Generic_Rational

Generic_Rational

[hnptz]

On http://rosettacode.org/wiki/Arithmetic/Rational/Ada there is an Ada-package which is OK as it is. It says that the package can be instantiated with any integer type. However, I tried to instantiate it with Long_Integer.
I also used Ada.Numerics.Long_Elementary_Functions. 

Now, the Test_Rational programm does not work anymore. The function "/" is perhaps not in compliance with Long_Integer. I wonder if the declarative part in Test_Rational has a false effect.

What are your suggestions to make it working for Long_Integer numbers as well?

best,

montgrimpulo
 

Re: Generic_Rational

[Simon Wright]

hnptz@yahoo.de writes:

> On http://rosettacode.org/wiki/Arithmetic/Rational/Ada there is an
> Ada-package which is OK as it is. It says that the package can be
> instantiated with any integer type. However, I tried to instantiate it
> with Long_Integer.

And the instantiation compiles fine.

> I also used Ada.Numerics.Long_Elementary_Functions. 

There was no need for that.

> Now, the Test_Rational programm does not work anymore. The function
> "/" is perhaps not in compliance with Long_Integer. I wonder if the
> declarative part in Test_Rational has a false effect.
>
> What are your suggestions to make it working for Long_Integer numbers
> as well?

When the test program says

   for Candidate in 2..2**15 loop

Candidate is of type Integer (see ARM 3.6(17..18)[1], so that when it
says

         Sum  : Rational := 1 / Candidate;

there would need to be a function

   function "/" (L, R : Integer) return Rational

but the only "/" that returns Rational and takes integer types takes
Long_Integers.

Recast the loop as

   for Candidate in Long_Integer'(2)..2**15 loop

or

   for Candidate in Long_Integer range 2..2**15 loop

and now there's a similar problem with

         for Divisor in 2..Integer (Sqrt (Float (Candidate))) loop

...

[1] http://www.ada-auth.org/standards/rm12_w_tc1/html/RM-3-6.html#p17

Re: Generic_Rational

[hnptz]

Thanks, it's working now. Nevertheless a further question:

Simon wrote

"... When the test program says 

   for Candidate in 2..2**15 loop 

Candidate is of type Integer (see ARM 3.6(17..18)[1], so that when it 
says ... "

Does a loop from 2..2**15 exceed the bounds of an integer type by one ? (see also 3.5.4(21)). If so, then Candidate should be become a Long_Integer type following 3.6(19). What may be wrong with this interpretation?

Re: Generic_Rational

[Simon Wright]

hnptz@yahoo.de writes:

> Thanks, it's working now. Nevertheless a further question:
>
> Simon wrote
>
> "... When the test program says 
>
>    for Candidate in 2..2**15 loop 
>
> Candidate is of type Integer (see ARM 3.6(17..18)[1], so that when it 
> says ... "
>
> Does a loop from 2..2**15 exceed the bounds of an integer type by one
> ? (see also 3.5.4(21)). If so, then Candidate should be become a
> Long_Integer type following 3.6(19). What may be wrong with this
> interpretation?

(18) says "If the type of the range resolves to root_integer, then the
discrete_subtype_definition defines a subtype of the predefined type
Integer with bounds given by a conversion to Integer of the bounds of
the range"; and I'm pretty sure that means "the largest integer type
suported by the implementation".

GNAT's Integer is -2**31 .. 2**31 -1 , so 2**15 is well
within. Long_Integer is -2**63 .. 2**63 - 1.

   for Candidate in 2..2**31 loop
        >>> value not in range of type "Standard.Integer"
        >>> static expression fails Constraint_Check

   for Candidate in 2..2**63 loop
        >>> warning: non-static universal integer value out of range
        >>> warning: "Constraint_Error" will be raised at run time
        >>> value not in range of type "Standard.Integer"
        >>> static expression fails Constraint_Check

Re: Generic_Rational

[Jeffrey R. Carter]

On 02/17/2018 03:13 PM, hnptz@yahoo.de wrote:
> 
> Does a loop from 2..2**15 exceed the bounds of an integer type by one ? (see also 3.5.4(21)). If so, then Candidate should be become a Long_Integer type following 3.6(19). What may be wrong with this interpretation?

That's the minimum range required of the predefined type Integer. The actual 
range is implementation-defined and may be larger. I think the language would be 
better if it defined

type Integer is range -(2 ** 15) + 1 .. 2 ** 15 - 1;

and didn't have the optional Short_ and Long_ types.

-- 
Jeff Carter
"Pray that there's intelligent life somewhere up in
space, 'cause there's bugger all down here on earth."
Monty Python's Meaning of Life
61