Re: Why no 'Floor for fixed point types

[Nick Roberts <nick.roberts@acm.org>]

Randy Brukardt wrote:

>>Do you think fixed point types should have a Floor attribute?
> 
> The original answer to this showed that for some fixed point types, it
> wouldn't be possible to implement it accurately. Thus, it is much better to
> show what you are doing via a conversion to an appropriate float type.
> Hopefully the compiler can note the easy cases and eliminate the float
> operations.

To my mind, I would not expect this form of optimisation in any compiler.

Would it not be reasonable to provide 'Floor for fixed-point types which 
fulfil certain conditions?

For example, it might be required that the delta be less than 1.0 (and that 
the range includes at least one integer). Alternatively, it might be 
required that the delta is precisely 1.0 (with conditions on the range).

These conditions might be imposed statically (erroneous) or dynamically 
(raising an exception). I suppose the dynamic option would fit easier with 
the possibility of the fixed point type being a generic formal.

After all, if Float'Floor(Float(X)) is going to produce a silly result 
(without itself raising Constraint_Error), what's wrong with 
Some_Fixed'Floor(X) raising Constraint_Error? Surely that would actually be 
better?

-- 
Nick Roberts