ADAS Subroutine b2nfas

       SUBROUTINE B2NFAS(X,XA,N,YA,Y,DY,C1,C2,C3,C4,FORM,IFORMS)        
C
       IMPLICIT REAL*8(A-H,O-Z)                                         
C-----------------------------------------------------------------------
C
C  ****************** FORTRAN77 SUBROUTINE: B2NFAS *********************
C
C PURPOSE:
C  SUBROUTINE TO PROVIDE A SPLINE INTERPOLATE MAKING USE OF SPECIFIED
C  ASYMPTOTIC BEHAVIOUR
C
C
C  USES LABELLED COMMON /SPL3/
C
C  INPUT
C      X=REQUIRED X-VALUE
C      X(I)=KNOTS
C      N=NUMBER OF KNOTS
C      C1(I,J)=1ST SPINE COEFFICIENT PRECURSOR
C      C2(I,J)=2ND SPINE COEFFICIENT PRECURSOR
C      C3(I,J)=3RD SPINE COEFFICIENT PRECURSOR
C      C4(I,J)=4TH SPINE COEFFICIENT PRECURSOR
C      FORM=EXTERNAL FUNCTION SPECIFYING ASYMPTOTIC FORMS
C      IFORMS=INDEX OF REQUIRED FORM
C  OUTPUT
C      Y=RETURNED Y-VALUE
C      DY=RETURNED DERIVATIVE
C
C NOTES: THIS ROUTINE IS NOT YET PROPERLY ANNOTATED
C
C UNIX-IDL PORT:
C
C VERSION: 1.1                          DATE: 06-03-96
C MODIFIED: TIM HAMMOND (TESSELLA SUPPORT SERVICES PLC)
C               - PUT UNDER S.C.C.S. CONTROL
C
C-----------------------------------------------------------------------
C
      INTEGER             IFORMS,      N
      REAL*8              C1(10,9),    C2(10,9),    C3(10,9)
      REAL*8              C4(10,9),    DY,          X,           XA(10)
      REAL*8              Y,           YA(10)