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From: bgoldma@geinah.UUCP
Newsgroups: comp.bugs.4bsd
Subject: bug in f77 on 4.3 bsd
Message-ID: <928@charon.unm.edu>
Date: Thu, 23-Apr-87 18:19:03 EST
Article-I.D.: charon.928
Posted: Thu Apr 23 18:19:03 1987
Date-Received: Sat, 25-Apr-87 08:35:22 EST
Sender: news@charon.unm.edu
Lines: 37

I have found a bug in f77 released with 4.3.  When a comparison of a
substring delimited by nonevaluated expressions is anded with another
the results are not always correct.  Here is a sample program illustrating
this.  The problem is because "(1)" is evaluated differently than "1".
By the same token, using a variable such as "j" will work, but using
"j+1" will not.  It has something to do with when it is evaluated and
compiling with the optimizer usually fixes this by cheating.  I do not
have a fix for this and I do not know exactly what the error is.



      program bug
      character*2 atom
      logical row
      atom(1:1) = 'H'
      atom(2:2) = 'H'
      if(atom((1):(1)).eq.'H') print*,'first true'
      if (atom((2):(2)).eq.'H') print*,'second true'

C HERE IS THE BUG
      row = ((atom((1):(1)).eq.'H').and.(atom((2):(2)).eq.'H'))
	print*,'first and second is ',row
C The problem the f77 has is evaluating an integer expression used
C as substring delimiters when in a boolean and the boolean is
C only temporary.  This is not the case if the integer is a constant
C as can be seen by the example below.
C HERE IS THE BUG

C HERE IS THE CORRECT OUTPUT
      row = ((atom(1:1).eq.'H').and.(atom(2:2).eq.'H'))
	print*,'first and second is ',row
C HERE IS THE CORRECT OUTPUT
      end



				BILL Goldman