clmul

Carry-less multiply (low-part)

This instruction is defined by:

Encoding

Synopsis

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

Access

M	HS	U	VS	VU
Always	Always	Always	Always	Always

Always

Decode Variables

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

Execution

Pruned, XLEN == 64
Original

XReg xs1_val = X[xs1];
XReg xs2_val = X[xs2];
XReg output = 0;
for (U32 i = 0; i < 8'64; i++) {
  output = (((xs2_val >> i) & 1) == 1) ? output ^ (xs1_val << i) : output;
}
X[xd] = output;

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;