! $Id: lmdz_ran1.f90 5117 2024-07-24 14:23:34Z fairhead $

MODULE lmdz_ran1
  IMPLICIT NONE; PRIVATE
  PUBLIC ran1
CONTAINS

  FUNCTION RAN1(IDUM)
    IMPLICIT NONE
    REAL :: RAN1
    REAL, SAVE :: R(97)
    REAL, PARAMETER :: RM1 = 3.8580247E-6, RM2 = 7.4373773E-6
    INTEGER, SAVE :: IFF = 0
    INTEGER, save :: ix1, ix2, ix3
    INTEGER, PARAMETER :: M1 = 259200, IA1 = 7141, IC1 = 54773
    INTEGER, PARAMETER :: M2 = 134456, IA2 = 8121, IC2 = 28411
    INTEGER, PARAMETER :: M3 = 243000, IA3 = 4561, IC3 = 51349
    INTEGER :: IDUM, J

    IF (IDUM<0.OR.IFF==0) THEN
      IFF = 1
      IX1 = MOD(IC1 - IDUM, M1)
      IX1 = MOD(IA1 * IX1 + IC1, M1)
      IX2 = MOD(IX1, M2)
      IX1 = MOD(IA1 * IX1 + IC1, M1)
      IX3 = MOD(IX1, M3)
      DO J = 1, 97
        IX1 = MOD(IA1 * IX1 + IC1, M1)
        IX2 = MOD(IA2 * IX2 + IC2, M2)
        R(J) = (REAL(IX1) + REAL(IX2) * RM2) * RM1
      END DO
      IDUM = 1
    ENDIF
    IX1 = MOD(IA1 * IX1 + IC1, M1)
    IX2 = MOD(IA2 * IX2 + IC2, M2)
    IX3 = MOD(IA3 * IX3 + IC3, M3)
    J = 1 + (97 * IX3) / M3
    IF(J>97.OR.J<1) stop 1
    RAN1 = R(J)
    R(J) = (REAL(IX1) + REAL(IX2) * RM2) * RM1

  END FUNCTION RAN1
END MODULE lmdz_ran1