From: Morten Welinder <mwelinder@gmail.com>
To: musl@lists.openwall.com
Subject: Re: printf issues
Date: Fri, 4 Apr 2014 22:08:47 -0400 [thread overview]
Message-ID: <CANv4PNnXDpO2g-_9XwDw1+nX2O9aq+7UodTUa5yzEn0bsas89g@mail.gmail.com> (raw)
In-Reply-To: <20140404210207.GR26358@brightrain.aerifal.cx>
> [...] excess precision (FLT_EVAL_METHOD==2). This is why
> musl uses long double internally everywhere that rounding semantics
> matter.
That's what I thought, but it's not actually what I see over in src/math/.
If I look in src/math/floor.c I see an explicit cast from double to double
used to get rid of excess precision. The similar thing ought to work in
fmt_fp.
Morten
On Fri, Apr 4, 2014 at 5:02 PM, Rich Felker <dalias@aerifal.cx> wrote:
> On Fri, Apr 04, 2014 at 04:01:08PM -0400, Morten Welinder wrote:
>> In fmt_fmt, the rounding decision is done using this test:
>>
>> /* Decide whether to round by probing round+small */
>> if (round+small != round) { ...
>>
>> Why is this done with long double?
>>
>> The reason I ask is that the Valgrind situation improves a lot if
>> this is done with doubles.
>>
>> (Valgrind situation: Valgrind emulates long doubles, poorly, by using
>> simple doubles. See, for example, https://bugs.kde.org/show_bug.cgi?id=164298)
>
> This is a known issue that needs to be fixed in valgrind. It's
> impossible to do anything useful with rounding on x86 with types other
> than double, due to excess precision (FLT_EVAL_METHOD==2). This is why
> musl uses long double internally everywhere that rounding semantics
> matter.
>
> Rich
next prev parent reply other threads:[~2014-04-05 2:08 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-04 13:32 Morten Welinder
2014-04-04 14:12 ` Rich Felker
2014-04-04 14:15 ` Szabolcs Nagy
2014-04-04 14:35 ` Morten Welinder
2014-04-04 14:56 ` Szabolcs Nagy
2014-04-04 15:07 ` Rich Felker
2014-04-04 17:42 ` Morten Welinder
2014-04-04 18:54 ` Szabolcs Nagy
2014-04-04 20:01 ` Morten Welinder
2014-04-04 20:22 ` Morten Welinder
2014-04-04 21:08 ` Rich Felker
2014-04-04 22:50 ` Morten Welinder
2014-04-05 0:01 ` Morten Welinder
2014-04-05 1:41 ` Rich Felker
2014-04-07 7:29 ` Rich Felker
2014-04-07 13:40 ` Morten Welinder
2014-04-07 14:13 ` Morten Welinder
2014-04-07 15:36 ` Szabolcs Nagy
2014-04-07 18:04 ` Rich Felker
2014-04-04 20:54 ` Szabolcs Nagy
2014-04-04 21:02 ` Rich Felker
2014-04-05 2:08 ` Morten Welinder [this message]
2014-04-05 2:50 ` Rich Felker
2014-04-06 23:07 ` Szabolcs Nagy
2014-04-04 21:00 ` Rich Felker
2014-04-04 21:10 ` Szabolcs Nagy
2014-04-04 20:58 ` Rich Felker
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