20000218: AW_APLT

I found some redbook graphics on NOAAport which cause 
AW_APLT to enter in an infinite loop. Some text blocks
appear to be Null padded 2 bytes less than the itotln.
Don't know if this is an intended checksum.

The wave period charts on NOAAport today exhibit this:
WMO Headers: PKQD01 KWNM 181200, PKQD03 KWNM 181200
(NMCGPH0P1, NMCGPH0P3). I can send you these products if needed. 

The problem appears in the main loop, where the IF block
decrements ibeg
DO WHILE ( ibeg .le. itotln )
...
C
C*            Storing text in string.
C
              ELSE  IF ( .not. textfl ) THEN
                IF ( ispch .ne. 0 ) THEN
                DO WHILE ( ( ( ispch .ge. 32) .and.
     +              ( ispch .le. 127 ) ) .and. ( ibeg .le. itotln ) )
                    stchar ( i:i ) = char ( b ( ibeg ) )
                    i = i + 1
                    ibeg = ibeg + 1
                    ispch = ibits( ibte (ibeg), 0, 8)
                    textfl = .true.
                END DO
                ibeg = ibeg - 1

...
           ibeg = ibeg + 1
C
C*         Check for I = 0 (Chiz)
C
           if(i.eq.0) then
              iret = -1
              return
           endif
C
        END DO

When ispch is 0, ibeg is not incremented.
I added a check just before the end_do to prevent the infinite loop
by returning to the calling routine- though you might want to
stay in the routine and finish the checksum.

I also added a check in the debug printing to avoid trying to write the
stchar(1:i) when i < 1:
                    write(14,*)'CHARACTER STRING:'
                    if(i .gt. 0) then
                       write(14,68) stchar(1:i)
                    else
                       write(14,*) 'No char ',i
                    endif


Steve Chiswell
Unidata User Support