Re: Restarting Tread: Why isn't this program working with Unchecked_Converstion

Re: Restarting Tread: Why isn't this program working with Unchecked_Converstion

[Martin]

On Jan 15, 8:53 pm, ChristopherL <clusard...@aol.com> wrote:
> I'm restarting the tread [How to put 200 into an integer sub-type of
> 16 bits (code included)] with a new subject because the last was too
> long!
>
> How can I be getting the below error message with
> "Unchecked_Conversion".
>
> Isn't Unchecked_conversion just suppose to copy bits?
>
> I want to copy bits from an Ada float to a user defined short integer
> maintaining the same bit representation.
>
> Arg:Float;  -- From this with a value of 200
> subtype Short_integer is Integer range -(2 ** 7) .. ((2 ** 7) - 1 );
> Result2: Short_integer; --to this, and I want to round Arg
>
> These 3 definitions of Arg and Result2 can not chanage.
>
> Arg will never be negative or greater than 200/201.
>
> Chris L.
>
> with Unchecked_Conversion;
>
> procedure test is
>   subtype Short_integer1 is Natural range 0.. ((2 ** 10) - 1);
>   subtype Short_integer2 is Integer range -(2 ** 7)..((2 ** 7) - 1);
>
>   subtype A_Float is Float;
>
>   subtype A_Natural is Natural range 0..((2 ** 8) - 1);
>   -- The next line of code (if used) gives compilation error message:
>   -- A_NATURAL does not denote a first subtype
>   -- for A_Natural'Size use Short_integer1'Size;
>
>   Size_Of_Float : integer := Float'Size;      --32 bits long
>
>   Size_Of_short_integer: integer := Short_integer1'Size;--10 bits
> long
>   Size_Of_short_int: integer := Short_integer2'Size;--10 bits long
>
>   Size_Of_Natural: integer := A_Natural'Size;       --8 bits long

Are you sure about those sizes? Try:

Put_Line ("Float'Size          =" & Integer'Image (Float'Size));
Put_Line ("Short_integer1'Size =" & Integer'Image
(Short_integer1'Size));
Put_Line ("Short_integer2'Size =" & Integer'Image
(Short_integer2'Size));
Put_Line ("Natural'Size        =" & Integer'Image (Natural'Size));

An aside - probably wasted if you don't understand subtypes and ranges
- but you don't have to assign everything to 'integer'. Instead you
can store the constants like this:

   Size_Of_Float : constant := Float'Size;

The benefit is that you can mix this into just about any expression
without having to bother about type conversions.

> Result2 := Get_Bits (Result1);

Result2 is of type Short_integer2 - which _you_ defined to be of the
range -128 to 127 (inclusive). Why are you surprised that 201 does
fit??? And that's assuming the Unchecked_Conversion works - double
check the actual sizes!

Cheers
-- Martin

Re: Restarting Tread: Why isn't this program working with Unchecked_Converstion

[tmoran]

On Jan 15, 3:20 pm, ChristopherL <clusard...@aol.com> wrote:
> On Jan 15, 5:24 pm, Martin <martin.do...@btopenworld.com> wrote:
>
> > And that's assuming the Unchecked_Conversion works - double
> > check the actual sizes!
>
> In the debugger when I look at Float'Size it tells me 32.
> When I look at Short_integer1'Size it tells me 10, and for
> Short_integer2'Size it tell me 10.
>
> Chris L.

An Unchecked_Conversion just copies bits.  There's no way to copy 32
bits into something with room for only 10, and the compiler is
pointing this out now.  I suppose it could copy the leftmost 5 of the
32 bits, and the rightmost 5, and let you try to debug the result, but
that isn't The Ada Way.
Why don't you simply do a type conversion
  Result2 := Short_Integer2 (Result1);
There will then be a run-time check and, if the value in Result1 will
fit in a Short_Integer2, the assignment will take place.  If it won't
fit, it will raise an exception so you can debug your program.

