proc gray_encode(word n) word:
    n >< (n >> 1)
corp

proc gray_decode(word n) word:
    word r;
    r := n;
    while
        n := n >> 1;
        n > 0
    do
        r := r >< n
    od;
    r
corp

proc main() void:
    word i, enc, dec;
    for i from 0 upto 31 do
        enc := gray_encode(i);
        dec := gray_decode(enc);
        writeln(i:2,     ": ",
                i:b:5,   " => ",
                enc:b:5, " => ",
                dec:b:5, " => ",
                dec:2)
    od
corp