Re: How do you bitwise operations in Ada '83 and '95

[Marius Amado-Alves <marius@amado-alves.info>]

>> Implemented as a modular type the predefined relation
>> functions are gratis--and surely correct.
>
> Only if you've carefully laid out the order of the bits so that  
> will work.

Sure, but that's really easy, no? Year, Month, Day, Seconds...

> Which is much more likely to ruin the alignment of the bit-field  
> components
> (an important part of maximum performance).

For records. For a 64-bit unit it does not matter for the "<"  
functions where the fields are.

>> And the expressions are not
>> complex. Once you get the masks and magnitudes right, it's simply
>>
>> Part := (Whole and Mask) / Magnitude.
>
> But that's for each component. Surely you do other operations (like
> difference in seconds) where the expressions are  far more complex?

Actually, in this case, no. I leave it to Ada.Calendar. Convert,  
compute, convert. This limitation is documented.

> All-in-all, I prefer the record representation.

For Calendar_64 I specifically wanted a 64-bit string, it was a  
requirement.

If I was to implement Ada.Calendar I think I would use a record too,  
because it is a private type by definition, so I would have to write  
the "<" functions anyway.

> Janus/Ada Calendar.Time implementation is a 64-bit record type

Just curious: is it aligned properly i.e. if you uncheckedly convert  
to a 64-bit modular will the modular "<" functions work properly i.e.  
represent the relations between the dates properly?

Of course a Calendar_64 for a specific compiler/platform could take  
advantage of the respective Ada.Calendar representation.