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Re: avoid possible overflow?

From: Vladimir 'φ-coder/phcoder' Serbinenko
Subject: Re: avoid possible overflow?
Date: Tue, 16 Feb 2010 13:46:53 +0100
User-agent: Mozilla-Thunderbird (X11/20091109)

Carles Pina i Estany wrote:
> Hello,
> The common pattern when doing a search by bisection is something like:
> +      current = min + (max - min) / 2;
> Instead of the first natural idea:
> -      current = (max + min) / 2;
> To avoid overflows.
> In gettext/gettext.c it's used in the "incorrect" way. It's not a big
> problem since would happen only with .mo files with lot of strings, like
> number that int represents in that architecture divided by 2 (aprox
> aprox.).
> See the attached file for a patch if we want to patch.
You forgot to make the same change before the loop. But actually it
doesn't matter because overflow in this statement:
  internal_position = offsettranslation + position * 8;
is reached well before the overflow in bisecting. Anyway this
mattersonly for >4GiB files and unless we put videos in .po I don't see
how this limit would be reached. So I prefer readability and would
reject this patch.
> Else I would at least add a comment that we simplified because we
> consider that will not happen.
> Thanks,
> ------------------------------------------------------------------------
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> Grub-devel mailing list
> address@hidden

Vladimir 'φ-coder/phcoder' Serbinenko

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