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. 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".
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:
| Instruction | Opcode | Description |
|---|---|---|
PCLMULQDQ xmmreg,xmmrm,imm | [rmi: 66 0f 3a 44 /r ib] | Perform a carry-less multiplication of two 64-bit polynomials over the finite field GF(2)[X]. |
PCLMULLQLQDQ xmmreg,xmmrm | [rm: 66 0f 3a 44 /r 00] | Multiply the low halves of the two registers. |
PCLMULHQLQDQ xmmreg,xmmrm | [rm: 66 0f 3a 44 /r 01] | Multiply the high half of the destination register by the low half of the source register. |
PCLMULLQHQDQ xmmreg,xmmrm | [rm: 66 0f 3a 44 /r 10] | Multiply the low half of the destination register by the high half of the source register. |
PCLMULHQHQDQ xmmreg,xmmrm | [rm: 66 0f 3a 44 /r 11] | Multiply the high halves of the two registers. |
A EVEX vectorized version (VPCLMULQDQ) is seen in AVX-512.
CPUs with CLMUL instruction set
- Intel
- Westmere processor (March 2010).
- Sandy Bridge processor
- Ivy Bridge processor
- Haswell processor
- Broadwell processor (with increased throughput and lower latency[5])
- Skylake (and later) processor
- Goldmont processor
- AMD:
The presence of the CLMUL instruction set can be checked by testing one of the CPU feature bits.
See also
- Finite field arithmetic
- AES instruction set
- FMA3 instruction set
- FMA4 instruction set
- AVX instruction set
References
- ^ "Intel Software Network". Intel. Archived from the original on 2008-04-07. Retrieved 2008-04-05.
- ^ Shay Gueron; Michael E. Kounavis (2014-04-20). "Intel Carry-Less Multiplication Instruction and its Usage for Computing the GCM Mode – Rev 2.02" (PDF). Intel. Archived from the original on 2019-08-06.
- ^ "Fast CRC Computation for Generic Polynomials Using PCLMULQDQ" (PDF).
- ^ Vlad Krasnov (2015-07-08). "Fighting Cancer: The Unexpected Benefit Of Open Sourcing Our Code". CloudFlare. Retrieved 2016-09-04.
- ^ Johan De Gelas (2017-03-31). "The Intel Xeon E5 v4 Review: Testing Broadwell-EP With Demanding Server Workloads". Anandtech. p. 3.
- ^ "Slide detailing improvements of Jaguar over Bobcat". AMD. Retrieved August 3, 2013.
- ^ Dave Christie (6 May 2009). "Striking a balance". AMD Developer blogs. Archived from the original on 9 November 2013. Retrieved 2011-03-11.
