Horton

Re: Avoid undefined behavior with msvc compiler (src/include/port/pg_bitutils.h)

John Naylor <john.naylor@enterprisedb.com>

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From: John Naylor <john.naylor@enterprisedb.com>
To: Ranier Vilela <ranier.vf@gmail.com>
Cc: Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2023-07-30T08:07:25Z
Lists: pgsql-hackers 
On Sat, Jul 29, 2023 at 7:37 PM Ranier Vilela <ranier.vf@gmail.com> wrote:
>
> Hi,
>
> The pg_leftmost_one_pos32 function with msvc compiler,
> relies on Assert to guarantee the correct result.
>
> But msvc documentation [1] says clearly that
> undefined behavior can occur.

It seems that we should have "Assert(word != 0);" at the top, which matches
the other platforms anyway, so I'll add that.

> Fix by checking the result of the function to avoid
> a possible undefined behavior.

No other platform does this, and that is by design. I'm also not
particularly impressed by the unrelated cosmetic changes.

--
John Naylor
EDB: http://www.enterprisedb.com

Commits

  1. Bring some MSVC asserts in line with other platforms