lapacke_dtz_trans.c

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******************************************************************************
* Contents: Native C interface to LAPACK utility function
* Author: Simon Märtens
*****************************************************************************/
 
#include "lapacke_utils.h"
 
/*****************************************************************************
  Converts input triangular matrix from row-major(C) to column-major(Fortran)
  layout or vice versa. The shape of the trapezoidal matrix is determined by
  the arguments `direct` and `uplo`. `Direct` chooses the diagonal which shall
  be considered and `uplo` tells us whether we use the upper or lower part of
  the matrix with respect to the chosen diagonal.
 
      Diagonals 'F' (front / forward) and 'B' (back / backward):
 
        A = ( F       )           A = ( F     B       )
            (    F    )               (    F     B    )
            ( B     F )               (       F     B )
            (    B    )
            (       B )
 
      direct = 'F', uplo = 'L':
 
        A = ( *       )           A = ( *             )
            ( *  *    )               ( *  *          )
            ( *  *  * )               ( *  *  *       )
            ( *  *  * )
            ( *  *  * )
 
      direct = 'F', uplo = 'U':
 
        A = ( *  *  * )           A = ( *  *  *  *  * )
            (    *  * )               (    *  *  *  * )
            (       * )               (       *  *  * )
            (         )
            (         )
 
      direct = 'B', uplo = 'L':
 
        A = (         )           A = ( *  *  *       )
            (         )               ( *  *  *  *    )
            ( *       )               ( *  *  *  *  * )
            ( *  *    )
            ( *  *  * )
 
      direct = 'B', uplo = 'U':
 
        A = ( *  *  * )           A = (       *  *  * )
            ( *  *  * )               (          *  * )
            ( *  *  * )               (             * )
            (    *  * )
            (       * )
 
*****************************************************************************/
 
void LAPACKE_dtz_trans( int matrix_layout, char direct, char uplo,
                        char diag, lapack_int m, lapack_int n,
                        const double *in, lapack_int ldin,
                        double *out, lapack_int ldout )
{
    lapack_logical colmaj, front, lower, unit;
 
    if( in == NULL || out == NULL ) return ;
 
    colmaj = ( matrix_layout == LAPACK_COL_MAJOR );
    front  = LAPACKE_lsame( direct, 'f' );
    lower  = LAPACKE_lsame( uplo, 'l' );
    unit   = LAPACKE_lsame( diag, 'u' );
 
    if( ( !colmaj && ( matrix_layout != LAPACK_ROW_MAJOR ) ) ||
        ( !front  && !LAPACKE_lsame( direct, 'b' ) ) ||
        ( !lower  && !LAPACKE_lsame( uplo, 'u' ) ) ||
        ( !unit   && !LAPACKE_lsame( diag, 'n' ) ) ) {
        /* Just exit if any of input parameters are wrong */
        return;
    }
 
    /* Initial offsets and sizes of triangular and rectangular parts */
    lapack_int tri_in_offset = 0;
    lapack_int tri_out_offset = 0;
    lapack_int tri_n = MIN(m,n);
    lapack_int rect_in_offset = -1;
    lapack_int rect_out_offset = -1;
    lapack_int rect_m = ( m > n ) ? m - n : m;
    lapack_int rect_n = ( n > m ) ? n - m : n;
 
    /* Fix offsets depending on the shape of the matrix */
    if( front ) {
        if( lower && m > n ) {
            rect_in_offset = tri_n * ( !colmaj ? ldin : 1 );
            rect_out_offset = tri_n * ( colmaj ? ldout : 1 );
        } else if( !lower && n > m ) {
            rect_in_offset = tri_n * ( colmaj ? ldin : 1 );
            rect_out_offset = tri_n * ( !colmaj ? ldout : 1 );
        }
    } else {
        if( m > n ) {
            tri_in_offset = rect_m * ( !colmaj ? ldin : 1 );
            tri_out_offset = rect_m * ( colmaj ? ldout : 1 );
            if( !lower ) {
                rect_in_offset = 0;
                rect_out_offset = 0;
            }
        } else if( n > m ) {
            tri_in_offset = rect_n * ( colmaj ? ldin : 1 );
            tri_out_offset = rect_n * ( !colmaj ? ldout : 1 );
            if( lower ) {
                rect_in_offset = 0;
                rect_out_offset = 0;
            }
        }
    }
 
    /* Copy & transpose rectangular part */
    if( rect_in_offset >= 0 && rect_out_offset >= 0 ) {
        LAPACKE_dge_trans( matrix_layout, rect_m, rect_n,
                           &in[rect_in_offset], ldin,
                           &out[rect_out_offset], ldout );
    }
 
    /* Copy & transpose triangular part */
    return LAPACKE_dtr_trans( matrix_layout, uplo, diag, tri_n,
                              &in[tri_in_offset], ldin,
                              &out[tri_out_offset], ldout );
}