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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Implementing an Ada compiler and libraries.
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	<464239b2_4@news.bluewin.ch>
	<20070510173440.6b5954ac@cube.tz.axivion.com>
	<87wszgocrj.fsf@ludovic-brenta.org>
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Date: Thu, 10 May 2007 18:49:09 +0200
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Date: 2007-05-10T18:49:09+02:00
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Stefan Bellon writes:
> Ludovic Brenta wrote:
>
>> Stefan Bellon writes:
>> > Gautier wrote:
>> >
>> >> - time stamps to check need of recompilations
>> >
>> > I've always wondered about the focussing on time stamps. I think
>> > the way to do it would be to calculate a hash sum (md5, sha1, ...)
>> > on the token stream without comments. This way you wouldn't have to
>> > recompile if you do layout and commentary changes, and even if you
>> > touch the file, you don't inadvertently trigger a recompilation.
>> 
>> That's what GNAT does, only it uses a simple checksum for performance
>> reasons.  Calculating the checksum and comparing it with the one in
>> the library (.ali files in the case of GNAT) has to be faster than
>> recompiling the file.
>
> But timestamps are considered as well. If you touch a file without
> modifying it otherwise, it triggers a recompilation.

Not in my experience.  Changing the timestamp causes a recalculation
of the checksum, that's all.  Even after adding whitespace or
pretty-printing the file, there is no recompilation.

-- 
Ludovic Brenta.