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fix: off-by-one error in binary_count_trailing_zeros for zero input (#14479) #14480

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fix: off-by-one error in binary_count_trailing_zeros for zero input (#14479) #14480

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refactor: off-by-one error in binary_count_trailing_zeros for zero input 
"The function returns `0` for `a == 0`, but mathematically, trailing zeros in binary representation of 0 are undefined (or conventionally treated as infinite). While `log2(a & -a)` fails for `a=0`, the current fallback to `0` is inconsistent with the documented behavior: `binary_count_trailing_zeros(16)` returns `4`, but `0` has infinitely many trailing zeros — returning `0` is misleading and could cause bugs in algorithms relying on this (e.g., bit manipulation loops expecting correct trailing zero counts)."

Signed-off-by: Zendy <50132805+zendy199x@users.noreply.github.com>
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zendy199x committed Mar 29, 2026
commit fcf063bf7645b6d6cf37270cea37b80dcf3aa294
8 changes: 5 additions & 3 deletions bit_manipulation/binary_count_trailing_zeros.py
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Expand Up @@ -17,7 +17,9 @@ def binary_count_trailing_zeros(a: int) -> int:
>>> binary_count_trailing_zeros(4294967296)
32
>>> binary_count_trailing_zeros(0)
0
Traceback (most recent call last):
...
ValueError: Input value must be a positive integer
>>> binary_count_trailing_zeros(-10)
Traceback (most recent call last):
...
Expand All @@ -31,11 +33,11 @@ def binary_count_trailing_zeros(a: int) -> int:
...
TypeError: '<' not supported between instances of 'str' and 'int'
"""
if a < 0:
if a <= 0:
raise ValueError("Input value must be a positive integer")
elif isinstance(a, float):
raise TypeError("Input value must be a 'int' type")
return 0 if (a == 0) else int(log2(a & -a))
return int(log2(a & -a))


if __name__ == "__main__":
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