* can Ada give run-time error or warning for integer division with non-zero remainder?
@ 2012-08-12 1:14 Nasser M. Abbasi
2012-08-12 5:45 ` J-P. Rosen
` (3 more replies)
0 siblings, 4 replies; 6+ messages in thread
From: Nasser M. Abbasi @ 2012-08-12 1:14 UTC (permalink / raw)
In Ada when dividing 2 integers, the result is an integer
with the remainder ignored. Hence 3/2 gives 1
----------------------------------
with Ada.Integer_Text_IO ; use Ada.Integer_Text_IO ;
procedure foo4 is
N : constant integer := 3;
M : integer;
begin
M := N/2;
put(M);
end foo4;
--------------------------
>gnatmake foo4.adb
>./foo4
1
Now, suppose I want to know that a division between 2 integers
has resulted in nonzero remainder that was thrown away. May be
because my algorithm is meant to work only for even values and
an odd value means there was a bug somewhere and I want to
know about it.
Is there any kind of run-time switch to tell it to
check for this? I know I can always add logic myself to
check for this in the code, using rem() for example (which
might be the better solution actually) but I was just
wondering if there is a run-time switch for this.
thanks,
-Nasser
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: can Ada give run-time error or warning for integer division with non-zero remainder?
2012-08-12 1:14 can Ada give run-time error or warning for integer division with non-zero remainder? Nasser M. Abbasi
@ 2012-08-12 5:45 ` J-P. Rosen
2012-08-12 6:45 ` Dmitry A. Kazakov
` (2 subsequent siblings)
3 siblings, 0 replies; 6+ messages in thread
From: J-P. Rosen @ 2012-08-12 5:45 UTC (permalink / raw)
Le 12/08/2012 03:14, Nasser M. Abbasi a �crit :
>
> In Ada when dividing 2 integers, the result is an integer
> with the remainder ignored. Hence 3/2 gives 1
> [...]
> Is there any kind of run-time switch to tell it to
> check for this? I know I can always add logic myself to
> check for this in the code, using rem() for example (which
> might be the better solution actually) but I was just
> wondering if there is a run-time switch for this.
>
Fortunately not!
Dividing integers uses the integer division. If you want something else,
don't use integer division.
Having the outcome of an operation depend on a switch would imply that
you cannot predict the result of a program by reading it!
--
J-P. Rosen
Adalog
2 rue du Docteur Lombard, 92441 Issy-les-Moulineaux CEDEX
Tel: +33 1 45 29 21 52, Fax: +33 1 45 29 25 00
http://www.adalog.fr
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: can Ada give run-time error or warning for integer division with non-zero remainder?
2012-08-12 1:14 can Ada give run-time error or warning for integer division with non-zero remainder? Nasser M. Abbasi
2012-08-12 5:45 ` J-P. Rosen
@ 2012-08-12 6:45 ` Dmitry A. Kazakov
2012-08-12 7:16 ` Per Sandberg
2012-08-12 14:19 ` Robin Vowels
3 siblings, 0 replies; 6+ messages in thread
From: Dmitry A. Kazakov @ 2012-08-12 6:45 UTC (permalink / raw)
On Sat, 11 Aug 2012 20:14:42 -0500, Nasser M. Abbasi wrote:
> In Ada when dividing 2 integers, the result is an integer
> with the remainder ignored. Hence 3/2 gives 1
>
> ----------------------------------
> with Ada.Integer_Text_IO ; use Ada.Integer_Text_IO ;
>
> procedure foo4 is
> N : constant integer := 3;
> M : integer;
>
> begin
> M := N/2;
> put(M);
>
> end foo4;
> --------------------------
>
>>gnatmake foo4.adb
>>./foo4
> 1
> Now, suppose I want to know that a division between 2 integers
> has resulted in nonzero remainder that was thrown away. May be
> because my algorithm is meant to work only for even values and
> an odd value means there was a bug somewhere and I want to
> know about it.
It is not integer division then. You could use integer interval division
instead: [3, 3] / [2, 2] = [1, 2].
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: can Ada give run-time error or warning for integer division with non-zero remainder?
2012-08-12 1:14 can Ada give run-time error or warning for integer division with non-zero remainder? Nasser M. Abbasi
2012-08-12 5:45 ` J-P. Rosen
2012-08-12 6:45 ` Dmitry A. Kazakov
@ 2012-08-12 7:16 ` Per Sandberg
2012-08-12 14:03 ` Brad Moore
2012-08-12 14:19 ` Robin Vowels
3 siblings, 1 reply; 6+ messages in thread
From: Per Sandberg @ 2012-08-12 7:16 UTC (permalink / raw)
If you want an new behaviour for "/" on an integer type you could always
make a new integer type with the required properties:
-------------------------------------------------------------------------
package Integers is
type Integer is new Standard.Integer;
overriding function "/" (L : Integer; R : Integer) return Integer;
function "/" (L : Standard.Integer; R : Integer) return Integer;
function "/" (L : Integer; R : Standard.Integer) return Integer;
end Integers
-------------------------------------------------------------------------
package body Integers is
overriding function "/" (L : Integer; R : Integer) return Integer is
begin
return Ret : Integer do
Ret := Integer (Standard.Integer (Standard.Integer (L) /
Standard.Integer (R))); if Ret * R /= L then
raise Constraint_Error with L'Img & "/" & R'Img & " gives
reminder."; end if;
end return;
end "/";
function "/" (L : Standard.Integer; R : Integer) return Integer is
begin
return Ret : Integer do
Ret := Integer (L) / R;
end return;
end "/";
function "/" (L : Integer; R : Standard.Integer) return Integer is
begin
return Ret : Integer do
Ret := L / Integer (R);
end return;
end "/";
end Integers;
-------------------------------------------------------------------------
/P
On Sat, 11 Aug 2012 20:14:42 -0500 "Nasser M. Abbasi" <nma@12000.org>
wrote:
>
> In Ada when dividing 2 integers, the result is an integer
> with the remainder ignored. Hence 3/2 gives 1
>
> ----------------------------------
> with Ada.Integer_Text_IO ; use Ada.Integer_Text_IO ;
>
> procedure foo4 is
> N : constant integer := 3;
> M : integer;
>
> begin
> M := N/2;
> put(M);
>
> end foo4;
> --------------------------
>
> >gnatmake foo4.adb
> >./foo4
> 1
>
> Now, suppose I want to know that a division between 2 integers
> has resulted in nonzero remainder that was thrown away. May be
> because my algorithm is meant to work only for even values and
> an odd value means there was a bug somewhere and I want to
> know about it.
