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42 lines
2.2 KiB
Markdown
42 lines
2.2 KiB
Markdown
# Section 1 / Chapter 3 / While Loops
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## Overview
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We have already [covered](../if/README.md) 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.
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To illustrate this, here is a flow chart of an `if` statement (on the left) compared to a `while` loop (on the right).
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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").
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A new label is placed before evaluating the "Decision".
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A new unconditional branch is placed after the end of the "Code Block."
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For review, here is the assembly language for an `if` statement:
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```asm
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// Assume value of a is in x0 // 1
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// Assume value of b is in x1 // 2
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cmp x0, x1 // 3
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ble 1f // 4
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// CODE BLOCK // 5
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1: // 6
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```
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Here is the code for the `while` showing one new label and one new unconditional branch:
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```asm
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// Assume value of a is in x0 // 1
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// Assume value of b is in x1 // 2
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// 3
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1: cmp x0, x1 // 4
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ble 2f // 5
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// CODE BLOCK // 6
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b 1b // 7
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// 8
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2: // 9
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```
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Temporary label `2` on `line 9` takes the place of the line after the closing brace in a `while` loop.
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