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Ingy döt Net 2023-07-01 11:58:00 -04:00
parent 7387c8f97b
commit cb5bb5e222
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Task/Entropy/XPL0/entropy.xpl0 Normal file
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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"))