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/*

 * lfsr128.c -- a linear feedback shift register with 128 bits

 *              (actually constructed from 4 instances of a 32-bit lfsr)

 */

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

int main(void) {

  unsigned int startState[4] = {

    0xC70337DB,

    0x7F4D514F,

    0x75377599,

    0x7D5937A3

  };

  /* taps at 32 31 29 1 */

  unsigned int taps = 0xD0000001;

  unsigned int lfsr[4];

  int i, n;

  for (i = 0; i < 4; i++) {

    lfsr[i] = startState[i];

  }

  for (n = 0; n < 530; n++) {

    /*

     * The trigger condition in the actual hardware test will be set

     * to lfsr[0]==0x7119C0CD, which is reached at n==10. Therefore

     * we print out n-10 instead of n to get identical index numbers.

     */

    printf("%03d:  ", n - 10);

    for (i = 0; i < 4; i++) {

      printf("%02X  ", (lfsr[i] >> 24) & 0xFF);

      printf("%02X  ", (lfsr[i] >> 16) & 0xFF);

      printf("%02X  ", (lfsr[i] >>  8) & 0xFF);

      printf("%02X  ", (lfsr[i] >>  0) & 0xFF);

    }

    printf("\n");

    for (i = 0; i < 4; i++) {

      if ((lfsr[i] & 1) == 0) {

        lfsr[i] = lfsr[i] >> 1;

      } else {

        lfsr[i] = (lfsr[i] >> 1) ^ taps;

      }

    }

  }

  return 0;

}