f771 assertion failure

[Toon Moene]

Richard Henderson:

>> >but don't know enough about Fortran to know what the implications
>> >are.  What actually happens?  The subroutine gets fed bad data? 
>> >Something similar to c++'s non-const-reference, which gets fed
>> >the address of a temporary?

Craig:

>> Have you tried "info -f g77 M GLOBALS"?  It *should* answer these
>> questions -- let us know if it doesn't.

Richard:

>  It tells me to use -fno-globals, which is a cookbook
>  answer to get rid of the warning, but does not help me
>  understand the consequences of ignoring the warning --
>  what happens to the bits? Does some data conversion take
>  place?  Since Fortran passes by reference (always?),
>  where does the (new?) data get put, on the stack?  Or
>  does the called function see the bits of the FP number
>  as an integer?

The latter.  It might not be harmful, iff the routine does nothing  
else but using it as internal work space (i.e. it doesn't _read_  
anything stored in the array before initialising it itself).

In the old days, library routines (like this one - from the name  
only I'd guess it computes a Fast Fourier Transform) often requested  
some work space from their callers, because Fortran 77 doesn't  
allow the routine itself to allocate a temporary array whose extent  
is a function of the problem size as passed by the caller.  Nowadays  
we have (Fortran 90) automatic arrays, which solve this problem [  
BTW, g77 also supports these ]

I do agree with Richard that the explanation info -f g77 M GLOBALS  
gives might be hard to understand for non-Fortraners.

HTH,
Toon.