dasum.f

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*> \brief \b DASUM
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at 
*            http://www.netlib.org/lapack/explore-html/ 
*
*  Definition:
*  ===========
*
*       DOUBLE PRECISION FUNCTION DASUM(N,DX,INCX)
* 
*       .. Scalar Arguments ..
*       INTEGER INCX,N
*       ..
*       .. Array Arguments ..
*       DOUBLE PRECISION DX(*)
*       ..
*  
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*>    DASUM takes the sum of the absolute values.
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee 
*> \author Univ. of California Berkeley 
*> \author Univ. of Colorado Denver 
*> \author NAG Ltd. 
*
*> \date November 2011
*
*> \ingroup double_blas_level1
*
*> \par Further Details:
*  =====================
*>
*> \verbatim
*>
*>     jack dongarra, linpack, 3/11/78.
*>     modified 3/93 to return if incx .le. 0.
*>     modified 12/3/93, array(1) declarations changed to array(*)
*> \endverbatim
*>
*  =====================================================================
      DOUBLE PRECISION FUNCTION dasum(N,DX,INCX)
*
*  -- Reference BLAS level1 routine (version 3.4.0) --
*  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*     November 2011
*
*     .. Scalar Arguments ..
      INTEGER INCX,N
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION DX(*)
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      DOUBLE PRECISION DTEMP
      INTEGER I,M,MP1,NINCX
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC dabs,mod
*     ..
      dasum = 0.0d0
      dtemp = 0.0d0
      IF (n.LE.0 .OR. incx.LE.0) RETURN
      IF (incx.EQ.1) THEN
*        code for increment equal to 1
*
*
*        clean-up loop
*
         m = mod(n,6)
         IF (m.NE.0) THEN
            DO i = 1,m
               dtemp = dtemp + dabs(dx(i))
            END DO
            IF (n.LT.6) THEN
               dasum = dtemp
               RETURN
            END IF
         END IF
         mp1 = m + 1
         DO i = mp1,n,6
            dtemp = dtemp + dabs(dx(i)) + dabs(dx(i+1)) +
     $              dabs(dx(i+2)) + dabs(dx(i+3)) +
     $              dabs(dx(i+4)) + dabs(dx(i+5))
         END DO
      ELSE
*
*        code for increment not equal to 1
*
         nincx = n*incx
         DO i = 1,nincx,incx
            dtemp = dtemp + dabs(dx(i))
         END DO
      END IF
      dasum = dtemp
      RETURN
      END