clmul

Carry-less multiply (low-part)

clmul produces the lower half of the 2*XLEN carry-less product

This instruction must have data-independent timing when extension Zkt is enabled.

Assembly format

clmul xd, xs1, xs2

Decode Variables

Bits<5> xs2 = $encoding[24:20];
Bits<5> xs1 = $encoding[19:15];
Bits<5> xd = $encoding[11:7];

Execution

if (implemented?(ExtensionName::B) && (CSR[misa].B == 1'b0)) {
  raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
}
XReg xs1_val = X[xs1];
XReg xs2_val = X[xs2];
XReg output = 0;
for (U32 i = 0; i < xlen(); i++) {
  output = (((xs2_val >> i) & 1) == 1) ? output ^ (xs1_val << i) : output;
}
X[xd] = output;

Exceptions

This instruction may result in the following synchronous exceptions:

  • IllegalInstruction

Encoding

svg

Defining extension

(Zbc || Zbkc)

Access

M

Always

Containing profiles

  • Mandatory: None

  • Optional: None