srscl.f

          SUBROUTINE SRSCL( N, SA, SX, INCX )
    *
    *  -- LAPACK auxiliary routine (version 3.1) --
    *     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
    *     November 2006
    *
    *     .. Scalar Arguments ..
          INTEGER            INCX, N
          REAL               SA
    *     ..
    *     .. Array Arguments ..
          REAL               SX( * )
    *     ..
    *
    *  Purpose
    *  =======
    *
    *  SRSCL 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) REAL
    *          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) REAL 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
    *
    * =====================================================================
    *
    *     .. Parameters ..
          REAL               ONE, ZERO
          PARAMETER          ( ONE = 1.0E+0, ZERO = 0.0E+0 )
    *     ..
    *     .. Local Scalars ..
          LOGICAL            DONE
          REAL               BIGNUM, CDEN, CDEN1, CNUM, CNUM1, MUL, SMLNUM
    *     ..
    *     .. External Functions ..
          REAL               SLAMCH
          EXTERNAL           SLAMCH
    *     ..
    *     .. External Subroutines ..
          EXTERNAL           SLABAD, SSCAL
    *     ..
    *     .. Intrinsic Functions ..
          INTRINSIC          ABS
    *     ..
    *     .. Executable Statements ..
    *
    *     Quick return if possible
    *
          IF( N.LE.0 )
         $   RETURN
    *
    *     Get machine parameters
    *
          SMLNUM = SLAMCH( 'S' )
          BIGNUM = ONE / SMLNUM
          CALL SLABAD( SMLNUM, BIGNUM )
    *
    *     Initialize the denominator to SA and the numerator to 1.
    *
          CDEN = SA
          CNUM = ONE
    *
       10 CONTINUE
          CDEN1 = CDEN*SMLNUM
          CNUM1 = CNUM / BIGNUM
          IF( ABS( CDEN1 ).GT.ABS( CNUM ) .AND. CNUM.NE.ZERO ) THEN
    *
    *        Pre-multiply X by SMLNUM if CDEN is large compared to CNUM.
    *
             MUL = SMLNUM
             DONE = .FALSE.
             CDEN = CDEN1
          ELSE IF( ABS( CNUM1 ).GT.ABS( CDEN ) ) THEN
    *
    *        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.
          END IF
    *
    *     Scale the vector X by MUL
    *
          CALL SSCAL( N, MUL, SX, INCX )
    *
          IF( .NOT.DONE )
         $   GO TO 10
    *
          RETURN
    *
    *     End of SRSCL
    *
          END