mulw

Signed 32-bit multiply

This instruction is defined by:

Encoding

Synopsis

Multiplies the lower 32 bits of the source registers, placing the sign-extension of the lower 32 bits of the result into the destination register.

Any overflow is thrown away.

In RV64, MUL can be used to obtain the upper 32 bits of the 64-bit product, but signed arguments must be proper 32-bit signed values, whereas unsigned arguments must have their upper 32 bits clear. If the arguments are not known to be sign- or zero-extended, an alternative is to shift both arguments left by 32 bits, then use MULH[[S]U].

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

Bits<32> src1 = X[rs1][31:0];
Bits<32> src2 = X[rs2][31:0];
Bits<32> result = src1 * src2;
Bits<1> sign_bit = result[31];
X[rd] = {{32{sign_bit}}, result};

if (implemented?(ExtensionName::M) && (CSR[misa].M == 1'b0)) {
  raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
}
Bits<32> src1 = X[rs1][31:0];
Bits<32> src2 = X[rs2][31:0];
Bits<32> result = src1 * src2;
Bits<1> sign_bit = result[31];
X[rd] = {{32{sign_bit}}, result};