/* ex: set ts=2 et: */

/* by Ryan Flynn (pizza@parseerror.com) */
/* generate psuedo-randomness via cellular automata  */
/* (http://mathworld.wolfram.com/CellularAutomaton.html) */
/* constraints: minimal memory and CPU */

#include <stdio.h>
#include <stdint.h>

static uint8_t Rule = 89; /* rule #, previous bits used to decide future bits */
static uint16_t State = 0x6969; /* seed value, use whatever */

static void dumpbits(void)
{
  /* print bits to screen */
  uint16_t i = 1;
  do
    fputc('0' + !!(State & i), stdout);
  while (i <<= 1);
}

/* return a psuedo-random 16-bit value */
static uint16_t prand(void)
{
  /* advance State to next */
  uint16_t s = 0; /* next state */
  uint8_t i = 15;
  do {
    if (Rule & (1 << ((State >> i) & 0x7)))
      s |= 1 << i;
  } while (i--);
  State = s;
}

int main(void)
{
  int i = 32;
  uint16_t r;
  do {
    r = prand();
    printf("[%2u] ", i);
    dumpbits();
    printf("\n");
  } while (--i);
  return 0;
}