[Info-vax] Alpha Fortran data alignment

[Richard B. Gilbert]

glen herrmannsfeldt wrote:
> Richard B. Gilbert <rgilbert88 at comcast.net> wrote:
>> tadamsmar wrote:
>>> I was checking the locations of variables.
>  
>>> If I run this:
>  
>>>         integer*2 prmidx
>>>         real*4 vlu
>>>         prmidx = 1
>>>         vlu = 10000000
>>>         call sub(prmidx,%loc(prmidx),%loc(vlu))
>>>         end
>>>         subroutine sub(prmidx,lp,lv)
>>>         integer*4 prmidx,lv,lp
>>>         type *,prmidx,lp,lv
>>>         end
>  
>>>           1      196608      196616
>  
>>> But if I change prmidx to real*4 in main and real*8 in
>>> the sub, I get:
>  
>>>   128.000036285423           196608      196612
>  
>>> It appear that 8 bytes are allocated for an integer*2 and 4 bytes are
>>> allocated for a real*4
> 
> There is no requirement that variables be allocated in memory
> in the order that they are declared.  Sometimes the compiler even
> needs temporary variables that might also be allocated.
>  
>>> Why is this?
>  
>> Because you are breaking all the rules!!!!!!!
>  
>> You have assigned different sizes (INTEGER*2 and INTEGER*4) for the same 
>> variable in MAIN and SUB.  The subroutine will see 16 bits of data and 
>> 16 bits of garbage.
> 
> That is true, but completely unrelated to the question being asked.
> The question only has to do with the addresses of the variables
> in the main program.  %loc() finds the address and passes that
> as an integer.  The OP only was asking about the sizes and 
> positions in memory of the variables.
> 

I suppose I could simply ignore the errors but code like that pushes 
several of my buttons!  I used to make my living helping the computer 
illiterate write successful programs.

If someone posts Fortran code that is not logically and syntactically 
correct and I see it, I'm likely to comment.  If you are not the author 
of the code in question, please feel free to ignore my comments.