
  unsigned char isInit;          /* True if initialized */
  unsigned char i, j;            /* State variables */
  unsigned char s[256];          /* State variables */
} sqlite3Prng;

/*
** Get a single 8-bit random value from the RC4 PRNG.  The Mutex
** must be held while executing this routine.
**
** Why not just use a library random generator like lrand48() for this?
** Because the OP_NewRowid opcode in the VDBE depends on having a very
** good source of random numbers.  The lrand48() library function may
** well be good enough.  But maybe not.  Or maybe lrand48() has some
** subtle problems on some systems that could cause problems.  It is hard
** to know.  To minimize the risk of problems due to bad lrand48()
** implementations, SQLite uses this random number generator based
** on RC4, which we know works very well.
**
** (Later):  Actually, OP_NewRowid does not depend on a good source of
** randomness any more.  But we will leave this code in all the same.
*/
static u8 randomByte(void){
  unsigned char t;


  /* The "wsdPrng" macro will resolve to the pseudo-random number generator
  ** state vector.  If writable static data is unsupported on the target,
  ** we have to locate the state vector at run-time.  In the more common
  ** case where writable static data is supported, wsdPrng can refer directly
  ** to the "sqlite3Prng" state vector declared above.
  */
#ifdef SQLITE_OMIT_WSD
  struct sqlite3PrngType *p = &GLOBAL(struct sqlite3PrngType, sqlite3Prng);
# define wsdPrng p[0]
#else
# define wsdPrng sqlite3Prng
#endif






  /* Initialize the state of the random number generator once,
  ** the first time this routine is called.  The seed value does
  ** not need to contain a lot of randomness since we are not
  ** trying to do secure encryption or anything like that...
  **
  ** Nothing in this file or anywhere else in SQLite does any kind of

      t = wsdPrng.s[wsdPrng.j];
      wsdPrng.s[wsdPrng.j] = wsdPrng.s[i];
      wsdPrng.s[i] = t;
    }
    wsdPrng.isInit = 1;
  }

  /* Generate and return single random byte
  */
  wsdPrng.i++;
  t = wsdPrng.s[wsdPrng.i];
  wsdPrng.j += t;
  wsdPrng.s[wsdPrng.i] = wsdPrng.s[wsdPrng.j];
  wsdPrng.s[wsdPrng.j] = t;
  t += wsdPrng.s[wsdPrng.i];
  return wsdPrng.s[t];
}

/*
** Return N random bytes.
*/
void sqlite3_randomness(int N, void *pBuf){
  unsigned char *zBuf = pBuf;
#if SQLITE_THREADSAFE
  sqlite3_mutex *mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_PRNG);
#endif
  sqlite3_mutex_enter(mutex);
  while( N-- ){
    *(zBuf++) = randomByte();
  }
  sqlite3_mutex_leave(mutex);
}

#ifndef SQLITE_OMIT_BUILTIN_TEST
/*
** For testing purposes, we sometimes want to preserve the state of