CM-5 'random and pleasing' LED code mode 7.

pleasing mode 7.c

/* 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 3)
 */

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

#define NUM_ROWS 32		/* unique rows */
#define NUM_ROWS_DISPLAYED 106	/* rows in front panel display */

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] = (row_bit << 15) | (rows[i] >> 1);
			else
				rows[i] = (rows[i] << 1) | row_bit;
		}

		for (i = 0; i < NUM_ROWS_DISPLAYED; i++)
			print_row(rows[i & 31]);

		fflush(stdout);
		usleep(250000);
	}

	return 0;
}

/* EOF */
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