!$Author$
!$Date$
!$Revision$
!$HeadURL$

      SUBROUTINE RANDM(X, A, MRND, RNUMB)
      
      use wepp_interface_defs, ignore_me=>RANDM
      
      implicit none
!
!     + + + PURPOSE + + +
!
!     RANDM COMPUTES RANDOM NUMBERS BY A MULTIPLICATIVE CONGRUENTIAL
!     METHOD:
!
!     X = A*X MOD M,  RNUMB=X/M
!
!     NOTE: BGNRND SHOULD BE USED TO INITIALIZE X (THE CHECKS MADE 
!     THERE [A*M AND A CAN BE REPRESENTED EXACTLY IN X AND U] ENSURE 
!     THAT SUCESSIVE VALUES OF X CAN BE CALCULATED EXACTLY)
!
!     THE NUMBER OF SIGNIFICANT DIGITS IN THE RESULT IS ROUGHLY THE 
!     MINIMUM OF:
!     1) THE NUMBER OF SIGNIFICANT DIGITS IN RND, AND
!     2) THE NUMBER OF SIGNIFICANT DIGITS IN U LESS THE NUMBER OF
!        DIGITS OF THE MULTIPLIER IN A
!
!     WHEN U IS DOUBLE PRECISION, ALL THE DIGITS IN RND ARE
!     SIGNIFICANT
!
!     INITIALIZES PARAMETER VALUES FOR HYDROLOGY COMPONENT.
!
!     CALLED FROM PSIINV
!     AUTHOR(S): D. FLANAGAN, J. ASCOUGH
!     VERSION: THIS MODULE TAKEN FROM ASCOUGH STANDALONE IRS CODE
!     DATE CODED:  3-24-2005
!     CODED BY: D. FLANAGAN
!
!
!     + + + ARGUMENT DECLARATIONS + + +

      real, intent(in) :: MRND, A
      real, intent(out) :: RNUMB
      real, intent(inout) :: X
     
!     + + + ARGUMENT DEFINITIONS + + +
!
!     X       -
!     A       -
!     MRND    -
!     RNUMB   - RANDOM NUMBER RETURNED FROM SUBROUTINE
!     
!     + + + LOCAL DECLARATIONS + + +
      REAL V
      DOUBLE PRECISION U

!     + + + LOCAL DEFINITIONS + + +
!     V       - HOLDS INTERMEDIATE RESULTS
!     U       - HOLDS INTERMEDIATE RESULTS

!     + + + END SPECIFICATIONS + + +

      X = A * X
      U = X / MRND
      V = U
      V = AINT(V)
      X = X - V * MRND
!
      IF (X.LT.0.D0) THEN
         V = V - 1.
         X = X + MRND
      END IF
!
      RNUMB = U - V
!
      RETURN
      END