Re: How unchecked conversion works?

[Stephen Leake <stephen_leake@acm.org>]

None <none@none.it> writes:

> well, I try to explain. I have those types for example
> 
> type fixed is delta 0.03 range -90.0..90.0
> for fixed'size use 16
> 
> and
> 
> type inte is range -32768..32767
> for inte'size use 16
> 
> 
> and a new function that renames unchecked_conversion to come from
> fixed to inte (probably an inefficient way, but I have to do this
> way), so I'd like to predict on paper which value of inte type
> corresponds to 89.09 for example: what kind of calculus should I do?
> This depends on something else? Thanks again!

If you are trying to control the exact representation of the fixed
point type, you need to specify the 'Small for the type:

for fixed'small use 0.03;

Then the least significant bit of 'fixed' represents a value of 0.03;
89.09 / 0.03 is 2970, so that is the result of the unchecked
conversion you are discussing.

This is explained in sections 3.5.9 and 3.5.10 of the Ada Reference
Manual, but it is somewhat obscure.

-- 
-- Stephe