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From: Ole-Hjalmar Kristensen
 <ole-hjalmar.kristensen@substitute_employer_here.com>
Newsgroups: comp.lang.ada
Subject: Re: shifting bits
Date: 30 Aug 2004 11:03:51 +0200
Organization: Sun Microsystems
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>>>>> "fdf" == fabio de francesco <fmdf@tiscali.it> writes:

    fdf> Hello.
    fdf> I had to pack/unpack some variables into/from one. In order to get the
    fdf> result I chose to shift the variables' bits using multiplications and
    fdf> divisions by powers of two.

    fdf> 1) Does Ada have a built-in shift operand like C++ "<<" and ">>" ?

Yes, defined for modular types.

    fdf> 2) Can only variables of modular type be shifted ? If yes, why ?

Portability, I guess. What happens if you shift a sigend type? If this
annoys you, you can always convert to an unsigned type.

    fdf> 3) Will the following code produce some "shl" and "shr" machine
    fdf> instruction ?

    fdf> date_y := date_y * 2**9;	-- shift left	
    fdf> year := integer((date / 2**9) and offset_year); --shift right and
    fdf> "and" offset

    fdf> I thank you all in advance.

    fdf> Ciao,
    fdf> Fabio De Francesco.

Have you considered just using a record and specifying which bits
should be allocated to the different fields instead? This would save
you the trouble of doing the packing/unpacking yourself....


<snip>

-- 
   C++: The power, elegance and simplicity of a hand grenade.