Horton

Re: 64-bit integer subtraction bug on some platforms

Tom Lane <tgl@sss.pgh.pa.us>

View thread View on postgr.es
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: Dean Rasheed <dean.a.rasheed@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2023-11-08T16:08:05Z
Lists: pgsql-hackers 
Laurenz Albe <laurenz.albe@cybertec.at> writes:
> On Wed, 2023-11-08 at 11:58 +0000, Dean Rasheed wrote:
>> This should overflow, since the correct result (+9223372036854775808)
>> is out of range. However, on platforms without integer overflow
>> builtins or 128-bit integers, pg_sub_s64_overflow() does the
>> following:
>> ...
>> which fails to spot the fact that overflow is also possible when a ==
>> 0. So on such platforms, it returns the wrong result.
>> 
>> Patch attached.

> The patch looks good to me.

+1: good catch, fix looks correct.

			regards, tom lane

Commits

  1. Fix corner-case 64-bit integer subtraction bug on some platforms.