atl_icrefamax.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_icrefamax
(
   const int                  N,
   const float                * X,
   const int                  INCX
)
{
/*
 * Purpose
 * =======
 *
 * ATL_icrefamax  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 float *
 *         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( float [2] ),
 *         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 float             absxi, smax = ATL_sZERO, x0_r, x0_i, x1_r, x1_i,
                              x2_r, x2_i, x3_r, x3_i;
   float                      * StX;
   register int               imax = 0, i = 0, j;
   int                        incx2 = 2 * INCX,  nu;
   const int                  incX2 = 2 * incx2, incX3 = 3 * incx2,
                              incX4 = 4 * incx2;
/* ..
 * .. Executable Statements ..
 *
 */
   if( N > 0 )
   {
      if( ( nu = ( N >> 2 ) << 2 ) != 0 )
      {
         StX = (float *)X + nu * incx2;

         do
         {
            x0_r = (*X);       x2_r = X[incX2  ];
            x0_i = X[1];       x2_i = X[incX2+1];
            x1_r = X[incx2  ]; x3_r = X[incX3  ];
            x1_i = X[incx2+1]; x3_i = X[incX3+1];

            absxi = Msabs( x0_r ) + Msabs( x0_i );
            if( absxi > smax ) { imax = i; smax = absxi; }
            i    += 1;

            absxi = Msabs( x1_r ) + Msabs( x1_i );
            if( absxi > smax ) { imax = i; smax = absxi; }
            i    += 1;

            absxi = Msabs( x2_r ) + Msabs( x2_i );
            if( absxi > smax ) { imax = i; smax = absxi; }
            i    += 1;

            absxi = Msabs( x3_r ) + Msabs( x3_i );
            if( absxi > smax ) { imax = i; smax = absxi; }
            i    += 1;

            X  += incX4;

         } while( X != StX );
      }

      for( j = N - nu; j != 0; j-- )
      {
         x0_r  = (*X); x0_i = X[1];
         absxi = Msabs( x0_r ) + Msabs( x0_i );
         if( absxi > smax ) { imax = i; smax = absxi; }
         i    += 1;
         X  += incx2;
      }
   }
   return( imax );
/*
 * End of ATL_icrefamax
 */
}