File: template_lapack_rscl.h

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/* Ergo, version 3.8.2, a program for linear scaling electronic structure
 * calculations.
 * Copyright (C) 2023 Elias Rudberg, Emanuel H. Rubensson, Pawel Salek,
 * and Anastasia Kruchinina.
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 * 
 * Primary academic reference:
 * Ergo: An open-source program for linear-scaling electronic structure
 * calculations,
 * Elias Rudberg, Emanuel H. Rubensson, Pawel Salek, and Anastasia
 * Kruchinina,
 * SoftwareX 7, 107 (2018),
 * <http://dx.doi.org/10.1016/j.softx.2018.03.005>
 * 
 * For further information about Ergo, see <http://www.ergoscf.org>.
 */
 
 /* This file belongs to the template_lapack part of the Ergo source 
  * code. The source files in the template_lapack directory are modified
  * versions of files originally distributed as CLAPACK, see the
  * Copyright/license notice in the file template_lapack/COPYING.
  */
 

#ifndef TEMPLATE_LAPACK_RSCL_HEADER
#define TEMPLATE_LAPACK_RSCL_HEADER


template<class Treal>
int template_lapack_rscl(const integer *n, const Treal *sa, Treal *sx, 
	const integer *incx)
{
/*  -- LAPACK auxiliary routine (version 3.0) --   
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
       Courant Institute, Argonne National Lab, and Rice University   
       September 30, 1994   


    Purpose   
    =======   

    DRSCL multiplies an n-element real vector x by the real scalar 1/a.   
    This is done without overflow or underflow as long as   
    the final result x/a does not overflow or underflow.   

    Arguments   
    =========   

    N       (input) INTEGER   
            The number of components of the vector x.   

    SA      (input) DOUBLE PRECISION   
            The scalar a which is used to divide each component of x.   
            SA must be >= 0, or the subroutine will divide by zero.   

    SX      (input/output) DOUBLE PRECISION array, dimension   
                           (1+(N-1)*abs(INCX))   
            The n-element vector x.   

    INCX    (input) INTEGER   
            The increment between successive values of the vector SX.   
            > 0:  SX(1) = X(1) and SX(1+(i-1)*INCX) = x(i),     1< i<= n   

   =====================================================================   


       Quick return if possible   

       Parameter adjustments */
     Treal cden;
     logical done;
     Treal cnum, cden1, cnum1;
     Treal bignum, smlnum, mul;

    --sx;

    /* Function Body */
    if (*n <= 0) {
	return 0;
    }

/*     Get machine parameters */

    smlnum = template_lapack_lamch("S", (Treal)0);
    bignum = 1. / smlnum;
    template_lapack_labad(&smlnum, &bignum);

/*     Initialize the denominator to SA and the numerator to 1. */

    cden = *sa;
    cnum = 1.;

L10:
    cden1 = cden * smlnum;
    cnum1 = cnum / bignum;
    if (absMACRO(cden1) > absMACRO(cnum) && cnum != 0.) {

/*        Pre-multiply X by SMLNUM if CDEN is large compared to CNUM. */

	mul = smlnum;
	done = FALSE_;
	cden = cden1;
    } else if (absMACRO(cnum1) > absMACRO(cden)) {

/*        Pre-multiply X by BIGNUM if CDEN is small compared to CNUM. */

	mul = bignum;
	done = FALSE_;
	cnum = cnum1;
    } else {

/*        Multiply X by CNUM / CDEN and return. */

	mul = cnum / cden;
	done = TRUE_;
    }

/*     Scale the vector X by MUL */

    dscal_(n, &mul, &sx[1], incx);

    if (! done) {
	goto L10;
    }

    return 0;

/*     End of DRSCL */

} /* drscl_ */

#endif