Re: AMD64 and EM64T instruction sets.

From: Dennis Landi (nada_at_nada.com)
Date: 02/25/05 

Date: Fri, 25 Feb 2005 06:14:24 -0500

"Dennis" <marianndkc@home3.gvdnet.dk> wrote in message
news:421efa83$1@newsgroups.borland.com...
> Hi Per
>
> > Hmm - according to the second one there, old-style x87 instructions are
> not
> > supported in 64-bit mode. That's news to me. I guess it's all SSE now,
> then.
>
> I cannot belive that. SSE has no support for extended precision or Sin,
Cos,
> Log etc. Then it is impossible to develop scientific applications.
>
> > That means more work for the compiler porters than would otherwise have
> been
> > the case, but I guess the good news is that then they'll have an
> opportunity
> > to improve the quality of the output code.
>
> Quality of calculations will decrease, because of less precision. Speed
can
> increase, because of less precision and possibility of running two single
> precision SSE calculations in parallel in the extended precision pipeline.
> Code will be of same quality.
>

Here is a quote from Chapter 10 of the Optimization guide I referred to in
my msg to Per.

<quote>
AMD Athlon™ 64 and AMD Opteron™ processors support multiple methods of
performing
floating-point operations. They support the older x87 assembly instructions
in addition to the more
recent SIMD instructions (SSE, SSE2, and 3DNow!™ technologies). Many of the
suggestions in this
chapter are also generally applicable to the AMD Athlon 64 and AMD Opteron
processors, with the
exception of SSE2 optimizations and expanded register usage.
AMD Athlon 64 and AMD Opteron processors are 64-bit processors that are
fully backwards
compatible with 32-bit code. In general, 64-bit operating systems support
the x87 and 3DNow!
instructions in 32-bit threads; however, 64-bit operating systems may not
support x87 and 3DNow!
instructions in 64-bit threads. To make it easier to later migrate from
32-bit to 64-bit code, you may
want to avoid x87 and 3DNow! instructions altogether and use only SSE and
SSE2 instructions when
writing new 32-bit code.
</quote>

-- d
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