creating a 16 bit value from 2 8 bit values in Ada

creating a 16 bit value from 2 8 bit values in Ada

[Mark]

Could someone show me how to concatenate the Hi and Lo components? 
The end result - obviously - would be a 16 bit value.  I've waded
through my ada books here and keep coming up short?


type SOME_TYPE is 
  record 
    Lo   : BYTE;
    Hi   : BYTE;
    X    : BOOLEAN;
  -- more stuff
end record;

for SOME_TYPE use
 record
  Lo at 0 range 0 .. 6;
  Hi at 0 range 7 .. 15;
  -- more stuff
end record;  

In an earlier post i made a reference to 'intrinsics' that might aid
in my objective, but that appears to be a tartan utility.

Re: creating a 16 bit value from 2 8 bit values in Ada

[Darren New]

Mark wrote:
> Could someone show me how to concatenate the Hi and Lo components?
> The end result - obviously - would be a 16 bit value.  I've waded

Wouldn't it be something along the lines of 
  result := lo + 256 * hi;
?

-- 
Darren New 
San Diego, CA, USA (PST). Cryptokeys on demand.
** http://home.san.rr.com/dnew/DNResume.html **
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Things to be thankful for, #37:
   No sausage was served at the Last Supper.

Re: creating a 16 bit value from 2 8 bit values in Ada

[John McCabe]

On Fri, 02 Aug 2002 02:07:24 GMT, Darren New <dnew@san.rr.com> wrote:

>Mark wrote:
>> Could someone show me how to concatenate the Hi and Lo components?
>> The end result - obviously - would be a 16 bit value.  I've waded
>
>Wouldn't it be something along the lines of 
>  result := lo + 256 * hi;

That's pretty much what I would have said! 

Re: creating a 16 bit value from 2 8 bit values in Ada

[Stephen Leake]

ma740988@pegasus.cc.ucf.edu (Mark) writes:

> Could someone show me how to concatenate the Hi and Lo components? 
> The end result - obviously - would be a 16 bit value.  I've waded
> through my ada books here and keep coming up short?

Others have pointed out ' lo + 256 * hi'. Another choice is:

type Double_Byte_Type is record
    Lo : Byte;
    Hi : Byte;
end record;
for Double_Byte_Type use record
    Lo at 0 range 0 .. 6;
    Hi at 0 range 7 .. 15;
end record;  
for Double_Byte_Type'size use 16;

function to_int_16 is new Ada.Unchecked_conversions
   (Source => Double_Byte_Type,
    Target => Interfaces.Unsigned_16);

type Some_Type is record
   Hi_Lo : Double_Byte_Type;
   -- more stuff
end record;


One advantage of this version is it should take no code. One drawback
is you have to get the byte-endianness right.

-- 
-- Stephe

Re: creating a 16 bit value from 2 8 bit values in Ada

[Kevin Krieser]

Mark wrote:
> Could someone show me how to concatenate the Hi and Lo components? 
> The end result - obviously - would be a 16 bit value.  I've waded
> through my ada books here and keep coming up short?
> 
> 
> type SOME_TYPE is 
>   record 
>     Lo   : BYTE;
>     Hi   : BYTE;
>     X    : BOOLEAN;
>   -- more stuff
> end record;
> 
> for SOME_TYPE use
>  record
>   Lo at 0 range 0 .. 6;
>   Hi at 0 range 7 .. 15;
>   -- more stuff
> end record;  


Sorry to be picky, but the above wouldn't work.  Byte wouldn't fit in 7 
bits.

If you have some unsigned 16 bit type, called something like unsigned16, 
you could just do a big_val := unsigned16(hi) * 256 + unsigned16(lo);



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Re: creating a 16 bit value from 2 8 bit values in Ada

[SteveD]

"Mark" <ma740988@pegasus.cc.ucf.edu> wrote in message
news:a5ae824.0208011740.7f2df9dc@posting.google.com...
> Could someone show me how to concatenate the Hi and Lo components?
> The end result - obviously - would be a 16 bit value.  I've waded
> through my ada books here and keep coming up short?
>
>
> type SOME_TYPE is
>   record
>     Lo   : BYTE;
>     Hi   : BYTE;
>     X    : BOOLEAN;
>   -- more stuff
> end record;
>
> for SOME_TYPE use
>  record
>   Lo at 0 range 0 .. 6;
>   Hi at 0 range 7 .. 15;
>   -- more stuff
> end record;
>
> In an earlier post i made a reference to 'intrinsics' that might aid
> in my objective, but that appears to be a tartan utility.

Re: creating a 16 bit value from 2 8 bit values in Ada (again)

[SteveD]

Sorry about my previous accidental send.

Here is how I would do it (the following compiles and runs on GNAT
3.14p-nt):

with Ada.Text_Io;
with Interfaces;
 use Interfaces;
procedure Test is

  function To_Unsigned_16( lsb, msb : Unsigned_8 ) return Unsigned_16 is
  begin
    return Shift_Left( Unsigned_16( msb ), 8 ) or Unsigned_16( lsb );
  end To_Unsigned_16;

begin
  Ada.Text_Io.Put_Line( Unsigned_16'IMAGE( To_Unsigned_16( 16#01#,
16#00# ) ) );
  Ada.Text_Io.Put_Line( Unsigned_16'IMAGE( To_Unsigned_16( 16#00#,
16#01# ) ) );
end Test;

SteveD

Re: creating a 16 bit value from 2 8 bit values in Ada

[Robert Dewar]

Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov> wrote in message news:<uwur96s19.fsf@gsfc.nasa.gov>...
 
> One advantage of this version is it should take no code. 

No, it is probably much less efficient, because it forces
things into memory.


> One drawback
> is you have to get the byte-endianness right.

A big drawback. This is definitely not the right approach.