Re: [PATCH 0/3] MR9926: ntdll: Make RtlEncodePointer / RtlDecodePointer compatible.

[Alfred Agrell (＠Alcaro)]

Alfred Agrell (@Alcaro) commented about dlls/ntdll/tests/rtl.c:
> free( group_sid );
>  }
>
> +static ULONG_PTR rotate_bits_right( ULONG_PTR v, ULONG count )
> +{
> +    static const unsigned int bits = sizeof(v) * 8;
> +
> +    count %= bits;
> +    return (v >> count) | (v << (bits - count));

If count==0, bits-count = 64, and v<<64 is UB. (Or 32 on 32bit builds, but still UB.)

Consider instead `return (v >> (count % bits)) | (v << ((bits - count) % bits));`. https://godbolt.org/z/9nWP6zK8P (Or stdc_rotate_right, except that one doesn't exist until C23.)

Same for the rotate left function below, and the actual encode/decode pointer functions.

-- 
https://gitlab.winehq.org/wine/wine/-/merge_requests/9926#note_127365