>
> Is there any kind of run-time switch to tell it to
> check for this? I know I can always add logic myself to
> check for this in the code, using rem() for example (which
> might be the better solution actually) but I was just
> wondering if there is a run-time switch for this.
>
> thanks,
> -Nasser
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: can Ada give run-time error or warning for integer division with non-zero remainder?
2012-08-12 7:16 ` Per Sandberg
@ 2012-08-12 14:03 ` Brad Moore
0 siblings, 0 replies; 6+ messages in thread
From: Brad Moore @ 2012-08-12 14:03 UTC (permalink / raw)
Or you could simplify this further using some new Ada 2012 features, and
eliminate the body.
package Integers is
type Integer is new Standard.Integer;
overriding function "/" (L : Integer; R : Integer) return Integer is
(Integer (Standard.Integer (L) / Standard.Integer (R)))
with Post => "/"'Result * R = L;
function "/" (L : Standard.Integer; R : Integer) return Integer is
(Integer (L / Standard.Integer (R)))
with Post => "/"'Result * R = Integer (L);
function "/" (L : Integer; R : Standard.Integer) return Integer is
(Integer (Standard.Integer (L) / R))
with Post => "/"'Result * Integer (R) = L;
end Integers;
Brad
On 12/08/2012 1:16 AM, Per Sandberg wrote:
> If you want an new behaviour for "/" on an integer type you could always
> make a new integer type with the required properties:
> -------------------------------------------------------------------------
> package Integers is
> type Integer is new Standard.Integer;
> overriding function "/" (L : Integer; R : Integer) return Integer;
> function "/" (L : Standard.Integer; R : Integer) return Integer;
> function "/" (L : Integer; R : Standard.Integer) return Integer;
> end Integers
> -------------------------------------------------------------------------
> package body Integers is
>
> overriding function "/" (L : Integer; R : Integer) return Integer is
> begin
> return Ret : Integer do
> Ret := Integer (Standard.Integer (Standard.Integer (L) /
> Standard.Integer (R))); if Ret * R /= L then
> raise Constraint_Error with L'Img & "/" & R'Img & " gives
> reminder."; end if;
> end return;
> end "/";
>
> function "/" (L : Standard.Integer; R : Integer) return Integer is
> begin
> return Ret : Integer do
> Ret := Integer (L) / R;
> end return;
> end "/";
>
> function "/" (L : Integer; R : Standard.Integer) return Integer is
> begin
> return Ret : Integer do
> Ret := L / Integer (R);
> end return;
> end "/";
>
> end Integers;
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: can Ada give run-time error or warning for integer division with non-zero remainder?
2012-08-12 1:14 can Ada give run-time error or warning for integer division with non-zero remainder? Nasser M. Abbasi
` (2 preceding siblings ...)
2012-08-12 7:16 ` Per Sandberg
@ 2012-08-12 14:19 ` Robin Vowels
3 siblings, 0 replies; 6+ messages in thread
From: Robin Vowels @ 2012-08-12 14:19 UTC (permalink / raw)
On Aug 12, 11:14 am, "Nasser M. Abbasi" <n...@12000.org> wrote:
> In Ada when dividing 2 integers, the result is an integer
> with the remainder ignored. Hence 3/2 gives 1
>
> ----------------------------------
> with Ada.Integer_Text_IO ; use Ada.Integer_Text_IO ;
>
> procedure foo4 is
> N : constant integer := 3;
> M : integer;
>
> begin
> M := N/2;
> put(M);
>
> end foo4;
> --------------------------
>
> >gnatmake foo4.adb
> >./foo4
>
> 1
>
> Now, suppose I want to know that a division between 2 integers
> has resulted in nonzero remainder that was thrown away. May be
> because my algorithm is meant to work only for even values and
> an odd value means there was a bug somewhere and I want to
> know about it.
Use MOD.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2012-08-12 1:14 can Ada give run-time error or warning for integer division with non-zero remainder? Nasser M. Abbasi
2012-08-12 5:45 ` J-P. Rosen
2012-08-12 6:45 ` Dmitry A. Kazakov
2012-08-12 7:16 ` Per Sandberg
2012-08-12 14:03 ` Brad Moore
2012-08-12 14:19 ` Robin Vowels
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