Re: Restarting Tread: Why isn't this program working with Unchecked_Converstion

[Martin]

On Jan 15, 11:20 pm, ChristopherL <clusard...@aol.com> wrote:
> On Jan 15, 5:24 pm, Martin <martin.do...@btopenworld.com> wrote:
>
> > And that's assuming the Unchecked_Conversion works - double
> > check the actual sizes!
>
> In the debugger when I look at Float'Size it tells me 32.
> When I look at Short_integer1'Size it tells me 10, and for
> Short_integer2'Size it tell me 10.

Ok, according the Bob Duff's explanation, that can happen.

BUT hopefully you can now see that this is NOT PORTABLE and that you
shouldn't rely on it - the next time you upgrade you compile (or
change it completely), this may not be the case.

Go and try the "GNAT GPL 2008" compiler on Windows from the ("GNAT
Libre" site) and you'll see this.

This is why using subtypes of Integer/Natural (their sizes are not
always the same - just like C!!) are avoided and why you need to use
your own types - see (lots of) other posts - if you want to be sure of
sizes.

This is the "Ada way". Don't fight it, it's easier but will require
you to stop thinking in C.

Cheers
-- Martin

Re: Restarting Tread: Why isn't this program working with Unchecked_Converstion

[Jeffrey R. Carter]

ChristopherL wrote:
> 
> procedure test is

> CONSTRAINT_ERROR raised in MAIN

Obviously this error is coming from Main, not from the posted code for Test. We 
are unable to assist you with the error in Main since you have not posted its 
code for us.

-- 
Jeff Carter
"Your mother was a hamster and your father smelt of elderberries."
Monty Python & the Holy Grail
06

Re: Restarting Tread: Why isn't this program working with Unchecked_Converstion

[Jeffrey R. Carter]

ChristopherL wrote:
> 
> I do not know what MAIN is. The only program that I compile, link, and
> run is this test routine!

Curious. What compiler are you using?

-- 
Jeff Carter
"Your mother was a hamster and your father smelt of elderberries."
Monty Python & the Holy Grail
06

Re: Restarting Tread: Why isn't this program working with Unchecked_Converstion

[Adam Beneschan]

On Jan 15, 12:53 pm, ChristopherL <clusard...@aol.com> wrote:
> I'm restarting the tread [How to put 200 into an integer sub-type of
> 16 bits (code included)] with a new subject because the last was too
> long!
>
> How can I be getting the below error message with
> "Unchecked_Conversion".
>
> Isn't Unchecked_conversion just suppose to copy bits?
>
> I want to copy bits from an Ada float to a user defined short integer
> maintaining the same bit representation.
>
> Arg:Float;  -- From this with a value of 200
> subtype Short_integer is Integer range -(2 ** 7) .. ((2 ** 7) - 1 );
> Result2: Short_integer; --to this, and I want to round Arg
>
> These 3 definitions of Arg and Result2 can not chanage.
>
> Arg will never be negative or greater than 200/201.
>
> Chris L.
>
> with Unchecked_Conversion;
>
> procedure test is
>   subtype Short_integer1 is Natural range 0.. ((2 ** 10) - 1);
>   subtype Short_integer2 is Integer range -(2 ** 7)..((2 ** 7) - 1);
>
>   subtype A_Float is Float;
>
>   subtype A_Natural is Natural range 0..((2 ** 8) - 1);
>   -- The next line of code (if used) gives compilation error message:
>   -- A_NATURAL does not denote a first subtype
>   -- for A_Natural'Size use Short_integer1'Size;
>
>   Size_Of_Float : integer := Float'Size;      --32 bits long
>
>   Size_Of_short_integer: integer := Short_integer1'Size;--10 bits
> long
>   Size_Of_short_int: integer := Short_integer2'Size;--10 bits long
>
>   Size_Of_Natural: integer := A_Natural'Size;       --8 bits long
>
>   Arg     : A_Float;
>   Result2 : Short_integer2;
>   Result1 : Short_integer1;
>
>   function Get_Bits is new Unchecked_Conversion (Source =>
>     Short_integer1, Target => Short_integer2);
>
> Begin
>
> Arg := 200.0;
>
> Result1 := Short_integer1(Arg + 0.5);  -- Result1 becomes 201
> Result2 := Get_Bits (Result1);

