CLMUL instruction set

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. The purpose is to improve the speed of applications doing block cipher encryption in Galois/Counter Mode, which depends on finite field multiplication. Finite field (GF(2^k)) multiplication can be implemented more efficiently^[2] with the new CLMUL instructions than with the traditional instruction set^[3]

New instructions

Instruction	Description
PCLMULQDQ	Performs a carry-less multiplication of two 64-bit integers

PCLMULLQLQDQ xmmreg,xmmrm [rm: 66 0f 3a 44 /r 00]
PCLMULHQLQDQ xmmreg,xmmrm [rm: 66 0f 3a 44 /r 01]
PCLMULLQHQDQ xmmreg,xmmrm [rm: 66 0f 3a 44 /r 02]
PCLMULHQHQDQ xmmreg,xmmrm [rm: 66 0f 3a 44 /r 03]
PCLMULQDQ xmmreg,xmmrm,imm [rmi: 66 0f 3a 44 /r ib]

CPUs with CLMUL instruction set

• Intel
  • Westmere processor, March 2010.
• AMD:
  • Bulldozer processor, 2011^[4].

See also

• Finite field arithmetic
• AES instruction set
• FMA3 instruction set
• FMA4 instruction set
• AVX instruction set
• X86

References

1. ^ "Intel Software Network". Intel. http://softwareprojects.intel.com/avx/. Retrieved 2008-04-05. 
2. ^ "Intel Carry-Less Multiplication Instruction and its Usage for Computing the GCM Mode - Rev 2". http://software.intel.com/en-us/articles/intel-carry-less-multiplication-instruction-and-its-usage-for-computing-the-gcm-mode/. 
3. ^ Detailed description of instructions on Intel website
4. ^ Dave Christie (May 6, 2009). "Striking a balance". AMD Developer blogs. http://blogs.amd.com/developer/2009/05/06/striking-a-balance/. Retrieved 2011-03-11.