102 lines
3.1 KiB
C
102 lines
3.1 KiB
C
/*BHEADER**********************************************************************
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* Copyright (c) 2007, Lawrence Livermore National Security, LLC.
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* Produced at the Lawrence Livermore National Laboratory.
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* Written by the HYPRE team. UCRL-CODE-222953.
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* All rights reserved.
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*
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* This file is part of HYPRE (see http://www.llnl.gov/CASC/hypre/).
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* Please see the COPYRIGHT_and_LICENSE file for the copyright notice,
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* disclaimer, contact information and the GNU Lesser General Public License.
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*
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* HYPRE is free software; you can redistribute it and/or modify it under the
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* terms of the GNU General Public License (as published by the Free Software
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* Foundation) version 2.1 dated February 1999.
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*
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* HYPRE is distributed in the hope that it will be useful, but WITHOUT ANY
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* WARRANTY; without even the IMPLIED WARRANTY OF MERCHANTABILITY or FITNESS
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* FOR A PARTICULAR PURPOSE. See the terms and conditions of the GNU General
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* Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program; if not, write to the Free Software Foundation,
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* Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*
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* $Revision$
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***********************************************************************EHEADER*/
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#include "_hypre_utilities.h"
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#include <math.h>
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/*--------------------------------------------------------------------------
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* hypre_DoubleQuickSplit
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* C version of the routine "qsplit" from SPARSKIT
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* Uses a quicksort-type algorithm to split data into
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* highest "NumberCut" values without completely sorting them.
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* Data is double precision data.
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*--------------------------------------------------------------------------*/
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int hypre_DoubleQuickSplit(double *values, int *indices,
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int list_length, int NumberKept )
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{
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int ierr = 0;
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double interchange_value;
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double abskey;
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int interchange_index;
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int first, last;
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int mid, j;
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int done;
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first = 0;
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last = list_length-1;
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if ( (NumberKept < first+1) || (NumberKept > last+1) )
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return( ierr );
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/* Loop until the "midpoint" is NumberKept */
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done = 0;
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for ( ; !done; )
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{
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mid = first;
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abskey = fabs( values[ mid ]);
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for( j = first+1; j <= last; j ++)
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{
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if( fabs( values[ j ]) > abskey )
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{
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mid ++;
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/* interchange values */
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interchange_value = values[ mid];
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interchange_index = indices[ mid];
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values[ mid] = values[ j];
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indices[ mid] = indices[ j];
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values[ j] = interchange_value;
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indices[ j] = interchange_index;
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}
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}
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/* interchange the first and mid value */
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interchange_value = values[ mid];
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interchange_index = indices[ mid];
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values[ mid] = values[ first];
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indices[ mid] = indices[ first];
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values[ first] = interchange_value;
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indices[ first] = interchange_index;
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if ( mid+1 == NumberKept )
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{
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done = 1;
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break;
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}
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if ( mid+1 > NumberKept )
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last = mid - 1;
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else
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first = mid + 1;
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}
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return ( ierr );
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}
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