How many times does this loop? mov cx, 5 mov bx, 0 L1: dec cx inc bx jnz L1
How many times does this loop? mov cx, 5 mov bx, 0 L1: dec cx inc bx jnz L1
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
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Transcribed Image Text:### Understanding Loop Execution in Assembly Language
In this example, we will analyze a simple loop written in Assembly language to determine how many times it executes.
```assembly
mov cx, 5 ; Initialize register CX with 5
mov bx, 0 ; Initialize register BX with 0
L1: ; Label L1
dec cx ; Decrement CX by 1
inc bx ; Increment BX by 1
jnz L1 ; Jump to L1 if CX is not zero
```
#### Explanation:
1. **Initialization**:
- The instruction `mov cx, 5` sets the register `CX` to 5.
- The instruction `mov bx, 0` sets the register `BX` to 0.
2. **Loop Execution**:
- The label `L1` marks the beginning of the loop.
- The instruction `dec cx` decrements the value in `CX` by 1.
- The instruction `inc bx` increments the value in `BX` by 1.
- The instruction `jnz L1` checks if `CX` is not zero; if true, it jumps back to label `L1`. If `CX` is zero, the loop terminates.
3. **Iteration Count**:
- The loop continues until the value in `CX` is decremented to zero. Since `CX` starts at 5 and is decremented by 1 in each iteration, the loop executes 5 times.
- During each iteration, `BX` is incremented by 1.
After 5 iterations, `CX` will be 0, causing the `jnz L1` instruction to fail its condition and terminate the loop. At this point, `BX` will have been incremented from 0 to 5.
#### Conclusion:
The loop executes **5 times**.
By understanding the flow of this simple Assembly loop, one can gain insights into the basic operation of loops in low-level programming.
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