mul
Signed multiply
MUL performs an XLEN-bitxXLEN-bit multiplication of xs1 by xs2 and places the lower
XLEN bits in the destination register.
Any overflow is thrown away.
| If both the high and low bits of the same product are required, then the recommended code sequence is: MULH[[S]U] xdh, xs1, xs2; MUL xdl, xs1, xs2 (source register specifiers must be in same order and xdh cannot be the same as xs1 or xs2). Microarchitectures can then fuse these into a single multiply operation instead of performing two separate multiplies. |
| This instruction must have data-independent timing when extension Zkt is enabled. |
Decode Variables
Bits<5> xs2 = $encoding[24:20];
Bits<5> xs1 = $encoding[19:15];
Bits<5> xd = $encoding[11:7];Execution
-
IDL
-
Sail
if (implemented?(ExtensionName::M) && (misa.M == 1'b0)) {
raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
}
XReg src1 = X[xs1];
XReg src2 = X[xs2];
X[xd] = (src1 * src2)[MXLEN - 1:0];{
if extension("M") | haveZmmul() then {
let rs1_val = X(rs1);
let rs2_val = X(rs2);
let rs1_int : int = if signed1 then signed(rs1_val) else unsigned(rs1_val);
let rs2_int : int = if signed2 then signed(rs2_val) else unsigned(rs2_val);
let result_wide = to_bits(2 * sizeof(xlen), rs1_int * rs2_int);
let result = if high
then result_wide[(2 * sizeof(xlen) - 1) .. sizeof(xlen)]
else result_wide[(sizeof(xlen) - 1) .. 0];
X(rd) = result;
RETIRE_SUCCESS
} else {
handle_illegal();
RETIRE_FAIL
}
}