OK, I think I can help, but before that I want to be clear on
something.
Result2's subtype is defined with the range -128 .. 127, so Result2
will never have the value 200.  It might have the same bit pattern as
the number 200, but the actual value will be -56.  If you used an
instance of Text_IO.Integer_IO to print out Result2, the output would
have "-56" in it.  If that's not the result you want, then there's
still a lot of confusion going on that we need to clear up first.  But
if you want help in getting things so that Result2 will be -56, then
we can work on that.

The problem here is that in the Ada definition of assignment, the
value on the right side is converted to the subtype of the result, and
that conversion could result in CONSTRAINT_ERROR.  For some reason,
your compiler has decided that Short_Integer2 is 10 bits.  The
Unchecked_Conversion is converting a 10-bit integer to a 10-bit
integer, which basically means it doesn't do anything (just copying
the bits).  Then, the code has a 10-bit integer whose value is 200;
then it checks the value against the bounds of the range, -128..127,
and decides that the value is out of range.  Not all compilers would
behave this way.  Many compilers would notice that, since the result
of Get_Bits has subtype Short_Integer2 and the variable Result2 has
the same subtype Short_Integer2, no actual checking is necessary
(assuming the values are valid).  Your compiler appears to do the
check anyway.

I think you'll have to force the compiler to work with 8-bit types
instead of 10-bit types.  Since you can't put a 'Size clause on a
subtype of Integer, you'll need to declare new types:

   type Short_Integer1 is range 0 .. (2**8)-1;   --not (2**10)-1
   for Short_Integer1'Size use 8;

   type Short_Integer2 is range -(2**7) .. (2**7)-1;
   for Short_Integer2'Size use 8;

Or, if Short_Integer2 *has* to be a subtype, then declare a new type
with a different name, force its size to be 8, and do a type
conversion from that new type to Short_Integer2 afterwards.

If that still doesn't work, perhaps because your compiler doesn't know
how to avoid looking at the leftover 2 bits, you may have to do
something inelegant:

   if Result1 >= 128
     then Result2 := Result1 - 256
     else Result2 := Result1;
   end if;

By the way, you probably don't want to add 0.5 in this code:

  Result1 := Short_integer1(Arg + 0.5);  -- Result1 becomes 201

In some languages, when you convert a real to an integer, the language
truncates to the next lower integer, so the way you do rounding is to
add 0.5 and then do the conversion.  In Ada, though, converting a real
to an integer does the rounding.  So adding your own 0.5 is wrong and
will give the wrong results.

  Result1 := Short_Integer1 (Arg);

is I think what you want.

I hope this helps.

                                 -- Adam

Re: Restarting Tread: Why isn't this program working with Unchecked_Converstion

[Ludovic Brenta]

