mulhu
Unsigned multiply high
This instruction is defined by:
Synopsis
Multiply the unsigned values in rs1 to rs2, and store the upper half of the result in rd. The lower half is thrown away.
If both the upper and lower halves are needed, it suggested to use the sequence:
mulhu rdh, rs1, rs2 mul rdl, rs1, rs2 ---
Microarchitectures may look for that sequence and fuse the operations.
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<XLEN * 8'd2> src1 = {{XLEN{1'b0}}, X[rs1]};
Bits<XLEN * 8'd2> src2 = {{XLEN{1'b0}}, X[rs2]};
X[rd] = (src1 * src2)[127:XLEN];
if (implemented?(ExtensionName::M) && (CSR[misa].M == 1'b0)) {
raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
}
Bits<XLEN * 8'd2> src1 = {{XLEN{1'b0}}, X[rs1]};
Bits<XLEN * 8'd2> src2 = {{XLEN{1'b0}}, X[rs2]};
X[rd] = (src1 * src2)[(XLEN * 8'd2) - 1:XLEN];