ADAS Subroutine r8fctn

      FUNCTION R8FCTN( STR , IABT )
C-----------------------------------------------------------------------
C
C  **************** FORTRAN77 REAL*8 FUNCTION: R8FCTN ******************
C
C  PURPOSE : TO CONVERT A FLOATING POINT NUMBER STORED IN A STRING
C            INTO A REAL*8 VARIABLE.
C
C  CALLING PROGRAM: GENERAL USE
C
C  FUNCTION:
C
C          (R*8)   R8FCTN  = FUNCTION NAME
C          (C*(*)) STR     = STRING CONTAINING SINGLE FLOATING POINT NO.
C          (I*4)   IABT    = RETURN CODE:
C                               0 => NO ERROR
C                               2 => ERROR (A VALUE 'R8FCTN=0.0' WILL BE
C                                           RETURNED).
C                               9 => OVERFLOW ERROR (EXPONENT  > IUOFLW)
C                                    (A VALUE 'R8FCTN=0.0' RETURNED)
C                              10 => UNDERFLOW ERROR (EXPONENT <-IUOFLW)
C                                    (A VALUE 'R8FCTN=0.0' RETURNED)
C
C          (I*4)   IUOFLW   = PARAMETER = MODULUS OF MAXIMUM ALLOWED
C                                         EXPONENT = 60
C
C          (C*1)   CH0      = PARAMETER = '0'
C          (C*1)   CH9      = PARAMETER = '9'
C          (C*1)   BLANK    = PARAMETER = ' '
C          (C*1)   CPLUS    = PARAMETER = '+'
C          (C*1)   CMINUS   = PARAMETER = '-'
C          (C*1)   CPNT     = PARAMETER = '.'
C          (C*1)   CHE      = PARAMETER = 'E'
C          (C*1)   CHD      = PARAMETER = 'D'
C          (C*1)   CLE      = PARAMETER = 'e'
C          (C*1)   CLD      = PARAMETER = 'd'
C
C          (I*4)   ILEN     = LENGTH OF 'STR' STRING IN BYTES
C          (I*4)   M1       = STARTING BYTE IN 'STR' OF NUMBER
C                             INCLUDING SIGN
C          (I*4)   M2       = LAST BYTE IN 'STR' OF NUMBER
C          (I*4)   IE       = STARTING BYTE OF EXPONENT IN  'STR'
C                             IGNORING ANY SIGN PRESENT.
C          (I*4)   MS       = 0 => MANTISSA HAS NO SIGN
C                             1 => MANTISSA HAS A SIGN
C          (I*4)   IS       = 0 => EXPONENT HAS NO SIGN
C                             1 => EXPONENT HAS A SIGN
C          (I*4)   IPOW     = EXPONENT
C          (I*4)   ICH0     = ICHAR('0')
C          (I*4)   ICH9     = ICHAR('9')
C          (I*4)   ISTR     = ICHAR(CURRENT BYTE POSITION IN 'STR')
C          (I*4)   I        = GENERAL USE
C
C          (L*4)   LMANT    = .TRUE.  => MANTISSA BEING ANALYSED
C                             .FALSE. => EXPONENT BEING ANALYSED
C          (L*4)   LPOINT   = .TRUE.  => DECIMAL POINT FOUND IN MANTISSA
C                             .FALSE. => NO DECIMAL POINT FOUND IN MANT.
C          (L*4)   LFOUND   = .TRUE.  => ALL OF THE INPUT NUMBER BYTES
C                                        HAVE BEEN ASSESSED.
C                             .FALSE. => INPUT NUMBER BYTES STILL BEING
C                                        ASSESSED.
C
C NOTE:     AN ERROR WILL OCCUR (IABT=2) IF THERE IS MORE THAN ONE
C           NUMBER OCCURING IN THE STRING 'STR()'
C
C
C AUTHOR:   PAUL E. BRIDEN (TESSELLA SUPPORT SERVICES PLC)
C           K1/0/81
C           JET EXT. 4569
C
C DATE:     26/10/90
C
C VERSION  : 1.2                          
C DATE     : 20-12-2001
C MODIFIED : Martin O'Mullane
C               - Removed mainframe listing information beyond column 72.
C
C VERSION  : 1.3                          
C DATE     : 03-12-2003
C MODIFIED : Hugh Summers
C               - Allowed lower case 'e' or 'd' in the real number spec.
C
C VERSION  : 1.4
C DATE     : 10-04-2007
C MODIFIED : Allan Whiteford
C               - Modified documentation as part of automated
C		  subroutine documentation preparation.
C
C-----------------------------------------------------------------------
C
C-----------------------------------------------------------------------
      CHARACTER*(*)       STR
      INTEGER             IABT