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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: How do you bitwise operations in Ada '83 and '95
Date: Fri, 21 Jul 2006 20:03:09 +0100
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Date: 2006-07-21T20:03:09+01:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> It depends on endianness. Provided that storage elements are octets
> on both machines, which assumption could be wrong, 128 shifted left
> might yield 0, 256 or even 64 (what is "left"?).

You might as well argue that the C operator<< could produce 64 or 256.

> When considering *any* thinkable architecture, it might be even
> impossible to implement Shift_* at all. Let some crazy hardware
> store numbers in only odd bits, reserving even ones for something
> else (like a check-sum). On such imaginary hardware Shift_Left (*,
> 1) wouldn't even yield a valid number! Actually "they operate on a
> bit-by-bit basis" is quite hazy. What is bit? Which bits are
> adjacent? How are they ordered? What does "left" mean? Which bits
> are of the number? etc.

One would think the market for hardware like that would be pretty
thin; not really a "thinkable" architecture. Certainly not
interesting.