EBX (Extended Base Index) is commonly used to store the starting address of an array.
EBX, in the context of x86 architecture, serves multiple purposes, but its primary and most widely recognized usage is to act as a base register for memory addressing, especially when dealing with arrays or data structures. Let's explore this further:
Role of EBX
- Base Addressing: EBX often holds the base address of a data structure, like an array. This allows efficient access to elements within the array by using an offset from this base address.
Usage Example: Array Access
Imagine you have an array of integers stored in memory. The starting address of this array can be loaded into EBX. To access a specific element, you would add an offset to the value in EBX. For example:
; Assume EBX contains the starting address of an array of integers (4 bytes each).
; To access the 3rd element (index 2):
mov eax, [ebx + 8] ; Move the value at the address (EBX + 8) into EAX.
; (index 2 * 4 bytes/integer = 8)
In this example, [ebx + 8]
calculates the memory address of the third element, and the mov
instruction retrieves the integer stored at that address and places it into the EAX
register.
General Purpose Register
While EBX is often used for array addressing, it's essential to remember that it's a general-purpose register. This means it can also be used for other operations, such as:
- Storing intermediate calculation results.
- Holding function arguments.
- Performing general data manipulation.
However, its conventional role in holding base addresses makes it a valuable tool for working with structured data in assembly language.