include/opencascade/NCollection_Primes.hxx

0001 // Copyright (c) 2024 OPEN CASCADE SAS
0002 //
0003 // This file is part of Open CASCADE Technology software library.
0004 //
0005 // This library is free software; you can redistribute it and/or modify it under
0006 // the terms of the GNU Lesser General Public License version 2.1 as published
0007 // by the Free Software Foundation, with special exception defined in the file
0008 // OCCT_LGPL_EXCEPTION.txt. Consult the file LICENSE_LGPL_21.txt included in OCCT
0009 // distribution for complete text of the license and disclaimer of any warranty.
0010 //
0011 // Alternatively, this file may be used under the terms of Open CASCADE
0012 // commercial license or contractual agreement.
0013
0014 #ifndef _NCollection_Primes_HeaderFile
0015 #define _NCollection_Primes_HeaderFile
0016
0017 #include <Standard_Macro.hxx>
0018
0019 //! Namespace provides a collection of prime numbers.
0020 //!
0021 //! This namespace is used to store a collection of prime numbers that are used as
0022 //! consecutive steps for the size of an array of buckets in a map. The prime
0023 //! numbers are chosen to minimize the probability of having the same hash codes
0024 //! for different map items. The namespace also provides a method to find the next
0025 //! prime number greater than or equal to a given number.
0026 //!
0027 //! The following are Pierpont primes, prime numbers of the form 2^u * 3^v + 1:
0028 //! 101, 1009, 2003, 5003, 10007, 20011, 37003, 57037, 65003, 100019, 209953, 472393,
0029 //! 995329, 2359297, 4478977, 9437185, 17915905, 35831809, 71663617, 150994945,
0030 //! 301989889, 573308929, 1019215873, 2038431745
0031 namespace NCollection_Primes
0032 {
0033 //! Returns the next prime number greater than or equal to theN.
0034 Standard_EXPORT int NextPrimeForMap(const int theN);
0035 }; // namespace NCollection_Primes
0036
0037 #endif // _NCollection_Primes_HeaderFile