AMD Typewriter x86 사용자 설명서

22007E/0—November 1999

PXOR      MM2, MM2       ;   0 | 0
MOVD      MM0, [ab]      ; 0 0 | b a
MOVD      MM1, [cd]      ; 0 0 | d c
PUNPCKLWD MM0, MM2       ; 0 b | 0 a
PUNCPKLWD MM1, MM2       ; 0 d | 0 c
PMADDWD   MM0, MM1       ; b*d | a*c

If the swapping of MMX register halves is necessary, use the
PSWAPD instruction, which is a new AMD Athlon 3DNow! DSP
e x t e n s i o n .   U s e   o f   t h i s   i n s t r u c t i o n   s h o u l d   o n ly   b e   fo r
AMD Athlon specific code. “PSWAPD MMreg1, MMreg2”
performs the following operation:

mmreg1[63:32] = mmreg2[31:0])
mmreg1[31:0] = mmreg2[63:32])

See the AMD Extensions to the 3DNow! and MMX Instruction Set
Manual, order #22466 for more usage information.

Otherwise, for blended code, which needs to run well on
AMD-K6 and AMD Athlon family processors, the following code
is recommended:

;MM1 = SWAP (MM0), MM0 destroyed
MOVQ

MM1, MM0

;make a copy

PUNPCKLDQ 

MM0, MM0

;duplicate lower half

PUNPCKHDQ

MM1, MM0

;combine lower halves

;MM1 = SWAP (MM0), MM0 preserved
MOVQ

MM1, MM0

;make a copy

PUNPCKHDQ 

MM1, MM1

;duplicate upper half

PUNPCKLDQ

MM1, MM0

;combine upper halves

Both examples accomplish the swapping, but the first example
should be used if the original contents of the register do not
need to be preserved. The first example is faster due to the fact
that the MOVQ and PUNPCKLDQ instructions can execute in
parallel. The instructions in the second example are dependent
on one another and take longer to execute.