[Solved] Consider the following buggy UTF-8 validation code snippet. Which line contains the subtle bug... Which line contains the subtle bug that can cause invalid UTF-8 sequences to be accepted as valid? | Bit Manipulation

Bit Manipulation - UTF-8 Validation

Consider the following buggy UTF-8 validation code snippet. Which line contains the subtle bug that can cause invalid UTF-8 sequences to be accepted as valid?

def validUtf8(data):
    remaining = 0
    for byte in data:
        if remaining == 0:
            if (byte >> 5) == 0b110:
                remaining = 1
            elif (byte >> 4) == 0b1110:
                remaining = 2
            elif (byte >> 3) == 0b11110:
                remaining = 3
            elif (byte >> 7) == 0:
                remaining = 0
            else:
                return False
        else:
            # Bug: missing check for continuation byte pattern
            remaining -= 1
    return remaining == 0

ALine with 'if remaining == 0:' condition

BLine with 'remaining -= 1' inside else block

CLine with 'if (byte >> 5) == 0b110:' condition

DLine with 'return remaining == 0' at the end

Step-by-Step Solution

Step 1: Identify where continuation bytes are checked
The else block handles continuation bytes, which must start with bits '10' (binary 0b10).
Step 2: Locate missing validation
The code decrements remaining without checking if the byte starts with '10', allowing invalid bytes to pass.
Final Answer:
Option B -> Option B
Quick Check:
Missing continuation byte pattern check causes acceptance of invalid sequences [OK]

Quick Trick: Check continuation bytes start with '10' before decrementing [OK]

Common Mistakes:

MISTAKES

Forgetting continuation byte pattern check
Miscounting remaining bytes

Trap Explanation:

PITFALL

Code looks correct but missing the critical check for continuation byte pattern leads to subtle bugs.

Interviewer Note:

CONTEXT

Tests candidate's ability to spot subtle bugs that pass many test cases but fail edge cases.

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More Bit Manipulation Quizzes

Consider the following buggy UTF-8 validation code snippet. Which line contains the subtle bug that can cause invalid UTF-8 sequences to be accepted as valid?

Step 1: Identify where continuation bytes are checked

Step 2: Locate missing validation

Final Answer:

Quick Check:

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