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Date: Sun, 23 Feb 2020 10:21:47 -0500
From: Rich Felker <>
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


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