SUBROUTINE CHPR (UPLO, N, ALPHA, X, INCX, AP)
C     .. Scalar Arguments ..
      REAL               ALPHA
      INTEGER            INCX, N
      CHARACTER*1        UPLO
C     .. Array Arguments ..
      COMPLEX            AP( * ), X( * )
C     .. Parameters ..
      COMPLEX            ZERO
      PARAMETER        ( ZERO = ( 0.0E+0, 0.0E+0 ) )
C     .. Local Scalars ..
      COMPLEX            TEMP
      INTEGER            I, INFO, IX, J, JX, K, KK, KX
C     .. External Functions ..
      LOGICAL            LSAME
      EXTERNAL           LSAME
C     .. External Subroutines ..
      EXTERNAL           XERBLA
C     .. Intrinsic Functions ..
      INTRINSIC          CONJG, REAL
C***FIRST EXECUTABLE STATEMENT  CHPR
C
C     Test the input parameters.
C
      INFO = 0
      IF     ( .NOT.LSAME( UPLO, 'U' ).AND.
     $         .NOT.LSAME( UPLO, 'L' )      )THEN
         INFO = 1
      ELSE IF( N.LT.0 )THEN
         INFO = 2
      ELSE IF( INCX.EQ.0 )THEN
         INFO = 5
      END IF
      IF( INFO.NE.0 )THEN
         CALL XERBLA( 'CHPR  ', INFO )
         RETURN
      END IF
C
C     Quick return if possible.
C
      IF( ( N.EQ.0 ).OR.( ALPHA.EQ.REAL( ZERO ) ) )
     $   RETURN
C
C     Set the start point in X if the increment is not unity.
C
      IF( INCX.LE.0 )THEN
         KX = 1 - ( N - 1 )*INCX
      ELSE IF( INCX.NE.1 )THEN
         KX = 1
      END IF
C
C     Start the operations. In this version the elements of the array AP
C     are accessed sequentially with one pass through AP.
C
      KK = 1
      IF( LSAME( UPLO, 'U' ) )THEN
C
C        Form  A  when upper triangle is stored in AP.
C
         IF( INCX.EQ.1 )THEN
            DO 20, J = 1, N
               IF( X( J ).NE.ZERO )THEN
                  TEMP = ALPHA*CONJG( X( J ) )
                  K    = KK
                  DO 10, I = 1, J - 1
                     AP( K ) = AP( K ) + X( I )*TEMP
                     K       = K       + 1
   10             CONTINUE
                  AP( KK + J - 1 ) = REAL( AP( KK + J - 1 ) )
     $                               + REAL( X( J )*TEMP )
               ELSE
                  AP( KK + J - 1 ) = REAL( AP( KK + J - 1 ) )
               END IF
               KK = KK + J
   20       CONTINUE
         ELSE
            JX = KX
            DO 40, J = 1, N
               IF( X( JX ).NE.ZERO )THEN
                  TEMP = ALPHA*CONJG( X( JX ) )
                  IX   = KX
                  DO 30, K = KK, KK + J - 2
                     AP( K ) = AP( K ) + X( IX )*TEMP
                     IX      = IX      + INCX
   30             CONTINUE
                  AP( KK + J - 1 ) = REAL( AP( KK + J - 1 ) )
     $                               + REAL( X( JX )*TEMP )
               ELSE
                  AP( KK + J - 1 ) = REAL( AP( KK + J - 1 ) )
               END IF
               JX = JX + INCX
               KK = KK + J
   40       CONTINUE
         END IF
      ELSE
C
C        Form  A  when lower triangle is stored in AP.
C
         IF( INCX.EQ.1 )THEN
            DO 60, J = 1, N
               IF( X( J ).NE.ZERO )THEN
                  TEMP     = ALPHA*CONJG( X( J ) )
                  AP( KK ) = REAL( AP( KK ) ) + REAL( TEMP*X( J ) )
                  K        = KK               + 1
                  DO 50, I = J + 1, N
                     AP( K ) = AP( K ) + X( I )*TEMP
                     K       = K       + 1
   50             CONTINUE
               ELSE
                  AP( KK ) = REAL( AP( KK ) )
               END IF
               KK = KK + N - J + 1
   60       CONTINUE
         ELSE
            JX = KX
            DO 80, J = 1, N
               IF( X( JX ).NE.ZERO )THEN
                  TEMP    = ALPHA*CONJG( X( JX ) )
                  AP( KK ) = REAL( AP( KK ) ) + REAL( TEMP*X( JX ) )
                  IX      = JX
                  DO 70, K = KK + 1, KK + N - J
                     IX      = IX      + INCX
                     AP( K ) = AP( K ) + X( IX )*TEMP
   70             CONTINUE
               ELSE
                  AP( KK ) = REAL( AP( KK ) )
               END IF
               JX = JX + INCX
               KK = KK + N - J + 1
   80       CONTINUE
         END IF
      END IF
C
      RETURN
C
C     End of CHPR  .
C
      END