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StopFunc := function()
OnTaskCancellation(ReturnFail);
end;
SieveFactor := function(n)
local c, i, j, k, sieve, result;
n := AbsoluteValue(n);
if n <= 3 then
return [ n ];
fi;
k := Int(Sqrt(n*1.0));
sieve := BlistList([1..k], [1..k]);
result := [];
c := 0;
for i in [2..Length(sieve)] do
if n = 1 then
return result;
fi;
if sieve[i] then
while n mod i = 0 do
Add(result, i);
n := n / i;
od;
j := i * i;
if n = 1 or j >= n then
if n > 1 then
Add(result, n);
fi;
return result;
fi;
k := Int(Sqrt(n*1.0));
while j <= k do
PERIODIC_CHECK(1, StopFunc);
sieve[k] := false;
j := j + i;
od;
fi;
od;
if n > 1 then
Add(result, n);
fi;
return result;
end;
# Specialized faster version of RootInt(n,2) from integer.gi
SqrtNat := function(n)
local r, s;
if n <= 1 then
return n;
fi;
r := n;
s := 2^(QuoInt(LogInt(n, 2), 2)+1)-1;
while s < r do
r := s;
s := QuoInt(n + r*r, 2*r);
od;
if r * r = n then
return r;
else
return fail;
fi;
end;
FermatFactor2 := function(n)
local a, b, sqrt, i;
a := Int(Ceil(Sqrt(n*1.0)));
b := a * a - n;
i := 0;
while true do
PERIODIC_CHECK(1, StopFunc);
i := i + 1;
sqrt := SqrtNat(b);
if IsInt(sqrt) then
return [ a - sqrt, a + sqrt ];
fi;
a := a + 1;
b := a * a - n;
od;
end;
FermatFactorRec := function(n)
local result, f;
result := [];
if n = 1 then
return result;
fi;
f := FermatFactor2(n);
if f[1] = 1 then
Add(result, f[2]);
return result;
fi;
Append(result, FermatFactorRec(f[1]));
Append(result, FermatFactorRec(f[2]));
return result;
end;
FermatFactor := function(n)
local result;
if n <= 3 then
return [ n ];
fi;
result := [];
while n mod 2 = 0 do
Add(result, 2);
n := n / 2;
od;
Append(result, FermatFactorRec(n));
Sort(result);
return result;
end;
ParallelFactor := function(n)
local task, tasks, which, funcs;
funcs := [SieveFactor, FermatFactor];
tasks := List(funcs, f->RunTask(f, n));
which := WaitAnyTask(tasks);
for task in tasks do
# It is safe to cancel a completed task.
CancelTask(task);
WaitTask(task);
od;
Print(TaskResult(tasks[which]), " (", NAME_FUNC(funcs[which]), ")\n");
end;
Print("Factoring 2^44-1 -> \c");
ParallelFactor(2^44-1);
Print("Factoring 2^44+1 -> \c");
ParallelFactor(2^44+1);
[ Dauer der Verarbeitung: 0.3 Sekunden
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