Modify value - type duration

Modify value - type duration

[Andreas.Schmidl]

Hello!

I started programming in Ada for about a month. Because of that my
knowledge isn't really good, but will be better every day ;-)
I have a problem to modify a fixed point value  (type duration).

I want to cut all before the point. Example:
---------------------------------------------------
var1 : duration := 12.345;
var2 : duration;

var2 := cutIt(num => var1);
---------------------------------------------------

var2 is now 0.345. To implement the function "cutIt" I tested an idea.
I converte var1 to an integer:

---------------------------------------------------
function cutIt(var : duration) return duration is

tempvar : integer;

begin
	tempvar := integer(var);
	return (var - duration(tempvar));

end cutIt;
--------------------------------------------------

But this isn't a solution. Converting to integer with integer(...)
round the value.
Example:
12.345 ---> 12
12.854 ---> 13

Is there any other more elegant and functional solution in Ada?

Thanks for your help!

Best regards!

Andreas

Re: Modify value - type duration

[Jeffrey R. Carter]

Andreas.Schmidl@googlemail.com wrote:
> function cutIt(var : duration) return duration is
> 
> tempvar : integer;
> 
> begin
> 	tempvar := integer(var);
> 	return (var - duration(tempvar));
> 
> end cutIt;
> 
> But this isn't a solution. Converting to integer with integer(...)
> round the value.
> Example:
> 12.345 ---> 12
> 12.854 ---> 13
> 
> Is there any other more elegant and functional solution in Ada?

Back in the good old days of Ada 83, we'd subtract 0.5 from the value before 
converting to an integer type.

Note that a Duration may contain a value that cannot be converted to Integer.

These days, you can use an appropriate floating-point type and the 'Truncation 
attribute function to get the integer part:

function Cut_It (Value : in Duration) return Duration is
    type Big is digits System.Max_Digits;
begin -- Cut_It
    return Value - Duration (Big'Truncation (Big (Value) ) );
end Cut_It;

-- 
Jeff Carter
"You a big nose have it."
Never Give a Sucker an Even Break
107

Re: Modify value - type duration

[Adam Beneschan]

On Nov 5, 2:47 pm, "Jeffrey R. Carter"
<spam.jrcarter....@spam.acm.org> wrote:
> Andreas.Schm...@googlemail.com wrote:
> > function cutIt(var : duration) return duration is
>
> > tempvar : integer;
>
> > begin
> >    tempvar := integer(var);
> >    return (var - duration(tempvar));
>
> > end cutIt;
>
> > But this isn't a solution. Converting to integer with integer(...)
> > round the value.
> > Example:
> > 12.345 ---> 12
> > 12.854 ---> 13
>
> > Is there any other more elegant and functional solution in Ada?
>
> Back in the good old days of Ada 83, we'd subtract 0.5 from the value before
> converting to an integer type.
>
> Note that a Duration may contain a value that cannot be converted to Integer.
>
> These days, you can use an appropriate floating-point type and the 'Truncation
> attribute function to get the integer part:
>
> function Cut_It (Value : in Duration) return Duration is
>     type Big is digits System.Max_Digits;
> begin -- Cut_It
>     return Value - Duration (Big'Truncation (Big (Value) ) );
> end Cut_It;

Hmmm ... now I wonder why there isn't a Truncation attribute for fixed-
point types?  Maybe nobody before Andreas ever thought they'd need
one.  Might be useful.  (Also Floor, Ceiling.)

A possible problem with the floating-point conversion solution is that
there may be cases where you lose accuracy---if, e.g., the largest
floating-point type and fixed-point systems supported on the machine
are both 64 bits.  Since a floating-point number needs room for an
exponent, it's possible to define a fixed-point type with more bits in
the integer part than can be represented in the mantissa of a floating-
point type, e.g.

   type Pathological is delta 0.25 range -(2.0**61) .. (2.0**61-0.25);

although I don't think that would be a problem with the Duration type.