On Jan 16, 3:11 pm, ChristopherL <clusard...@aol.com> wrote:
> Thanks Adam, yours is a working solution, see below.
>
> Thanks everyone,
> Chris L.
>
> On Jan 15, 6:27 pm, Adam Beneschan <a...@irvine.com> wrote:
>
>
>
> > I think you'll have to force the compiler to work with 8-bit types
> > instead of 10-bit types.  Since you can't put a 'Size clause on a
> > subtype of Integer, you'll need to declare new types:
>
> >    type Short_Integer1 is range 0 .. (2**8)-1;   --not (2**10)-1
> >    for Short_Integer1'Size use 8;
>
> >    type Short_Integer2 is range -(2**7) .. (2**7)-1;
> >    for Short_Integer2'Size use 8;
>
> > Or, if Short_Integer2 *has* to be a subtype, then declare a new type
> > with a different name, force its size to be 8, and do a type
> > conversion from that new type to Short_Integer2 afterwards.
>
> with Unchecked_Conversion;
>
> with Integer_Text_IO ;
>
> procedure test is
>   type Short_integer1 is range 0.. ((2 ** 8) - 1);
>   for Short_Integer1'Size use 8;
>
>   subtype Short_integer2 is Integer range -(2 ** 7)..((2 ** 7) - 1);
>
>   type Short_Integer3 is range -(2**7) .. (2**7)-1;
>   for Short_Integer3'Size use 8;
>
>   subtype A_Float is Float;
>
>   subtype A_Natural is Natural range 0..((2 ** 8) - 1);
>   -- The next line of code (if used) gives compilation error message:
>   -- A_NATURAL does not denote a first subtype
>   -- for A_Natural'Size use Short_integer1'Size;
>
>   Size_Of_Float : integer := Float'Size;      --32 bits long
>
>   Size_Of_short_integer: integer := Short_integer1'Size;--10 bits
> long
>   Size_Of_short_int: integer := Short_integer2'Size;--10 bits long
>
>   Size_Of_Natural: integer := A_Natural'Size;       --8 bits long
>
>   Arg     : A_Float;
>   Result3 : Short_integer2;
>   Result2 : Short_integer3;
>   Result1 : Short_integer1;
>
>   function Get_Bits2 is new Unchecked_Conversion (Source =>
>     Short_integer1, Target => Short_integer3);
>
> Begin
>
> Arg := 200.0;
>
> Result1 := Short_integer1(Arg);  -- Result1 becomes 200
> Result2 := Get_Bits2 (Result1);
> Result3 := Short_integer2(Result2);
> Integer_Text_IO.Put ( Result3 ) ;
> End test;

OK, you've managed to change the floating-point value 200.0 into an
integer value of -56. The bit representations of these two values are
different. (That's because the explicit type conversion of Arg from
type Float to type Short_integer1 changes the representation to
preserve the value).

I'm curious to understand: why did you do that?

PS. I think you can simplify your code into:

declare
   type Unsigned_8 is mod 2 ** 8;
   for Unsigned_8'Size use 8;
   type Signed_8 is range - 2**7 .. 2**7 - 1;
   for Signed_8'Size use 8;
   function To_Signed_8 is new Ada.Unchecked_Conversion (Unsigned_8,
Signed_8);

   Arg : Float := 200.0;
   Result : Signed_8 := To_Signed_8 (Unsigned_8 (Arg));
begin
   Ada.Text_IO.Put (Signed_8'Image (Result));
end;

--
Ludovic Brenta.

Re: Restarting Tread: Why isn't this program working with Unchecked_Converstion

[Martin]

