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Message-ID: <20140404210207.GR26358@brightrain.aerifal.cx>
Date: Fri, 4 Apr 2014 17:02:07 -0400
From: Rich Felker <dalias@...ifal.cx>
To: musl@...ts.openwall.com
Subject: Re: printf issues
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
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