MIPS统计二进制中1的个数代码故障排查求助

Let's break down the issues in your code that are causing unexpected behavior, then walk through a corrected version:

Key Problems in Your Original Code #

1. Infinite Loop When $t0 Becomes 0 #

Your loop doesn't check if $t0 is already 0 before entering the AND block. Once $t0 gets shifted right to 0, the code will keep running andi $t2, $t0, 1 (which returns 0), shift $t0 again (still 0), and jump back to AND forever. We need an early exit check for when $t0 hits 0.

2. Incorrect Value Loading for Output #

In the display section, la $a0, ($t1) is wrong—la loads memory addresses, but $t1 holds the counter's numeric value. To print the actual count, you need to move the value directly into $a0 with move $a0, $t1.

3. Redundant & Overcomplicated Code #

• The line la $t0, n when reading input is unnecessary: syscall 5 stores the user's input in $v0, and you already copy it to $t0 with move $t0, $v0.
• Initializing the counter by loading from the .data section is overkill. You can just use li $t1, 0 to set it to 0 directly.

Corrected Code #

# Count number of 1s in a 32 Bit Number
# $t0 = user input
# $t1 = counter
.data
prompt: .asciiz "Enter Number: "
result: .asciiz "Number of 1s counted: "

.text
# Prompt User for Number
li $v0, 4          
la $a0, prompt     
syscall            

# Get user Input
li $v0, 5          
syscall            
move $t0, $v0      # Move input value from $v0 to $t0

# Initialize counter to 0
li $t1, 0          

AND_LOOP:
beqz $t0, display  # Exit loop immediately if $t0 is 0
andi $t2, $t0, 1   # Check least significant bit
beq $t2, 1, increment_counter

# If LSB is 0, just shift right and continue
srl $t0, $t0, 1
b AND_LOOP

increment_counter:
add $t1, $t1, 1    # Increment counter
srl $t0, $t0, 1    # Shift right
b AND_LOOP

display:
# Print result message
li $v0, 4          
la $a0, result     
syscall            

# Print the counter value
move $a0, $t1      
li $v0, 1          
syscall            

# Exit program cleanly (good practice)
li $v0, 10         
syscall

Key Changes Explained #

• Added beqz $t0, display at the start of AND_LOOP to exit as soon as $t0 becomes 0, eliminating the infinite loop.
• Renamed labels for clarity (AND → AND_LOOP, loop → increment_counter) to make the logic easier to follow.
• Replaced the counter initialization with li $t1, 0 for simplicity and efficiency.
• Fixed the output step with move $a0, $t1 to pass the counter value correctly to the print syscall.
• Added an explicit exit syscall (li $v0,10) to properly terminate the program instead of letting it run off the end of the code.

内容的提问来源于stack exchange，提问作者Ooka