On Jan 16, 3:11 pm, Ludovic Brenta <ludo...@ludovic-brenta.org> wrote:
> On Jan 16, 3:11 pm, ChristopherL <clusard...@aol.com> wrote:
>
>
>
> > Thanks Adam, yours is a working solution, see below.
>
> > Thanks everyone,
> > Chris L.
>
> > On Jan 15, 6:27 pm, Adam Beneschan <a...@irvine.com> wrote:
>
> > > I think you'll have to force the compiler to work with 8-bit types
> > > instead of 10-bit types.  Since you can't put a 'Size clause on a
> > > subtype of Integer, you'll need to declare new types:
>
> > >    type Short_Integer1 is range 0 .. (2**8)-1;   --not (2**10)-1
> > >    for Short_Integer1'Size use 8;
>
> > >    type Short_Integer2 is range -(2**7) .. (2**7)-1;
> > >    for Short_Integer2'Size use 8;
>
> > > Or, if Short_Integer2 *has* to be a subtype, then declare a new type
> > > with a different name, force its size to be 8, and do a type
> > > conversion from that new type to Short_Integer2 afterwards.
>
> > with Unchecked_Conversion;
>
> > with Integer_Text_IO ;
>
> > procedure test is
> >   type Short_integer1 is range 0.. ((2 ** 8) - 1);
> >   for Short_Integer1'Size use 8;
>
> >   subtype Short_integer2 is Integer range -(2 ** 7)..((2 ** 7) - 1);
>
> >   type Short_Integer3 is range -(2**7) .. (2**7)-1;
> >   for Short_Integer3'Size use 8;
>
> >   subtype A_Float is Float;
>
> >   subtype A_Natural is Natural range 0..((2 ** 8) - 1);
> >   -- The next line of code (if used) gives compilation error message:
> >   -- A_NATURAL does not denote a first subtype
> >   -- for A_Natural'Size use Short_integer1'Size;
>
> >   Size_Of_Float : integer := Float'Size;      --32 bits long
>
> >   Size_Of_short_integer: integer := Short_integer1'Size;--10 bits
> > long
> >   Size_Of_short_int: integer := Short_integer2'Size;--10 bits long
>
> >   Size_Of_Natural: integer := A_Natural'Size;       --8 bits long
>
> >   Arg     : A_Float;
> >   Result3 : Short_integer2;
> >   Result2 : Short_integer3;
> >   Result1 : Short_integer1;
>
> >   function Get_Bits2 is new Unchecked_Conversion (Source =>
> >     Short_integer1, Target => Short_integer3);
>
> > Begin
>
> > Arg := 200.0;
>
> > Result1 := Short_integer1(Arg);  -- Result1 becomes 200
> > Result2 := Get_Bits2 (Result1);
> > Result3 := Short_integer2(Result2);
> > Integer_Text_IO.Put ( Result3 ) ;
> > End test;
>
> OK, you've managed to change the floating-point value 200.0 into an
> integer value of -56. The bit representations of these two values are
> different. (That's because the explicit type conversion of Arg from
> type Float to type Short_integer1 changes the representation to
> preserve the value).
>
> I'm curious to understand: why did you do that?
>
> PS. I think you can simplify your code into:
>
> declare
>    type Unsigned_8 is mod 2 ** 8;
>    for Unsigned_8'Size use 8;
>    type Signed_8 is range - 2**7 .. 2**7 - 1;
>    for Signed_8'Size use 8;
>    function To_Signed_8 is new Ada.Unchecked_Conversion (Unsigned_8,
> Signed_8);
>
>    Arg : Float := 200.0;
>    Result : Signed_8 := To_Signed_8 (Unsigned_8 (Arg));
> begin
>    Ada.Text_IO.Put (Signed_8'Image (Result));
> end;
>
> --
> Ludovic Brenta.

Or using nothing but pre-defined standard types:

with Ada.Text_IO;
with Ada.Unchecked_Conversion;
with Interfaces;
procedure Test is
   function To_Integer_8 is
     new Ada.Unchecked_Conversion (Source => Interfaces.Unsigned_8,
                                   Target => Interfaces.Integer_8);

   Arg : Float := 200.0;
   Result : Interfaces.Integer_8 := To_Integer_8
(Interfaces.Unsigned_8 (Arg));
begin
   Ada.Text_IO.Put (Interfaces.Integer_8'Image (Result));
end Test;

Re: Restarting Tread: Why isn't this program working with Unchecked_Converstion

[Ludovic Brenta]

ChristopherL wrote on comp.lang.ada:
> On Jan 16, 7:11 am, Ludovic Brenta wrote:
> >    type Signed_8 is range - 2**7 .. 2**7 - 1;
> >    for Signed_8'Size use 8;
>
> I didn't use the second line in my program! Without it, my system
> uses 10 bits for this. I'm going to use my solution for now.
>
> Also experimenting on my own, if I only make the below change the
> variable Result has a value of -62 and not as above (-56).
>
> --  type Short_integer1 is range 0.. ((2 ** 8) - 1);
> --  for Short_Integer1'Size use 8;
>
>   type Short_integer1 is mod 2 ** 8;
>   for Short_Integer1'Size use 8;
>
> What does the following line of code do? It's new to me and have to
> know!
>
> type Short_integer1 is mod 2 ** 8;

This declares a modular type as defined in ARM 3.5.4:

http://www.adaic.com/standards/05rm/html/RM-3-5-4.html

I'm still curious to know what you are trying to achieve with all
these conversions. As I pointed out, the result has neither the value
nor the bit representation of the floating-point argument.

--
Ludovic Brenta.

