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/// <summary>
/// A class for sequentially reading prime numbers from the file specified in PrimeNumberGenerator.PrimeDatabaseFileName
/// </summary>
/// <remarks>
/// Usage:
///
/// static void Main(string[] args)
/// {
/// PrimeNumberReader pnr = new PrimeNumberReader()
/// pnr.BeginGetNextPrime();
/// ...
/// pnr.GetNextPrime();
/// ...
/// pnr.EndGetNextPrime();
/// }
/// </remarks>
public class PrimeNumberReader
{
private BinaryReader file = null;
/// <summary>
/// Prepare for reading prime numbers from file
/// </summary>
public void BeginGetNextPrime()
{
if (File.Exists(PrimeNumberGenerator.PrimeDatabaseFileName))
{
file = new BinaryReader(new FileStream(PrimeNumberGenerator.PrimeDatabaseFileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite));
}
else
{
throw new PrimeNumbersNotCalculatedException();
}
}
/// <summary>
/// End reading prime numbers from file
/// </summary>
public void EndGetNextPrime()
{
file.Close();
file = null;
}
/// <summary>
/// Get the next prime number in file
/// </summary>
/// <returns>The next prime number found in file at current position</returns>
public long GetNextPrime()
{
if (file == null)
{
throw new InvalidOperationException("Call BeginGetNextPrime() first");
}
if (file.BaseStream.Position < file.BaseStream.Length)
{
return file.ReadInt64();
}
else
{
throw new PrimeNumbersNotCalculatedException();
}
}
/// <summary>
/// Get the next prime number in file greater than a specified number
/// </summary>
/// <param name="Number">The prime has to be greater than this number</param>
/// <returns>The next prime greater than the specified number</returns>
public long GetNextPrime( long Number )
{
if (file == null)
{
throw new InvalidOperationException("Call BeginGetNextPrime() first");
}
long intern = 0;
while ((file.BaseStream.Position < file.BaseStream.Length) && (intern < Number))
{
intern = file.ReadInt64();
}
if (intern > Number)
{
return intern;
}
else
{
throw new PrimeNumbersNotCalculatedException();
}
}
}
/// <summary>
/// This exception is thrown if a prime number is needed that is greater
/// than any by now calculated prime numbers => calculate more
/// </summary>
public class PrimeNumbersNotCalculatedException : System.Exception
{
public long GreatestPrimeByNow
{
get
{
return PrimeNumberGenerator.GreatestKnownPrimeNumber;
}
}
public PrimeNumbersNotCalculatedException() : base(){}
}
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