Fortran 77 read unformatted sequence data from old sun machine

Question 1

Out of this scope, for some reason a deep method in charge of reading the file is called in the 1100 loop. That was causing to read the file more times than necessary. Find below the fixed code:

* 1100 CONTINUE 
     CALL   GDREDX         !! read data
 O         ( GDATA , IEOD  ,
 O           HITEMD, HTITL , HUNIT , HDSET , 
 O           TIME  , TDUR  , KLEVS ,
 I           IFILE , HITEM , HDFMT ,
 I           IMAXD , JMAXD , 
 I           IDIMD , JDIMD , KDIMD           )
     IF ( IEOD .EQ. 0  ) THEN
         WRITE (6,*) ' IRWGD.F::GDRDTS: TSEL0=', TSEL0
         WRITE (6,*) ' IRWGD.F::GDRDTS: TSEL1=', TSEL1
         WRITE (6,*) ' IRWGD.F::GDRDTS: TIME=', TIME
*            IF (    ((TSEL0.GE.0).AND.(TIME.LT.TSEL0)) 
*     &          .OR.((TSEL1.GE.0).AND.(TIME.GT.TSEL1)) ) THEN
*                     GOTO 1100
*            ENDIF
        ENDIF
*
  RETURN
  END

That mislead me in order to figure out what was going on.

Question 2

Here is whats going on - first this This is definitely a Big Enfian file. The first 4 bytes

00000400

are the big end 4 byte integer 1024, which is the length of your first record. which agrees with the length of HEAD (per comment) Now note that 00000400 is repeated at byte position 1024+4 exactly (hex dump line 400) as you should expect for a fortran unformatted file...so far so good.

Now the next 4 bytes

0002 8000

begin the second record. (edit correcting mistake) This is 163840 (2*16^4+8*16^3) You should find that repeated at position 1024+8+163840+4 in the hex dump. (should be line 028400 i think..)

Here is the problem: in your code you are reading that 160 kilobyte record into a single 4 byte variable, then moving on to the next record. My guess you are seeing that alternating 10^-19 because every other record is of type character.

In unformatted fortran you must read a whole record in one shot - try reading the entire array (without the loop..)

READ ( IFILE )SDATA

assuming sdata is dimensioned to hold 160 kb of course. (eg. real*4 (40960) )

Question 3

The answer to your problem is in the edit that I missed. Thanks also to george's arithmetic---which I hadn't bothered to do.

We can safely say that the record headers are correct, and that you can solve your problem with the endian conversion.

So, the problem is: reads with an implied-do loop are not equivalent to reads inside a do loop.

That is: read(unit) (i(j), j=1,5) is not the same as

do j=1,5
  read(unit) i(j)
end do

In the first, reading of the five values is from one record, in the second each is read from a distinct record.

You should, then, revert your change. If you want to do the same diagnostics, however, you can do something like

READ ( IFILE, IOSTAT=IEOD) (SDATA(IJK), IJK=1, IJKNUM )
WRITE (6, '("IGTIO::GTZZRD: iteration='", I0.0, F12.8)') (IJK, SDATA(IJK), IJK=1,IJKNUM)