September 2017 Update

Task/Gray-code/Bc/gray-code.bc

@@ -0,0 +1,46 @@
+scale = 0  /* to use integer division */
+
+/* encode Gray code */
+define e(i) {
+	auto h, r
+
+	if (i <= 0) return 0
+	h = i / 2
+	r = e(h) * 2                /* recurse */
+	if (h % 2 != i % 2) r += 1  /* xor low bits of h, i */
+	return r
+}
+
+/* decode Gray code */
+define d(i) {
+	auto h, r
+
+	if (i <= 0) return 0
+	h = d(i / 2)                /* recurse */
+	r = h * 2
+	if (h % 2 != i % 2) r += 1  /* xor low bits of h, i */
+	return r
+}
+
+
+/* print i as 5 binary digits */
+define p(i) {
+	auto d, d[]
+
+	for (d = 0; d <= 4; d++) {
+		d[d] = i % 2
+		i /= 2
+	}
+	for (d = 4; d >= 0; d--) {
+		if(d[d] == 0) "0"
+		if(d[d] == 1) "1"
+	}
+}
+
+for (i = 0; i < 32; i++) {
+	/* original */ t = p(i); " => "
+	/* encoded */ e = e(i); t = p(e); " => "
+	/* decoded */ d = d(e); t = p(d); "
+"
+}
+quit