code real RlOut=48, Ln=54;      \intrinsic routines
string 0;                       \use zero-terminated strings

func StrLen(A);                 \Return number of characters in an ASCIIZ string
char A;
int  I;
for I:= 0, -1>>1-1 do
    if A(I) = 0 then return I;

func real Entropy(Str);         \Return Shannon entropy of string
char Str;
int  Len, I, Count(128);
real Sum, Prob;
[Len:= StrLen(Str);
for I:= 0 to 127 do Count(I):= 0;
for I:= 0 to Len-1 do           \count number of each character in string
    Count(Str(I)):= Count(Str(I)) + 1;
Sum:= 0.0;
for I:= 0 to 127 do
    if Count(I) # 0 then        \(avoid Ln(0.0) error)
        [Prob:= float(Count(I)) / float(Len);   \probability of char in string
        Sum:= Sum + Prob*Ln(Prob);
        ];
return -Sum/Ln(2.0);
];

RlOut(0, Entropy("1223334444"))