Re: Restarting Tread: Why isn't this program working with Unchecked_Converstion

[Martin]

On Jan 16, 5:08 pm, ChristopherL <clusard...@aol.com> wrote:
> On Jan 16, 7:11 am, Ludovic Brenta <ludo...@ludovic-brenta.org> wrote:
>
> >    type Signed_8 is range - 2**7 .. 2**7 - 1;
> >    for Signed_8'Size use 8;
>
> I didn't use the second line in my program! Without it, my system
> uses 10 bits for this. I'm going to use my solution for now.
>
> Also experimenting on my own, if I only make the below change the
> variable Result has a value of -62 and not as above (-56).
>
> --  type Short_integer1 is range 0.. ((2 ** 8) - 1);
> --  for Short_Integer1'Size use 8;
>
>   type Short_integer1 is mod 2 ** 8;
>   for Short_Integer1'Size use 8;
>
> What does the following line of code do? It's new to me and have to
> know!
>
> type Short_integer1 is mod 2 ** 8;
>
> Chris L.

"mod" indicates a 'modular' type - i.e. unsigned, with wrap-round
semantics (no exceptions). Analogous to C 'unsigned'. Useful for
masking - using 'and', 'or', etc.

If you want an unsigned 8-bit integer with those semantics, you can
use the predefined type Interfaces.Unsigned_8. The package
'Interfaces' name indicates that you are 'close to the metal' in some
why and you actually _care_ about the size of objects your
manipulating.

There is a very good Wikibook on Ada you know...

http://en.wikibooks.org/wiki/Ada_Programming

and in particular:

http://en.wikibooks.org/wiki/Ada_Programming/Types/mod

Cheers
-- Martin

Re: Restarting Tread: Why isn't this program working with Unchecked_Converstion

[Georg Bauhaus]

ChristopherL schrieb:
> On Jan 16, 7:11 am, Ludovic Brenta <ludo...@ludovic-brenta.org> wrote:
>>    type Signed_8 is range - 2**7 .. 2**7 - 1;
>>    for Signed_8'Size use 8;
> 
> I didn't use the second line in my program! Without it, my system
> uses 10 bits for this. 

Is it actually doing that or is it just the
debugger which says so?  You can always test
this with

   if Signed_8'Size = 10 then
     ...

> What does the following line of code do? It's new to me and have to
> know!
> 
> type Short_integer1 is mod 2 ** 8;
> 


Which text book are you using?  This should be covered
in every Ada text book in an early chapter.

Re: Restarting Tread: Why isn't this program working with Unchecked_Converstion

[Stuart]

"ChristopherL" <clusardi2k@aol.com> wrote in message 
news:83d19cd8-71ca-43c1-a3eb-05832290e565@r36g2000prf.googlegroups.com...

> I'm restarting the tread [How to put 200 into an integer sub-type of
> 16 bits (code included)] with a new subject because the last was too
> long!

<snip problem with Unchecked_Conversion>

> I want to copy bits from an Ada float to a user defined short integer
> maintaining the same bit representation.

As said many times before this is a very unclear statement of what you are 
really trying to do and it is resulting in a lot of confusion.  You really 
need to read through the replies in your previous thread - especially as you 
have re-introduced the confusion of bits and values again.

<snip code>

I will have another guess at what you might be trying to do and provide a 
solution:

procedure ada_main is
   -- Things the OP says can't be changed:
   -- The definitions of Arg and Result2 can not chanage.
  subtype A_Float is Float;
  subtype Short_integer2 is Integer range -(2 ** 7)..((2 ** 7) - 1);

  Arg     : A_Float;
  Result2 : Short_integer2;

  -- Some things the OP has still not made clear:
  -- 1) What he is really trying to achieve.
  -- 2) Whether he wants to copy bits or values.
  -- 3) How he thinks values of Arg greater than 127.0
  --    ought to be represented in an integer type with
  --    a range -128..127
  -- 4) How rounding should take place (round up, round down,
  --    round nearest)

  -- Because of OP insistence that the the definitions cannot be changed
  -- and the fact Short_integer2 is based on integer which is implementation
  -- defined using Unchecked_Conversion here would be even more dubious
  -- than usual.

