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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: Bit manipulation
Date: 2000/11/13
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In article <slrn90vsv1.l5.lutz@taranis.iks-jena.de>,
  lutz@iks-jena.de (Lutz Donnerhacke) wrote:
> This piece of code is from my play and experimental grounds.
> I'd prefer a portable solution instead of mapping maschine
> code into a portability lib.

No no no! Rotate_Left is a function defined IN THE ADA 95 RM,
it is a high level function that is defined at the Ada semantic
level. Yes, it will translate to some efficient sequence of
machine instructions (a single rotate instruction, where such
exists, some equivalent clever sequence where it does not).

There is absolutely NO need EVER to do roll-your-own rotates
in Ada 95.

As I say, this is not exactly obscure, if you look up rotate
in the RM index, you will find the reference.

One note here. In the RM, Rotate_Left and Rotate_Right are
defined only on the types in Interfaces, which is a bit
limiting, but for portability across compilers you have to
stick to this.

In GNAT, we permit the definition of an intrinsic (using
pragma Import (Intrinsic,Rotate_xxx)) Rotate_Left/Right for
any user defined modular type, but this is not necessarily
portable (this is actually something the ARG should add as
a recommended enhancement, since it is hard to imagine any
compiler would find it hard to do).


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