mulh
Signed multiply high
Multiply the signed values in xs1 to xs2, and store the upper half of the result in xd. The lower half is thrown away.
If both the upper and lower halves are needed, it suggested to use the sequence:
mulh xdh, xs1, xs2 mul xdl, xs1, xs2 ---
Microarchitectures may look for that sequence and fuse the operations.
| 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);
}
Bits<1> xs1_sign_bit = X[xs1][xlen() - 1];
Bits<MXLEN `* 2> src1 = {{xlen(){xs1_sign_bit}}, X[xs1]};
Bits<1> xs2_sign_bit = X[xs2][xlen() - 1];
Bits<MXLEN `* 2> src2 = {{xlen(){xs2_sign_bit}}, X[xs2]};
X[xd] = (src1 * src2)[(xlen() * 8'd2) - 1:xlen()];{
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
}
}