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Message-ID: <20200223152147.GO1663@brightrain.aerifal.cx>
Date: Sun, 23 Feb 2020 10:21:47 -0500
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: Min and Max of 2 Floating Point numbers
On Sun, Feb 23, 2020 at 06:08:25PM +1100, Damian McGuckin wrote:
> The IEEE 754-2019 standard has changed the definition so as to
> properly propogate NaNs. The 1.2.0 version I just downloaded still
> follows the
> 2008 definition.
>
> ARM is smart enough to have 2 instructions, one (FMAX) which did
> propogate NaNs and one (FMAXNM) which follows the 2008 standard.
> That said, I do not personally compile on an ARM so I have no idea
> how you ask for FMAX or how you ask for FMAXNM?
>
> The PowerPC ISA 3.0 instruction properly propogates NaNs so it
> agrees with the new standard.
>
> The Intel instruction follows neither standard as far as I can tell. An
> interesting condition.
>
> Please tell me if I am wrong.
I'm not particularly aware of what the insns do. However..
> MUSL relevance: I believe that even in 1.2.0, MUSL's own fmax/fmin libc
> routines violate the IEEE 754-2019 standard which came out recently.
> Well, it was approved June, published July, released November. I
> think that is recent.
Unless by "propagate nans" you mean some specific behavior beyond
preserving one of the input nans, I don't see how we're violating it.
The < operator is only used if there are no nans and the signs are the
same.
Rich
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