4 ms·

Aliasing can be a problem in Fortran too. Decades ago I was a Fortran developer and encountered a very odd bug in which the wrong values were being calculated.

by bregma 10mo ago

Aliasing can be a problem in Fortran too. Decades ago I was a Fortran developer and encountered a very odd bug in which the wrong values were being calculated. After a lot of investigation I tracked it down to a subroutine call in which a hard-coded zero was being passed as an argument. It turned out that in the body of that subroutine the value 4 was being assigned to that parameter for some reason. The side effect was that the value of zero because 4 for the rest of the program execution because Fortran aliases all parameters since it passes by descriptor (or at least DEC FORTRAN IV did so on RSX/11). As you can imagine, hilarity ensued.

pklausler 10mo ago
How does this bug concern aliasing?
- Etheryte 10mo ago
  It's literally in the description? Because of aliasing, a variable that should've been zero became four.
  - pklausler 10mo ago
    It wasn't a variable.
    - Etheryte 10mo ago
      It wasn't intended to be a variable, but it did become one. Its value varied, it's in the name.
      - pklausler 10mo ago
        But this is just Fortran's call-by-reference in action. It's not aliasing.
- mrspuratic 10mo ago
  In old school FORTRAN (I only recall WATFOR/F77, my uni's computers were quite ancient) subroutine (aka "subprogram") parameters are call-by-reference. If you passed a literal constant it would be treated as a variable in order to be aliased/passed by reference. Due to "constant pooling", modifications to a variable that aliased a constant could then propagate throughout the rest of the program where that constant[sic] was used. "Passing constants to a subprogram" https://www.ibiblio.org/pub/languages/fortran/ch1-8.html https://www.ibiblio.org/pub/languages/fortran/ch1-8.html