                             -- Adam

Re: Modify value - type duration

[Jeffrey R. Carter]

Adam Beneschan wrote:
> 
> Hmmm ... now I wonder why there isn't a Truncation attribute for fixed-
> point types?  Maybe nobody before Andreas ever thought they'd need
> one.  Might be useful.  (Also Floor, Ceiling.)

No, I wondered about that long ago.

> A possible problem with the floating-point conversion solution is that
> there may be cases where you lose accuracy---if, e.g., the largest
> floating-point type and fixed-point systems supported on the machine
> are both 64 bits.  Since a floating-point number needs room for an
> exponent, it's possible to define a fixed-point type with more bits in
> the integer part than can be represented in the mantissa of a floating-
> point type, e.g.

One must always be careful in such cases that the conversion will not fail or 
lose important bits.

-- 
Jeff Carter
"You a big nose have it."
Never Give a Sucker an Even Break
107

Re: Modify value - type duration

[Keith Thompson]

"Jeffrey R. Carter" <spam.jrcarter.not@spam.acm.org> writes:
> Adam Beneschan wrote:
>> Hmmm ... now I wonder why there isn't a Truncation attribute for
>> fixed-
>> point types?  Maybe nobody before Andreas ever thought they'd need
>> one.  Might be useful.  (Also Floor, Ceiling.)
>
> No, I wondered about that long ago.
>
>> A possible problem with the floating-point conversion solution is that
>> there may be cases where you lose accuracy---if, e.g., the largest
>> floating-point type and fixed-point systems supported on the machine
>> are both 64 bits.  Since a floating-point number needs room for an
>> exponent, it's possible to define a fixed-point type with more bits in
>> the integer part than can be represented in the mantissa of a floating-
>> point type, e.g.
>
> One must always be careful in such cases that the conversion will not
> fail or lose important bits.

Well, you *could* do an Unchecked_Conversion to an appropriate integer
type, use integer arithmetic to truncate, and then convert back to
Duration.  It's ugly, but it should work on most systems, and it
avoids any accuracy problems.

Doing this in a way that will work under one specific compiler is
fairly straightforward.  Doing it reasonably portably is harder.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

Re: Modify value - type duration

[Randy Brukardt]

"Jeffrey R. Carter" <spam.jrcarter.not@spam.acm.org> wrote in message 
news:nasQk.422242$yE1.14213@attbi_s21...
> Adam Beneschan wrote:
>>
>> Hmmm ... now I wonder why there isn't a Truncation attribute for fixed-
>> point types?  Maybe nobody before Andreas ever thought they'd need
>> one.  Might be useful.  (Also Floor, Ceiling.)
>
> No, I wondered about that long ago.
>
>> A possible problem with the floating-point conversion solution is that
>> there may be cases where you lose accuracy---if, e.g., the largest
>> floating-point type and fixed-point systems supported on the machine
>> are both 64 bits.  Since a floating-point number needs room for an
>> exponent, it's possible to define a fixed-point type with more bits in
>> the integer part than can be represented in the mantissa of a floating-
>> point type, e.g.
>
> One must always be careful in such cases that the conversion will not fail 
> or lose important bits.

Right, in both cases. Sounds like someone should propose something on 
Ada-Comment. (This seems like the sort of small cleanup that could be added 
to the next Amendment.)

                            Randy.

Re: Modify value - type duration

[Ludovic Brenta]

Randy Brukardt wrote:
> Jeffrey R. Carter wrote:
> > Adam Beneschan wrote:
>
> >> Hmmm ... now I wonder why there isn't a Truncation attribute for fixed-
> >> point types?  Maybe nobody before Andreas ever thought they'd need
> >> one.  Might be useful.  (Also Floor, Ceiling.)
>
> > No, I wondered about that long ago.

There is even an Ada Issue from John English about this:
http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00060.TXT?rev=1.2

--
Ludovic Brenta.