Created
October 5, 2011 01:12
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A prime number enumerator that uses wheel factorization.
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| public class WheelPrimeEnumerator : IEnumerator<int> | |
| { | |
| private readonly IEnumerator<int> _candidates = | |
| new WheelSequence(11, | |
| new BrokenRecord<int>( | |
| new[] { 4, 2, 4, 2, 4, 6, 2, 6 } | |
| ) | |
| ).GetEnumerator(); | |
| private readonly IPriorityQueue<NumberEnumerator> _pq = | |
| new IntervalHeap<NumberEnumerator>(); | |
| public int Current | |
| { | |
| get { return _candidates.Current; } | |
| } | |
| public bool MoveNext() | |
| { | |
| while (true) | |
| { | |
| _candidates.MoveNext(); | |
| int n = _candidates.Current; | |
| bool crossedOut = false; | |
| while (!crossedOut) | |
| { | |
| if (_pq.IsEmpty || n < _pq.FindMin().Current) | |
| { | |
| // There are no pending prime-multiples. | |
| // This means n is a prime! | |
| _pq.Add(new NumberEnumerator(n*n, n)); | |
| return true; | |
| } | |
| crossedOut = n == _pq.FindMin().Current; | |
| do | |
| { | |
| var temp = _pq.DeleteMin(); | |
| temp.MoveNext(); | |
| _pq.Add(temp); | |
| } while ((n > _pq.FindMin().Current) || | |
| (crossedOut && n == _pq.FindMin().Current)); | |
| } | |
| } | |
| } | |
| object IEnumerator.Current | |
| { | |
| get { return Current; } | |
| } | |
| public void Dispose() {} | |
| public void Reset() | |
| { | |
| throw new NotSupportedException(); | |
| } | |
| } |
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