This work is created by Perry Kivolowitz, Professor and Chair of Computer Science at Carthage College. It is copyright © 2021 and may be freely shared for educational purposes.
We have already covered the if statement. A while loop is exactly the same with the addition of one branch and one label. It really is that simple.
To illustrate this, here is a flow chart of an if statement (on the left) compared to a while loop (on the right).
The closing brace in an if statement is indicated by the red arrow head. This isn't a branch, the code flow simply falls through to the statement beyond the closing brace. In the while loop, the behavior of the closing brace changes to be that of a branch back to prior to the evaluation of a boolean condition (the "Decision").
The new label is placed before evaluating the "Decision". The new unconditional branch is placed after the end of the "Code Block."
For review, here is the assembly language for an if statement:
// Assume value of a is in x0 // 1
// Assume value of b is in x1 // 2
cmp x0, x1 // 3
ble 1f // 4
// CODE BLOCK // 5
1: // 6 Here is the code for the while showing one new label and one new unconditional branch:
// Assume value of a is in x0 // 1
// Assume value of b is in x1 // 2
// 3
1: cmp x0, x1 // 4
ble 2f // 5
// CODE BLOCK // 6
b 1b // 7
// 8
2: // 9 Temporary lable 2 on line 9 takes the place of the line after the closing brace in a while loop.