| 1 | /*BHEADER**********************************************************************
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| 2 | * Copyright (c) 2008, Lawrence Livermore National Security, LLC.
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| 3 | * Produced at the Lawrence Livermore National Laboratory.
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| 4 | * This file is part of HYPRE. See file COPYRIGHT for details.
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| 5 | *
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| 6 | * HYPRE is free software; you can redistribute it and/or modify it under the
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| 7 | * terms of the GNU Lesser General Public License (as published by the Free
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| 8 | * Software Foundation) version 2.1 dated February 1999.
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| 9 | *
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| 10 | * $Revision: 2.4 $
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| 11 | ***********************************************************************EHEADER*/
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| 12 |
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| 13 |
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| 14 | /******************************************************************************
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| 15 | *
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| 16 | * This file contains routines that implement a pseudo-random number generator
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| 17 | * detailed in the following paper.
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| 18 | *
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| 19 | * @article{RNG_Park_Miller,
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| 20 | * author = {S. K. Park and K. W. Miller},
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| 21 | * title = {Random number generators: good ones are hard to find},
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| 22 | * journal = {Commun. ACM},
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| 23 | * volume = {31},
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| 24 | * number = {10},
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| 25 | * year = {1988},
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| 26 | * pages = {1192--1201},
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| 27 | * }
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| 28 | *
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| 29 | * This RNG has been shown to appear fairly random, it is a full period
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| 30 | * generating function (the sequence uses all of the values available to it up
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| 31 | * to 2147483647), and can be implemented on any architecture using 32-bit
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| 32 | * integers. The implementation in this file will not overflow for 32-bit
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| 33 | * arithmetic, which all modern computers should support.
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| 34 | *
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| 35 | * @author David Alber
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| 36 | * @date March 2005
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| 37 | *
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| 38 | *****************************************************************************/
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| 39 |
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| 40 | /*--------------------------------------------------------------------------
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| 41 | * Static variables
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| 42 | *--------------------------------------------------------------------------*/
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| 43 |
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| 44 | static int Seed = 13579;
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| 45 |
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| 46 | #define a 16807
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| 47 | #define m 2147483647
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| 48 | #define q 127773
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| 49 | #define r 2836
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| 50 |
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| 51 | /*--------------------------------------------------------------------------
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| 52 | * Initializes the pseudo-random number generator to a place in the sequence.
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| 53 | *
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| 54 | * @param seed an int containing the seed for the RNG.
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| 55 | *--------------------------------------------------------------------------*/
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| 56 |
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| 57 | void hypre_SeedRand( int seed )
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| 58 | {
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| 59 | Seed = seed;
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| 60 | }
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| 61 |
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| 62 | /*--------------------------------------------------------------------------
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| 63 | * Computes the next pseudo-random number in the sequence using the global
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| 64 | * variable Seed.
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| 65 | *
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| 66 | * @return a double containing the next number in the sequence divided by
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| 67 | * 2147483647 so that the numbers are in (0, 1].
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| 68 | *--------------------------------------------------------------------------*/
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| 69 |
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| 70 | double hypre_Rand()
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| 71 | {
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| 72 | int low, high, test;
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| 73 |
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| 74 | high = Seed / q;
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| 75 | low = Seed % q;
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| 76 | test = a * low - r * high;
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| 77 | if(test > 0)
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| 78 | {
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| 79 | Seed = test;
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| 80 | }
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| 81 | else
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| 82 | {
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| 83 | Seed = test + m;
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| 84 | }
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| 85 |
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| 86 | return ((double)(Seed) / m);
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| 87 | }
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