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From: Christopher Browne <cbbrowne@acm.org>
Newsgroups: comp.lang.ada
Subject: Re: if X in 1..35000 versus Boolean
Date: 13 Jul 2002 16:44:21 GMT
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Date: 2002-07-13T16:44:21+00:00
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The world rejoiced as Jan Prazak <janp9@gmx.net> wrote:
> Hello,
>
> I have a simple question:
>
> does the compiler (I am using GNAT) "see", that
> 	if X in 1..35000 then
>
> is the same as
> 	if (X >= 1) and (X <= 35000) then
>
> ???
>
> Or does the compiler really create an enumeration type with 35000 entries
> with values from 1 to 35000, just to check if X is in there???

I just changed a "if (fsm < proposal) and ..otherstuff.."  to "if (fsm
in 1..proposal) and ...otherstuff..." in a prime number sieve.

The size of the object code increased by 20 bytes, so it evidently
changed _something_.  I'll bet that it created an anonymous
enumeration type, and that some extra code is describing/referencing
that.

But it appears that optimization does The Right Thing so that the
result amounts to "X in 1..35000" ultimately being transformed into
something rather resembling "(X >= 1) and (X <= 35000)".
-- 
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