| From: | Isaac Morland <isaac(dot)morland(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
| Subject: | Re: Pointer subtraction with a null pointer |
| Date: | 2022-03-26 16:34:10 |
| Message-ID: | CAMsGm5ck5rfhE=MU+frgdEfUL8pHZBkkP=bBHXuHZzDXTcF_2w@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sat, 26 Mar 2022 at 12:24, Andres Freund <andres(at)anarazel(dot)de> wrote:
> NULL can never be part of the same "array object" or one past past the last
> element as the pointer it is subtracted from. Hence the undefined beaviour.
>
Even more fundamentally, NULL is not 0 in any ordinary mathematical sense,
even though it can be written 0 in source code and is often (but not
always) represented in memory as an all-0s bit pattern. I'm not at all
surprised to learn that arithmetic involving NULL is undefined.
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