Re: Combining two MMX registers into one SSE register?

Rich Fife schrieb:

> Is there a way to combine two MMX registers into the low and high quad
> words of an SSE register without getting memory involved? MOVQ2DQ does
> a zero extend, unfortunately, or it would be easy.
>
> -- Rich Fife --

Yes, two MOVQ2DQ and one additional, temporary used xmm-register is
required:

MOVQ2DQ xmm0, mm0
MOVQ2DQ xmm1, mm1
PUNPCKLQDQ xmm0, xmm1 ; xmm0 = mm1:mm0

note from:
---------------------------------------------------------------------------
Software Optimization Guide
for AMD Athlon? 64 and AMD Opteron? Processors

9.7 Storing Floating-Point Data in MMX? Registers (page 209)

Rationale
Using MOVDQ2Q or MOVQ2DQ to shuffle integer data between MMX and XMM
registers is useful to relieve register pressure; however, doing so
with floating-point data can impact performance. The impact is greater
if the floating-point data is denormalized.
---------------------------------------------------------------------------

Guess you are aware of the fact, that windows-64 bans mmx/x87, due to
not saving/restoring mmx/x87-registers during context switch ;-(

- Gerd


.

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