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From: cet1@cl.cam.ac.uk (C.E. Thompson)
Newsgroups: comp.lang.ada
Subject: Re: how to do this in Ada?
Message-ID: <1811@gannet.cl.cam.ac.uk>
Date: 19 Mar 90 17:11:39 GMT
References: <256@avocado.uucp>
Sender: news@cl.cam.ac.uk
Reply-To: cet1@cl.cam.ac.uk (C.E. Thompson)
Organization: U of Cambridge Comp Lab, UK
List-Id: <comp.lang.ada>

In article <256@avocado.uucp> garym@sugar.hackercorp.com writes:
> ...
>The C compiler will probably generate a table jump.  But before it can index
>into the table it must make sure that the index is within the range 0..2, that
>takes 2 compares.  ...

A common fallacy. With any machine instruction set that you care to name,
you will find that you can test a value for being in the range a..b with 
an add/subtract and one compare (and subsequent conditional branch): usually
a subtract of 'a' and an unsigned comparison with 'b-a'. If a is zero, as
here, the subtract disappears as well.

Of course, this applies to the Ada range test as well.

Chris Thompson
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