RosettaCodeData/Task/Farey-sequence/XPL0/farey-sequence.xpl0

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proc Farey(N); \Show Farey sequence for N
\Translation of Python program on Wikipedia:
int N, A, B, C, D, K, T;
[A:= 0; B:= 1; C:= 1; D:= N;
Text(0, "0/1");
while C <= N do
[K:= (N+B)/D;
T:= C;
C:= K*C - A;
A:= T;
T:= D;
D:= K*D - B;
B:= T;
ChOut(0, ^ ); IntOut(0, A);
ChOut(0, ^/); IntOut(0, B);
];
];
func GCD(N, D); \Return the greatest common divisor of N and D
int N, D; \numerator and denominator
int R;
[if D > N then
[R:= D; D:= N; N:= R]; \swap D and N
while D > 0 do
[R:= rem(N/D);
N:= D;
D:= R;
];
return N;
]; \GCD
func Totient(N); \Return the totient of N
int N, Phi, M;
[Phi:= 0;
for M:= 1 to N do
if GCD(M, N) = 1 then Phi:= Phi+1;
return Phi;
];
func FareyLen(N); \Return length of Farey sequence for N
int N, Sum, M;
[Sum:= 1;
for M:= 1 to N do
Sum:= Sum + Totient(M);
return Sum;
];
int N;
[for N:= 1 to 11 do
[IntOut(0, N); Text(0, ": ");
Farey(N);
CrLf(0);
];
for N:= 1 to 10 do
[IntOut(0, N); Text(0, "00: ");
IntOut(0, FareyLen(N*100));
CrLf(0);
];
RlOut(0, 3.0 * sq(1000.0) / sq(3.141592654)); CrLf(0);
]