Data commit

Task/Gray-code/Limbo/gray-code.limbo

@@ -0,0 +1,50 @@
+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;
+}