
Computer Networking: A Top-Down Approach (7th Edition)
7th Edition
ISBN: 9780133594140
Author: James Kurose, Keith Ross
Publisher: PEARSON
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Question
Modify the Extended_Add procedure add two 256-bit (32-byte) integers.

Transcribed Image Text:### Assembly Code Explanation
This assembly code snippet demonstrates a sequence of operations manipulating bytes and flags, often used for arithmetic operations and flag management.
#### Data Section:
- **val1 BYTE '8'**: Stores the ASCII character '8'.
- **val2 BYTE '9'**: Stores the ASCII character '9'.
#### Code Section:
1. **mov ah,0**: Initializes the `AH` register to 0.
- *Comment: `AX` = 0038h*
2. **mov al,val1**: Loads the ASCII value of '8' into the `AL` register.
- *Comment: Not explicitly listed but affects subsequent operations.*
3. **sub al,val2**: Subtracts the ASCII value of '9' from `AL`.
- *Comment: `AX` = 00FFh*
4. **aas**: ASCII adjust AL after subtraction; corrects the result in `AL` for BCD operations.
- *Comment: `AX` = FF09h*
5. **pushf**: Pushes the current state of the flags register onto the stack.
- *Comment: Save the Carry flag*
6. **or al,30h**: Performs a bitwise OR operation on `AL` with the hexadecimal value 30h.
- *Comment: `AX` = FF39h*
7. **popf**: Restores the flags register from the stack.
- *Comment: Restore the Carry flag*
This code snippet demonstrates basic ASCII arithmetic, binary-coded decimal (BCD) adjustment, and flag manipulation, which are foundational concepts in assembly language programming. Understanding these operations is crucial for controlling low-level machine behavior, especially in contexts requiring direct hardware interaction or performance optimizations.
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