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From: Richard Henderson <rth@redhat.com>
To: elfutils-devel@lists.fedorahosted.org
Subject: Re: [PATCH 2/3] Simplify and inline get_uleb128 and get_sleb128
Date: Wed, 23 Apr 2014 08:27:11 -0700
Message-ID: <5357DBCF.70904@redhat.com>
In-Reply-To: m2zjjcpcye.fsf@redhat.com

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On 04/23/2014 03:17 AM, Petr Machata wrote:
> Wouldn't something like this get us off the hook as well?
> =

> -	(var) |=3D (typeof (var)) __s.i << ((nth) * 7);			      \
> +	(var) |=3D (typeof (var))						      \
> +	  (((uint64_t) (typeof (var)) __s.i) << ((nth) * 7));		      \
> =

> We are really only using the bitfield trick to avoid having to
> sign-extend by hand, but we can shift unsigned without losing anything.

It gets us off the hook, but might introduce a 64-bit shift where
only a 32-bit shift was required.

Sadly, (unsigned typeof(var)) doesn't work.  ;-)

But I gave the multiplication change a look, and the compiler is in fact
optimizing the multiplication by a power of 2 back into a shift.


r~

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