implement Gray;

include "sys.m"; sys: Sys;
	print: import sys;
include "draw.m";

Gray: module {
	init: fn(nil: ref Draw->Context, args: list of string);
	# Export gray and grayinv so that this module can be used as either a
	# standalone program or as a library:
	gray: fn(n: int): int;
	grayinv: fn(n: int): int;
};

init(nil: ref Draw->Context, args: list of string)
{
	sys = load Sys Sys->PATH;
	for(i := 0; i < 32; i++) {
		g := gray(i);
		f := grayinv(g);
		print("%2d  %5s  %2d  %5s  %5s  %2d\n", i, binstr(i), g, binstr(g), binstr(f), f);
	}
}

gray(n: int): int
{
	return n ^ (n >> 1);
}

grayinv(n: int): int
{
	r := 0;
	while(n) {
		r ^= n;
		n >>= 1;
	}
	return r;
}

binstr(n: int): string
{
	if(!n)
		return "0";
	s := "";
	while(n) {
		s = (string (n&1)) + s;
		n >>= 1;
	}
	return s;
}