linux-kernel - Re: PATCH [0/3]: Simplify the kernel build by removing perl.

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Date:	Sun, 4 Jan 2009 02:36:09 +0000
From:	Jamie Lokier <jamie@...reable.org>
To:	Rob Landley <rob@...dley.net>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Leon Woestenberg <leon.woestenberg@...il.com>,
	Embedded Linux mailing list <linux-embedded@...r.kernel.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sam Ravnborg <sam@...nborg.org>
Subject: Re: PATCH [0/3]: Simplify the kernel build by removing perl.

Rob Landley wrote:
> This doesn't _need_ bignum support.  It maxes out around 72 bits and
> the _result_ can't use more than about $SHIFT bits because you're
> dividing by the amount you shifted, so just chop off the bottom 32
> bits, do a normal 64 bit division on the top (it has to fit), and
> then do the same division on the appropriate shifted remainder, and
> combine the results.  This is easy because when the shift _is_ 32
> bits or more, the bottom 32 bits all have to be zeroes so you don't
> even have to mask and add, just shift the remainder left 32 bits so
> you can continue the divide.
> 
> Pulling out perl isn't always a good alternative to thinking about
> the problem.

Related query:

Does the Perl script being replaced use 64-bit arithmetic?  Because
many Perl installations only do 32-bit arithmetic.

If the Perl version works in 32-bit arithmetic, why does the shell
version not do the same thing?

-- Jamie
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