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

Always

Decode Variables

Bits<5> rs2 = $encoding[24:20];
Bits<5> rs1 = $encoding[19:15];
Bits<5> rd = $encoding[11:7];

Execution

Pruned, XLEN == 64
Original

XReg rs1_val = X[rs1];
XReg rs2_val = X[rs2];
XReg output = 0;
for (U32 i = 0; i < 64; i++) {
  output = (((rs2_val >> i) & 1) == 1) ? output ^ (rs1_val << i) : output;
}
X[rd] = output;

if (implemented?(ExtensionName::B) && (CSR[misa].B == 1'b0)) {
  raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
}
XReg rs1_val = X[rs1];
XReg rs2_val = X[rs2];
XReg output = 0;
for (U32 i = 0; i < xlen(); i++) {
  output = (((rs2_val >> i) & 1) == 1) ? output ^ (rs1_val << i) : output;
}
X[rd] = output;