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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: AI12-0218:  What is the portable representation clause for
 processing IETF packets on little-endian machines?
Date: Mon, 14 May 2018 17:54:52 -0500
Organization: JSA Research & Innovation
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Date: 2018-05-14T17:54:52-05:00
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"Paul Rubin" <no.email@nospam.invalid> wrote in message 
news:87lgcphdxq.fsf@nightsong.com...
> "Randy Brukardt" <randy@rrsoftware.com> writes:
>> I don't know of any way on the x86 processor of reading a byte-swapped
>> 32-bit integer into a register so it can be used.
>
> Load it into a register, then BSWAP.  This could be made into a compiler
> intrinsic if necessary.  GCC has __builtin_bswap16, __builtin_bswap32,
> and __builtin_bswap64 for this purpose.

What's "BSWAP"? It's not an instruction I'm familar with on x86. 
(Admittedly, I don't usually use newer instructions because of the need to 
have some sort of alternative to run on older processors.)

In any case, one has to build such support into the back-end. (Compiler 
front-ends are almost always target-independent.) "intrinsics" are just a 
fancy way of identifying things that are directly supported in the back-end.

                          Randy.