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CLMUL instruction set

Extension to the x86 instruction set From Wikipedia, the free encyclopedia

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Carry-less Multiplication (CLMUL) is an extension to the x86 instruction set used by microprocessors from Intel and AMD which was proposed by Intel in March 2008[1] and made available in the Intel Westmere processors announced in early 2010. Mathematically, the instruction implements multiplication of polynomials over the finite field GF(2) where the bitstring represents the polynomial . The CLMUL instruction also allows a more efficient implementation of the closely related multiplication of larger finite fields GF(2k) than the traditional instruction set.[2]

One use of these instructions is to improve the speed of applications doing block cipher encryption in Galois/Counter Mode, which depends on finite field GF(2k) multiplication. Another application is the fast calculation of CRC values,[3] including those used to implement the LZ77 sliding window DEFLATE algorithm in zlib and pngcrush.[4]

ARMv8 also has a version of CLMUL. SPARC calls their version XMULX, for "XOR multiplication".

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New instructions

The instruction computes the 128-bit carry-less product of two 64-bit values. The destination is a 128-bit XMM register. The source may be another XMM register or memory. An immediate operand specifies which halves of the 128-bit operands are multiplied. Mnemonics specifying specific values of the immediate operand are also defined:

More information Instruction, Opcode ...

A EVEX vectorized version (VPCLMULQDQ) is seen in AVX-512.

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CPUs with CLMUL instruction set

The presence of the CLMUL instruction set can be checked by testing one of the CPU feature bits.

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See also

References

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