2.2 KiB
While Loops
Overview
We have already covered the if statement. A while loop is exactly the same with the addition of at least one branch and a 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 just before the evaluation of the boolean condition (the "Decision").
A new label is placed before evaluating the "Decision".
A 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 label 2 on line 9 takes the place of the line after the closing brace in a while loop.