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Re: Qt

From: Mark H Weaver
Subject: Re: Qt
Date: Thu, 10 Oct 2013 18:19:09 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux)

Andreas Enge <address@hidden> writes:

> On Thu, Oct 10, 2013 at 03:09:09PM +0200, Ludovic Courtès wrote:
>> Andreas Enge <address@hidden> skribis:
>> > I do not know how much this slows down qt applications. According to 
>> > wikipedia,
>> > sse2 arrived in 2001. So one could argue that adding it would exclude 
>> > almost
>> > no machines.
>> Yes, you may be right for SSE2 (especially considering the fact that
>> this kind of software is typically used on fairly recent machines.)
> Finally, I disabled everything special.

You can assume SSE2 on x86_64, as _all_ x86_64 processors have it.  In
fact, the C function calling conventions of SysV x86_64 psABI (used by
GNU/Linux) specify that the SSE2 registers are used for passing floating
point values as arguments.

> As this is not a number crunching library, I would like to be
> convinced of the usefulness of SSE.

Qt is not a number crunching library, but I suspect it _does_ have image
rendering code, where SIMD instruction sets such as SSE2 can make a
dramatic difference in performance.


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