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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Dean Rasheed <dean.a.rasheed@gmail.com>
Cc: Yugo NAGATA <nagata@sraoss.co.jp>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Cc: Dave Page <dpage@pgadmin.org>
Subject: Re: Numeric x^y for negative x
Date: Fri, 06 Aug 2021 12:15:18 -0400
Message-ID: <2492411.1628266518@sss.pgh.pa.us> (raw)
In-Reply-To: <CAEZATCXZvcsuD3Nrm3F33YYavvKzMwRnjNw=3Of=Ra95oR6a4Q@mail.gmail.com>
References: <CAEZATCW6Dvq7+3wN3tt5jLj-FyOcUgT5xNoOqce5=6Su0bCR0w@mail.gmail.com>
	<CAEZATCUoVETahg892Qu3umjXX-V8J-F2xqQqunxckd5Se8KLyg@mail.gmail.com>
	<CAEZATCWAiXp7ocU3AMV6Pyvgv3O8x4-UBY+d=w+pziXXegdyOA@mail.gmail.com>
	<20210720181509.51a037ed0a8cb0f6d3ffda3a@sraoss.co.jp>
	<CAEZATCXGk5QQPRNjeXrd7EAkzhwwjgjLhEOp=zZwktX=zYradQ@mail.gmail.com>
	<20210722141136.573c11dfc06f4dd46b661bca@sraoss.co.jp>
	<CAEZATCW+yCy_11f56oDUecQzSrdO18gwPmOVwgbw6L0_HYJJeg@mail.gmail.com>
	<CAEZATCUWUV_BP41Ob7QY12oF+qDxjTWfDpkdkcOOuojrDvOLxw@mail.gmail.com>
	<2394813.1628179479@sss.pgh.pa.us>
	<CAEZATCX-giGez-yYFUbBAkKhUOOG+rAQuTbnXkemJma8gouWSQ@mail.gmail.com>
	<2449471.1628218684@sss.pgh.pa.us>
	<CAEZATCXZvcsuD3Nrm3F33YYavvKzMwRnjNw=3Of=Ra95oR6a4Q@mail.gmail.com>

Dean Rasheed <dean.a.rasheed@gmail.com> writes:
> So the "test for overflow by reverse-conversion" obviously isn't
> working as intended, and it's going through power_var_int() when it
> shouldn't. I don't think there's anything wrong with that code, so I
> think this is a compiler bug.

Yeah, looks like one.

> I guess the best thing to do is just test the value against
> PG_INT32_MIN/MAX, which is what int84() does. There are 2 other places
> in numeric.c that use similar code to check for int16/32 overflow, so
> it's possible that they're broken in the same way on that platform,
> but they aren't covered by the regression tests, so it's also possible
> that they're OK. Anyway, something like the attached seems likely to
> be safer.

Looks plausible by eyeball (I've not tested).

			regards, tom lane





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