one for unsigned (mulq) and one for two’s-complement (imulq) multiplication.For both of these instructions, one argument must be in register %rax, and theother is given as the instruction source operand.

The different shift instructions can specify the shift amount either asan immediate value or with the single-byte register %cl.

The source operand designates a value that is immediate, stored in a register,or stored in memory. The destination operand designates a location that is either aregister or a memory address. x86-64 imposes the restriction that a move instruc-tion cannot have both operands refer to memory locations. Copying a value fromone memory location to another requires two instructions—the first to load thesource value into a register, and the second to write this register value to the des-tination.

The most general form is shown at the bottomof the table with syntax Imm(rb,ri,s). Such a reference has four components: animmediate offset Imm, a base register rb, an index register ri, and a scale factors, where s must be 1, 2, 4, or 8. Both the base and index must be 64-bit registers.The effective address is computed as Imm + R[rb] + R[ri] . s.