Attempt at CM-5 "random and pleasing" pattern (rev. 2)

/* http://www.housedillon.com/?p=1272
 * Written by iskunk (Daniel Richard G.)
 * THIS FILE IS IN THE PUBLIC DOMAIN
 *
 * Program to emulate the CM-5's "random and pleasing" LED panel mode
 * (revision 2)
 */

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

#define NUM_ROWS 128

static uint16_t fn(uint16_t x)
{
    /* https://en.wikipedia.org/wiki/Linear_feedback_shift_register
     * Primitive polynomial: x^16 + x^12 + x^3 + x^1 + 1
     */
    return ((x >> 0) ^ (x >> 4) ^ (x >> 13) ^ (x >> 15)) & 1;
}

static void print_row(uint16_t x)
{
    uint16_t m;
    int pos;
    char v[17];

    for (m = 1 << 15, pos = 0; m != 0; m >>= 1, pos++)
        v[pos] = (x & m) ? 'O' : '-';

    v[16] = '\0';

    puts(v);
}

int main(void)
{
    uint16_t gen = 1;
    uint16_t rows[NUM_ROWS];
    int i;

    memset(rows, 0, sizeof(rows));

    for (;;)
    {
        /* ANSI sequence to clear terminal */
        fputs("\033[2J\033[1;1H", stdout);

        for (i = 0; i < NUM_ROWS; i++)
        {
            uint16_t gen_bit = fn(gen);
            uint16_t row_bit = ((gen >> 0) & (gen >> 1)) & 1;

            gen = (gen_bit << 15) | (gen >> 1);

            if (i & 4)
                rows[i] = (rows[i] << 1) | row_bit;
            else
                rows[i] = (row_bit << 15) | (rows[i] >> 1);

            print_row(rows[i]);
        }

        fflush(stdout);
        usleep(250000);
    }

    return 0;
}

/* EOF */