atl_idrefamax.c

来自「基于Blas CLapck的.用过的人知道是干啥的」· C语言 代码 · 共 147 行

/* ---------------------------------------------------------------------
 *
 * -- Automatically Tuned Linear Algebra Software (ATLAS)
 *    (C) Copyright 2000 All Rights Reserved
 *
 * -- ATLAS routine -- Version 3.2 -- December 25, 2000
 *
 * Author         : Antoine P. Petitet
 * Originally developed at the University of Tennessee,
 * Innovative Computing Laboratory, Knoxville TN, 37996-1301, USA.
 *
 * ---------------------------------------------------------------------
 *
 * -- Copyright notice and Licensing terms:
 *
 *  Redistribution  and  use in  source and binary forms, with or without
 *  modification, are  permitted provided  that the following  conditions
 *  are met:
 *
 * 1. Redistributions  of  source  code  must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce  the above copyright
 *    notice,  this list of conditions, and the  following disclaimer in
 *    the documentation and/or other materials provided with the distri-
 *    bution.
 * 3. The name of the University,  the ATLAS group,  or the names of its
 *    contributors  may not be used to endorse or promote products deri-
 *    ved from this software without specific written permission.
 *
 * -- Disclaimer:
 *
 * THIS  SOFTWARE  IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,  INCLUDING,  BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE UNIVERSITY
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,  INDIRECT, INCIDENTAL, SPE-
 * CIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
 * TO,  PROCUREMENT  OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
 * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEO-
 * RY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT  (IN-
 * CLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * ---------------------------------------------------------------------
 */
/*
 * Include files
 */
#include "atlas_refmisc.h"
#include "atlas_reflevel1.h"

int ATL_idrefamax
(
   const int                  N,
   const double               * X,
   const int                  INCX
)
{
/*
 * Purpose
 * =======
 *
 * ATL_idrefamax  returns the index in an n-vector x of the first element
 * having maximum absolute value.
 *
 * Arguments
 * =========
 *
 * N       (input)                       const int
 *         On entry, N specifies the length of the vector x. N  must  be
 *         at least zero. Unchanged on exit.
 *
 * X       (input)                       const double *
 *         On entry,  X  points to the  first entry to be accessed of an
 *         incremented array of size equal to or greater than
 *            ( 1 + ( n - 1 ) * abs( INCX ) ) * sizeof(   double  ),
 *         that contains the vector x. Unchanged on exit.
 *
 * INCX    (input)                       const int
 *         On entry, INCX specifies the increment for the elements of X.
 *         INCX must not be zero. Unchanged on exit.
 *
 * ---------------------------------------------------------------------
 */
/*
 * .. Local Variables ..
 */
   register double            absxi, smax = ATL_dZERO, x0, x1, x2, x3,
                              x4, x5, x6, x7;
   double                     * StX;
   register int               imax = 0, i = 0, j;
   int                        nu;
   const int                  incX2 = 2 * INCX, incX3 = 3 * INCX,
                              incX4 = 4 * INCX, incX5 = 5 * INCX,
                              incX6 = 6 * INCX, incX7 = 7 * INCX,
                              incX8 = 8 * INCX;
/* ..
 * .. Executable Statements ..
 *
 */
   if( N > 0 )
   {
      if( ( nu = ( N >> 3 ) << 3 ) != 0 )
      {
         StX = (double *)X + nu * INCX;

         do
         {
            x0 = (*X);     x4 = X[incX4]; x1 = X[INCX ]; x5 = X[incX5];
            x2 = X[incX2]; x6 = X[incX6]; x3 = X[incX3]; x7 = X[incX7];

            absxi = Mdabs( x0 ); if( absxi > smax ) { imax = i; smax = absxi; }
            i    += 1;
            absxi = Mdabs( x1 ); if( absxi > smax ) { imax = i; smax = absxi; }
            i    += 1;
            absxi = Mdabs( x2 ); if( absxi > smax ) { imax = i; smax = absxi; }
            i    += 1;
            absxi = Mdabs( x3 ); if( absxi > smax ) { imax = i; smax = absxi; }
            i    += 1;
            absxi = Mdabs( x4 ); if( absxi > smax ) { imax = i; smax = absxi; }
            i    += 1;
            absxi = Mdabs( x5 ); if( absxi > smax ) { imax = i; smax = absxi; }
            i    += 1;
            absxi = Mdabs( x6 ); if( absxi > smax ) { imax = i; smax = absxi; }
            i    += 1;
            absxi = Mdabs( x7 ); if( absxi > smax ) { imax = i; smax = absxi; }
            i    += 1;

            X    += incX8;

         } while( X != StX );
      }

      for( j = N - nu; j != 0; j-- )
      {
         x0    = (*X);
         absxi = Mdabs( x0 ); if( absxi > smax ) { imax = i; smax = absxi; }
         i    += 1;
         X    += INCX;
      }
   }
   return( imax );
/*
 * End of ATL_idrefamax
 */
}