From: Jeff King <peff@peff.net>
Date: Sat, 03 Dec 2016 05:21:04 GMT
Subject: Re: [PATCH 3/4] shallow.c: bit manipulation tweaks
Message-ID: <20161203052104.jbxhzpweupiaz7wi@sigill.intra.peff.net>
In-Reply-To: <1480710664-26290-3-git-send-email-rv@rasmusvillemoes.dk>

On Fri, Dec 02, 2016 at 09:31:03PM +0100, Rasmus Villemoes wrote:

> First of all, 1 << 31 is technically undefined behaviour, so let's just
> use an unsigned literal.

It took me a second to realize that you weren't talking about the
unsigned parameter here. You mean using "1U". It might be worth saying:

   ...use an unsigned literal, "1U".

to make it more obvious.

> If i is 'signed int' and gcc doesn't know that i is positive, gcc
> generates code to compute the C99-mandated values of "i / 32" and "i %
> 32", which is a lot more complicated than simple a simple shifts/mask.

Right, that makes sense (though it is a separate issue).

-Peff