Re: How to define HAVE_SSE42 with autotools?

[Anders Broman <anders.broman () ericsson com>]

-----Original Message-----
> From: wireshark-dev-bounces () wireshark org [mailto:wireshark-dev-bounces () wireshark org] On Behalf Of Guy Harris
> Sent: den 10 juni 2014 18:32
> To: Developer support list for Wireshark
> Subject: Re: [Wireshark-dev] How to define HAVE_SSE42 with autotools?
>
> HAVE_SSE42 is used in two places:
>
>       1) wsutil/ws_mempbrk_sse42.c, where it controls whether to build that file at all;
>
>       2) wsutil/ws_mempbrk.c, where it controls whether to check whether the CPU has SSE 4.2 and, if it does, call 
> the SSE 4.2 version of the code.
>
> So what HAVE_SSE42 really seems to mean is "does the compiler support the intrinsics used in 
> wsutil/ws_mempbrk_sse42.c?"
>
> Should we, instead, check for compiler support for those intrinsics?

Yes I guess...

> And will the compiler generate code for those intrinsics, using the SSE 4.2 instructions, even if you haven't told it, 
> with a command-line option, to generate SSE 4.2 code in general?  Or does the >compiler not do a good job of 
> supporting choosing whether to use SSE 4.2 instructions at run time rather than at compile time?

I have recently added some macros I found that define HAVE_SSE4_2 so at least the stuff compiles now on all the 
buildbots(I think).

I'm not sure if there should be a command line option or not. But ideally we should compile ws_mempbrk_sse42.c if the 
compiler supports it and check cpu_info() at runtime to use it or not.

Regards
Anders
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