Quoting Martin Storsjö (2024-09-24 10:53:38)
> While shifting "value" to left, we would iterate through all bits
> of an unsigned long long, while we only expect to count through
> "size * CHAR_BIT" bits.
>
> This fixes fate with MSVC.
> ---
> compat/stdbit/stdbit.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/compat/stdbit/stdbit.h b/compat/stdbit/stdbit.h
> index b434fc2357..3197a24938 100644
> --- a/compat/stdbit/stdbit.h
> +++ b/compat/stdbit/stdbit.h
> @@ -179,9 +179,10 @@ static inline unsigned int
> __stdc_trailing_zeros(unsigned long long value,
> unsigned int size)
> {
> unsigned int zeros = size * CHAR_BIT;
> + unsigned long long mask = (1ULL << (size * CHAR_BIT)) - 1;
This is UB for size == sizeof(unsigned long long).
>
> while (value != 0) {
> - value <<= 1;
> + value = (value << 1) & mask;
Otherwise looks ok.
--
Anton Khirnov
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