Opossum vs. float4 NaN
I see that opossum's owner just resurrected it after a period of being
MIA ... and it's failing a few regression tests with symptoms like
this:
SELECT 'NaN'::float4;
- float4
---------
- NaN
+ float4
+----------
+ Infinity
(1 row)I have no doubt that this is caused by the same platform bug that
I worked around in commit cb3e9e40b:
However, it emerges that this tickles a compiler or hardware bug on
buildfarm member opossum. Test results from commit 55e0e4581 show
conclusively that widening a float4 NaN to float8 produces Inf, not NaN,
on that machine; which accounts perfectly for the window RANGE test
failures it's been showing. We can dodge this problem by making
in_range_float4_float8 be an independent function, so that it checks
for NaN inputs before widening them.
The reason that it's reappeared is the refactoring we've done recently
around snprintf: float4out is now taking its float4 argument and widening
it to double to pass to strtod, which is where the checks for Inf/NaN
happen.
We could imagine band-aiding around this by adding something like
#if defined(__netbsd) && defined(__mips)
if (isnan(num))
// return "NaN"
#endif
to float4out, but ick. I was willing to do cb3e9e40b because it didn't
really make the code any uglier, but this would. And I bet the issue
is going to cause problems somewhere for Andrew's Ryu patch, too.
I'm thinking we should regretfully retire opossum, unless there's
a software update available for it that fixes this bug.
regards, tom lane
"Tom" == Tom Lane <tgl@sss.pgh.pa.us> writes:
Tom> The reason that it's reappeared is the refactoring we've done
Tom> recently around snprintf: float4out is now taking its float4
Tom> argument and widening it to double to pass to strtod, which is
Tom> where the checks for Inf/NaN happen.
[...]
Tom> to float4out, but ick. I was willing to do cb3e9e40b because it
Tom> didn't really make the code any uglier, but this would. And I bet
Tom> the issue is going to cause problems somewhere for Andrew's Ryu
Tom> patch, too.
Actually I'd expect the reverse - Ryu never widens a float4 to float8,
it does everything in integers after extracting the bits from the value;
so it should be immune to this issue.
--
Andrew (irc:RhodiumToad)
On Saturday, 26 January 2019, 16:00:24 GMT, Tom Lane <tgl@sss.pgh.pa.us> wrote: >>
I'm thinking we should regretfully retire opossum, unless there's
a software update available for it that fixes this bug.
I'm happy to update opossum to see if the issue goes away; likewise I'm just as happy to retire it completely. It'll still come online occasionally regardless, so makes no difference.
I guess the main question is; does anybody care about builds on a 20 year old netbsd/mipsel dinosaur? I noticed there are now mips64el and mips64eb build-farm members.
Glyn Astill <glynastill@yahoo.co.uk> writes:
I guess the main question is; does anybody care about builds on a 20 year old netbsd/mipsel dinosaur? I noticed there are now mips64el and mips64eb build-farm members.
I tend to think that variety in the buildfarm is intrinsically a good
thing. I'd rather see you continue to run the thing, perhaps with a
newer netbsd version if that will resolve the problem.
regards, tom lane