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Consider this buggy UTF-8 validation snippet. Which line contains the subtle bug that allows invalid UTF-8 sequences to pass?

medium🐞 Bug Identification Q7 of Q15
Bit Manipulation - UTF-8 Validation
Consider this buggy UTF-8 validation snippet. Which line contains the subtle bug that allows invalid UTF-8 sequences to pass?
ANot checking if input bytes are 8-bit masked
BIncorrect bit shift in leading byte detection
CReturning False too early on valid bytes
DMissing decrement of remaining in continuation byte check
Step-by-Step Solution
Solution:

  1. Step 1: Identify continuation byte handling

    Continuation bytes must decrement remaining to track progress.

  2. Step 2: Locate missing decrement

    Code lacks 'remaining -= 1' after validating continuation byte, causing infinite remaining count.

  3. Final Answer:

    Option D -> Option D

  4. Quick Check:

    Missing decrement causes false positives [OK]
Quick Trick: Check if continuation byte counter decrements [OK]
Common Mistakes:
MISTAKES
  • Forgetting to decrement remaining
  • Misplacing decrement outside else block
Trap Explanation:
PITFALL
  • Candidates overlook decrement step, causing invalid sequences to pass validation.
Interviewer Note:
CONTEXT
  • Tests attention to subtle state updates in bitmask-based validation.
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