linux-kernel - Re: [PATCH] tcp_lp: use 64-bit arithmetic instead of 32-bit

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Message-ID: <20180201003236.06143fd0@alans-desktop>
Date:   Thu, 1 Feb 2018 00:32:36 +0000
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     "Wong Hoi Sing, Edison" <hswong3i@...il.com>,
        "Hung Hing Lun, Mike" <hlhung3i@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>
Subject: Re: [PATCH] tcp_lp: use 64-bit arithmetic instead of 32-bit

On Wed, 31 Jan 2018 18:24:07 -0600
"Gustavo A. R. Silva" <gustavo@...eddedor.com> wrote:

> Cast to s64 some variables and a macro in order to give the
> compiler complete information about the proper arithmetic to
> use. Notice that these elements are used in contexts that
> expect expressions of type s64 (64 bits, signed).
> 
> Currently such expression are being evaluated using 32-bit
> arithmetic.

The question you need to ask is 'can it overflow 32bit maths', otherwise
you are potentially making the system do extra work for no reason.

Alan