Question
Answer and Explanation
Reading multiple integers in MIPS assembly involves using syscalls and a loop to repeatedly read input and store it. Here's how you can accomplish this:
1. Utilize the `syscall` instruction: The `syscall` instruction is how you interface with the operating system. To read an integer, you use `syscall` code 5. To print, you'd use code 1, etc.
2. Load the appropriate code into `$v0`: Before issuing the `syscall`, you must load the syscall code into register `$v0`. For reading an integer, you load the value 5 into `$v0`.
3. The Read Integer operation stores the read integer in `$v0`: After the `syscall`, the integer that the user input is stored in `$v0` so you can operate with that value.
4. Use a loop: To read multiple integers, you'll need to use a loop. This typically involves:
a. Setting up a counter for the number of integers to read, stored in a register, for example `$t0`.
b. Using a label to mark the beginning of the loop.
c. Performing the read operation inside the loop.
d. Incrementing your array index to store the next integer in a next position.
e. Decrementing the counter.
f. Branching back to the beginning of the loop if the counter is not zero.
5. Store the integers in an array or a specific memory location: After you read each integer, you'll want to store it. This will likely involve using the `sw` (store word) instruction.
6. Example MIPS Code:
Here's a sample MIPS code snippet that reads 5 integers from the user and stores them in memory:
.data
array: .space 20 # Space for 5 integers (4 bytes each)
count: .word 5 # Number of integers to read
.text
.globl main
main:
la $t1, array # Load the address of the array
lw $t0, count # Load the count of integers
li $t2, 0 # Initialize array index
read_loop:
beq $t0, $zero, end_read_loop # If count is 0, exit loop
li $v0, 5 # Syscall code for read integer
syscall # Read an integer from input
sw $v0, ($t1) # Store the integer in the array
addi $t1, $t1, 4 # Increment the array address
addi $t2, $t2, 1 # Increment array index
addi $t0, $t0, -1 # Decrement the counter
j read_loop # Go back to the loop's start
end_read_loop:
li $v0, 10 # Syscall code for exit
syscall # Exit program
Explanation:
- The `.data` section reserves space for an array (`array`) to hold the integers and stores the number of integers to read into the variable `count`.
- The `.text` section contains the program code, beginning with the `main` label.
- The `read_loop` label marks the beginning of the loop. The loop continues until the counter (`$t0`) is equal to zero.
- Inside the loop, syscall code 5 is used to read an integer from the user, and it’s stored in `$v0`.
- The integer from `$v0` is then stored into the memory pointed to by register `$t1` which initially has the base address of our array, it gets incremented by 4 on each pass.
- The loop counter (`$t0`) is decremented, and the program jumps back to `read_loop`.
- Finally, the program exits using syscall code 10.
This MIPS code provides a straightforward example of how to read multiple integers from the user. You can adjust the number of integers to read by changing the value stored in the variable `count`. Also you may need to adjust the logic to fit more specific requirements.