<s>
Carry-less	O
Multiplication	O
(	O
CLMUL	B-Device
)	O
is	O
an	O
extension	O
to	O
the	O
x86	B-Operating_System
instruction	O
set	O
used	O
by	O
microprocessors	B-Architecture
from	O
Intel	O
and	O
AMD	O
which	O
was	O
proposed	O
by	O
Intel	O
in	O
March	O
2008	O
and	O
made	O
available	O
in	O
the	O
Intel	B-Device
Westmere	I-Device
processors	I-Device
announced	O
in	O
early	O
2010	O
.	O
</s>
<s>
The	O
CLMUL	B-Device
instruction	O
also	O
allows	O
a	O
more	O
efficient	O
implementation	O
of	O
the	O
closely	O
related	O
multiplication	O
of	O
larger	O
finite	O
fields	O
GF(2k )	O
than	O
the	O
traditional	O
instruction	O
set	O
.	O
</s>
<s>
One	O
use	O
of	O
these	O
instructions	O
is	O
to	O
improve	O
the	O
speed	O
of	O
applications	O
doing	O
block	O
cipher	O
encryption	O
in	O
Galois/Counter	B-Algorithm
Mode	I-Algorithm
,	O
which	O
depends	O
on	O
finite	O
field	O
GF(2k )	O
multiplication	O
.	O
</s>
<s>
Another	O
application	O
is	O
the	O
fast	O
calculation	O
of	O
CRC	O
values	O
,	O
including	O
those	O
used	O
to	O
implement	O
the	O
LZ77	B-Algorithm
sliding	O
window	O
DEFLATE	B-Algorithm
algorithm	O
in	O
zlib	B-Language
and	O
pngcrush	B-Language
.	O
</s>
<s>
ARMv8	O
also	O
has	O
a	O
version	O
of	O
CLMUL	B-Device
.	O
</s>
<s>
Instruction	O
Opcode	O
Description	O
PCLMULQDQ	B-Device
xmmreg	O
,	O
xmmrm	O
,	O
imm	O
[	O
rmi	O
:	O
66	O
0f	O
3a	O
44	O
/r	O
ib ]	O
Perform	O
a	O
carry-less	O
multiplication	O
of	O
two	O
64-bit	O
polynomials	O
over	O
the	O
finite	O
field	O
GF(2 )	O
 [ X ] 	O
.	O
</s>
<s>
PCLMULLQLQDQ	B-Device
xmmreg	O
,	O
xmmrm	O
[	O
rm	O
:	O
66	O
0f	O
3a	O
44	O
/r	O
00 ]	O
Multiply	O
the	O
low	O
halves	O
of	O
the	O
two	O
registers	O
.	O
</s>
<s>
PCLMULHQLQDQ	B-Device
xmmreg	O
,	O
xmmrm	O
[	O
rm	O
:	O
66	O
0f	O
3a	O
44	O
/r	O
01 ]	O
Multiply	O
the	O
high	O
half	O
of	O
the	O
destination	O
register	O
by	O
the	O
low	O
half	O
of	O
the	O
source	O
register	O
.	O
</s>
<s>
A	O
EVEX	O
vectorized	O
version	O
(	O
VPCLMULQDQ	O
)	O
is	O
seen	O
in	O
AVX-512	B-General_Concept
.	O
</s>
<s>
Westmere	B-Device
processor	O
(	O
March	O
2010	O
)	O
.	O
</s>
<s>
The	O
presence	O
of	O
the	O
CLMUL	B-Device
instruction	I-Device
set	I-Device
can	O
be	O
checked	O
by	O
testing	O
one	O
of	O
the	O
CPU	O
feature	O
bits	O
.	O
</s>