  -- Assuming he is expecting whole number values in Arg and
  -- wants a value in Result2 that is unique over the range
  -- 0.0 .. 200.0 and is easily relatable to the original
  -- value of Arg.

  -- Declare a sub-type capable of supporting all values of Arg and
  -- the computations we want to do:
   subtype S is Short_integer2'base range -256..200;
     -- REQUIREMENT:  The lower bound of S must be such that
     -- Short_integer2'first-Short_integer'last-1 <= S'first <=
     -- -(max(Arg) + 1)
     -- The upper bound must be such that
     -- S'last >= max(Arg)

     -- NB the lower bound is chosen to control the underlying
     -- representation when Arg > Short_integer2'last

     -- Assumes the base type of Short_integer2 will allow this;
     -- compiler will complain if not.

     -- If the base type does not support the range, a suitable
     -- new type to do the integer based calculations will be needed
     -- and some explicit type conversions will have to be made.

   -- I can't be bothered to think of a meaningful name for the subtype!!

   Int_Arg : S; -- Holds the integer value of Arg.

   V : Short_integer2;
   pragma volatile(V);
      -- Just to force demonstration code to do something external
begin

   Arg := 200.0;  -- OP chosen test case!

   Int_Arg := S(Arg);
      -- Convert to an integer value using Ada default rounding.

   -- Resolve cases where the value is outside the range of Short_integer2
   if (Int_Arg > Short_integer2'last) then
      Result2 := Int_Arg + S'first;
      -- Given the user specified constraints on Arg and the definition
      -- of Short_integer2 this will not exceed constraints.
   else
      Result2 := Int_Arg;
   end if;

   V := Result2;
end ada_main;

-- 
Stuart 

Re: Restarting Tread: Why isn't this program working with Unchecked_Converstion

[sjw]

On Jan 16, 12:18 pm, "Stuart" <stu...@0.0> wrote:
> "ChristopherL" <clusard...@aol.com> wrote in message
>
> news:83d19cd8-71ca-43c1-a3eb-05832290e565@r36g2000prf.googlegroups.com...
>
> > I'm restarting the tread [How to put 200 into an integer sub-type of
> > 16 bits (code included)] with a new subject because the last was too
> > long!
>
> <snip problem with Unchecked_Conversion>
>
> > I want to copy bits from an Ada float to a user defined short integer
> > maintaining the same bit representation.

(I'm sorry to reply to Stuart's post rather than OP's, but Google
fails to show OP's posts at all! (perhaps there's a reason for that?))

Sorry to shout, Chris, but you CAN NOT FIT THE BITS OF A STANDARD
FLOAT INTO ANYTHING SMALLER!!! IF YOU WANT THE SAME BIT REPRESENTATION
YOU HAVE TO USE THE SAME NUMBER OF BITS!!!

The following is another way of achieving unchecked conversion - the
results on a little-endian machine (i686) are

 2.00000E+02 ->  0  0  72  67
 3.14159E+00 ->  219  15  73  64

with Ada.Numerics;
with Ada.Text_IO; use Ada.Text_IO;
with System.Storage_Elements;

procedure Foo is
   F : Float;
   A : System.Storage_Elements.Storage_Array (1 .. 4);
   for A'Address use F'Address;
   pragma Import (Ada, A);  -- prevent unwanted auto-initialisations
   function Image (B : System.Storage_Elements.Storage_Element) return
String
     renames System.Storage_Elements.Storage_Element'Image;
begin
   F := 200.0;
   Put_Line (Float'Image (F)
               & " -> "
               & Image (A (1))
               & " "
               & Image (A (2))
               & " "
               & Image (A (3))
               & " "
               & Image (A (4)));
   F := Ada.Numerics.Pi;
   Put_Line (Float'Image (F)
               & " -> "
               & Image (A (1))
               & " "
               & Image (A (2))
               & " "
               & Image (A (3))
               & " "
               & Image (A (4)));
end Foo;