#include "harp1.h"

const dw = 8;         /* Data width */
const iw = dw << 1;   /* Internal data width */
const xw = 7;         /* Log horizontal size */
const yw = 7;         /* Log vertical size */
const aw = xw + yw;   /* Address width */
const ae = 1 << aw;   /* Number of elements in ram */

const null = 0 : dw;  /* Null element */

const threshold = 48;
const white = (1 << dw) - 1;
const black = 0;

#define LO(x) ((x) <- dw)  /* Lo word */
#define HI(x) ((x) \\ dw)  /* Hi word */

void main (chan (in)  STDIN          : dw,
	   chan (out) STDOUT         : dw,
	   eram img1[ae] = harp1lram : iw,
	   eram img2[ae] = harp1lram : 1)
{
    int x : xw;
    int y : yw;
    int p_0, p_1, p_2 : iw;

    int abs_diff() = abs(LO(p_2) - LO(p_0));
    int sum_abs()  = (false @ abs_diff() ) + (false @ HI(p_1));

    /* Differentiate in x direction */
    do {
	do par {
	    STDIN ? any;
	    p_0, p_1, p_2 = p_1, p_2, null @ STDIN;
	    img1[y @ x] = abs_diff() @ LO(p_1);
	    x = x + 1;
	} while (x != 0);
	y = y + 1;
    } while (y != 0);

    /* Differentiate and threshold in y direction */
    do {
	do par {
	    p_0, p_1, p_2 = p_1, p_2, img1[y @ x];
	    img2[y @ x] = (sum_abs() >= threshold ? 1 : 0);
	    y = y + 1;
	} while (y != 0);
	x = x + 1;
    } while (x != 0);

    /* Output */
    y = 2;
    do {
	x = 2;
	do par {
	    STDOUT ! (img2[y @ x] ? white : black);
	    x = x + 1;
	} while (x != 2);
	y = y + 1;
    } while (y != 2);
}