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From: tom@itc.univie.ac.at (Tom Kovar)
Newsgroups: comp.lang.fortran
Subject: Re: Cheating on the types
Message-ID: <1991Mar28.220027.10553@nestroy.wu-wien.ac.at>
Date: 28 Mar 91 22:00:27 GMT
References: <1991Mar20.195732.15376@appmag.com> <4554@alliant.Alliant.COM> <1991Mar25.163447.10166@cl.cam.ac.uk>
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Organization: Inst. of Theoretical Chemistry, University of Vienna
Lines: 38

In article <1991Mar20.195732.15376@appmag.com> pa@appmag.com (Pierre Asselin) writes:
}This simplified fragment violates the standard by passing reals to a
}routine that expects integers.
}
}      program wrong
}      real rin, rout
}      rin= 0.577215665          ! or whatever...
}      call icopy(rin, rout)
}      write(6,*) rout
}      end
}
}      subroutine icopy(iin, iout)
}      integer iin, iout
}      iout= iin
}      return
}      end
}
}Seems fairly innocuous, though.  Q:  are there implementations
}where it would fail ?
>
>From the mists of time: on TITAN (and other Atlas-1 and Atlas-2 Fortran
>implementations as well, I expect) integers were halfwords (24 bits) while
>reals were words (48 bits). The above code would not have worked. 
>
>This implementation long preceded the Fortran 77 rules on storage units. 
>However, in some cases it was compatible with them: for example, an INTEGER
>array and a REAL array with the same number of elements that were 
>EQUIVALENCEd or overlaid in COMMON would correspond 1:1 (half the space  
>in the INTEGER array was "wasted"). Copying the INTEGER array element by
>element to another such INTEGER/REAL pair would not have the effect of   
>copying the REAL array (only half the bits would be moved), and there is 
>nothing in the Fortran 77 standard to say that it should.

Another wonderfull thing - on old Telefunken TR440 (or something like that)
using a 48 bit word, I think 2 bits were passed within the word, 
identifying the kind of the argument... So you would have been caught... :-)

						Tom Kovar