Adding Numbers Using Pointers

Pointers to add numbers

Now, we’ll look at the next pseudocode statement:

[x1] <- [x1] + [x0]

Recall that [x0] and [x1] are the contents of memory cells whose addresses (locations) are stored in x0 and x1 CPU registers.

We look at how we add numbers by using pointers in the following languages:

In the C/C++ language

The expression [x1] <- [x1] + [x0] is equivalent to the following C/C++ language expression:

*pb = *pb + *pa;

In this expression, the * operator is an instruction to retrieve memory contents pointed to by the pointers pa or pb (also called pointer dereference).

In the assembly language

In the assembly language, we use the instruction add for the + operator, but we cannot use memory addresses in one-step instruction:

add [x1], [x0]      // invalid instruction

We can only use registers, and therefore, we need to employ two registers as temporary variables, as shown in the assembly pseudocode below: