CLMUL

Carry-less Multiply

CLMUL rd, rs1, rs2

Performs carry-less multiplication of the lower bits of rs1 and rs2. Used for CRC and GCM (crypto).

Encoding

Binary Layout

0000101

31:25

rs2

24:20

rs1

19:15

001

14:12

rd

11:7

0110011

6:0

 

Format R-Type

Opcode 0x0A001033

Extension Zbc

Operands

• rd
  Destination register (integer)
• rs1
  Source register 1 (integer)
• rs2
  Source register 2 (integer)

Example

CLMUL x10, x11, x12

// Carry-less multiply (GF(2^n)).

Related

More in Zbc

Reference

View in RISC-V Unprivileged ISA Specification ↗ RISC-V ISA Manual

Description

CLMUL performs carry-less multiplication of rs1 and rs2, writing the lower XLEN bits of the carry-less product to rd. Used in GF(2^n) arithmetic and CRC computation.

Operation

R[rd] = clmul(R[rs1], R[rs2]);