Time for an 2014 update…

Task/Gray-code/D/gray-code-1.d

@@ -1,23 +1,22 @@
-import std.stdio;
-
-T enGray(T)(in T n) pure nothrow {
-    return n ^ (n >>> 1);
+uint grayEncode(in uint n) pure nothrow {
+    return n ^ (n >> 1);
 }
 
-T deGray(T)(in T n) pure nothrow {
-    enum T MSB = (cast(T)1) << (T.sizeof * 8 - 1);
-
-    auto res = (n & MSB) ;
-    foreach (bit; 1 .. T.sizeof * 8)
-        res += (n ^ (res >>> 1)) & (MSB >>> bit);
-    return res;
+uint grayDecode(uint n) pure nothrow {
+    auto p = n;
+    while (n >>= 1)
+        p ^= n;
+    return p;
 }
 
 void main() {
-    writeln("num  bits    encoded  decoded");
-    foreach (i; 0 .. 32) {
-        immutable encoded = enGray(i);
-        writefln("%2d: %5b ==> %5b : %2d",
-                 i, i, encoded, deGray(encoded));
+    import std.stdio;
+
+    " N     N2      enc     dec2 dec".writeln;
+    foreach (immutable n; 0 .. 32) {
+        immutable g = n.grayEncode;
+        immutable d = g.grayDecode;
+        writefln("%2d: %5b => %5b => %5b: %2d", n, n, g, d, d);
+        assert(d == n);
     }
 }