Registerindirect

Register indirect is a computer architecture addressing mode in which the operand’s memory address is held in a register. The value stored at the memory location pointed to by that register is then used as the actual operand. This mode is common for implementing pointers and dynamic data structures, where the register serves as a pointer into memory.

In operation, an instruction specifies a register that contains the address of the data. The processor fetches or stores the operand from the memory location addressed by that register. For example, in some architectures you might see an instruction like mov eax, [ebx], which loads into eax the value stored at the memory address contained in ebx. An offset can also be added, such as mov eax, [ebx+4], to access data located at a fixed distance from the address in the register.

Variants of register indirect addressing include offset (displacement) forms and indexing, as well as post- or pre-increment/decrement of the address register. For instance, post-indexed addressing may adjust the register after the access (as in certain ARM or other ISAs), enabling compact pointer arithmetic. Pre-indexed forms combine the offset with the address modification in a single instruction.

Usage and performance considerations vary by architecture. Register indirect addressing provides flexibility for accessing arrays, structures, and dynamically allocated memory via pointers, but it tends to be slower than register-direct addressing due to the additional memory access. Efficient use relies on careful register allocation and awareness of potential cache effects.

---