Fortran - problem with double precision

I have a small program that read some data from binary file and stores it into normal (unformatted) 开发者_C百科files. Here is the source:

  Program calki2e
  IMPLICIT NONE
!
       DOUBLE PRECISION VAL
      INTEGER P,Q,R,S
    INTEGER  IREC2C
      PARAMETER( IREC2C=15000)
      INTEGER  AND,RSHIFT,LABEL,IMBABS,NX,IB,NFT77
      INTEGER  IND
      DIMENSION IND(IREC2C)
    DOUBLE PRECISION  XP
      DIMENSION XP(IREC2C)
      CHARACTER(LEN=12) :: FN77 = 'input08'
    CONTINUE
    NFT77=77
!----------------------------------------------------------------------
2   CONTINUE
c
    open(unit=NFT77,file=FN77,STATUS='OLD',
     +ACCESS='SEQUENTIAL',FORM='UNFORMATTED')
    open(unit=13,file='calki2e.txt')
    REWIND(77)
4100    continue
     READ(77) NX,IND,XP
       IMBABS=IABS(NX)
       DO 100 IB=1,IMBABS
            LABEL=IND(IB)
            P= AND(RSHIFT(LABEL, 24),255)
            Q= AND(RSHIFT(LABEL, 16),255)
            R= AND(RSHIFT(LABEL,  8),255)
            S= AND(       LABEL     ,255)
            VAL=XP(ib)  
            IF(P.EQ. Q) VAL=VAL+VAL                               
            IF(R .EQ. S)  VAL=VAL+VAL                                    
            IF((P .EQ. R).AND.(Q .EQ. S)) VAL=VAL+VAL 
    write(13,*)P,Q,R,S,val
100 CONTINUE
    IF (NX.GT.0) GOTO 4100
CRB
      CLOSE(UNIT=NFT77)
!
    END

When I compile it using gfortran I obtain double precision in output file but with g77 I get only single precision. What it wrong and how to change it?

Do you mean the "write (13, *) statement. This is "list directed" output. It is a convenience I/O with few rules -- what you get will depend upon the compiler -- it is best used for debugging and "quick and dirty" programs. To reliably get all the digits of double precision, change to a formatted output statement, specifying the number of digits that you need. (It is probably best to switch to gfortran anyway, as g77 is no longer under development.)

your numbers are double precision but you are printing them in free format. You have to specify an explicit format

If you want to keep your code F77, try something like

      write(13,1000) P,Q,R,S,val
1000  format(1X,4I7,1X,1E14.10)

The "1X"s mean one space, "4I7" means four seven-width integers, and 1E14.10 means one fourteen-charater width scientific-notation real number with 10 significant digits. Feel free to mess around with the numbers to get it to look right.

This is a pretty good tutorial on the topic.

I would be tempted to set the format on your write statement to something explicit, rather than use * in write(13,*)P,Q,R,S,val.