CODEWITHSUNDEEP
fortran
Michał
Michał

Reputation: 11

Fortran - problem with double precision

I have a small program that read some data from binary file and stores it into normal (unformatted) 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?

Upvotes: 1

Views: 3930

Answers (4)

High Performance Mark
High Performance Mark

Reputation: 78364

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.

Upvotes: 0

Dan
Dan

Reputation: 12705

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.

Upvotes: 0

M. S. B.
M. S. B.

Reputation: 29401

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.)

Upvotes: 1

Stefano Borini
Stefano Borini

Reputation: 143925

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

Upvotes: 0

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