mailing list of musl libc
 help / color / mirror / code / Atom feed
* [musl] Min and Max of 2 Floating Point numbers
@ 2020-02-23  7:08 Damian McGuckin
  2020-02-23 15:21 ` Rich Felker
  2020-02-23 21:18 ` Florian Weimer
  0 siblings, 2 replies; 5+ messages in thread
From: Damian McGuckin @ 2020-02-23  7:08 UTC (permalink / raw)
  To: musl


Curiosity only (i.e. not a MUSL question). But it is somewhat relevant to 
MUSL which I note at the end of this email.

Besides the latest Intels, PowerPC, ARMs, I am just curious which of the 
CPU architectures implement this function directly at the assembler level, 
i.e. and hence avoiding a branch, i.e.

 	double f ....
 	double g ....
and
 	double fgmax = f > g ? f : g;

The word 'implement' is a bit loose. I am not talking about the definition 
in Annex F of the C standard.

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.

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.

Regards - Damian

Pacific Engineering Systems International, 277-279 Broadway, Glebe NSW 2037
Ph:+61-2-8571-0847 .. Fx:+61-2-9692-9623 | unsolicited email not wanted here
Views & opinions here are mine and not those of any past or present employer

^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2020-02-23 23:20 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-02-23  7:08 [musl] Min and Max of 2 Floating Point numbers Damian McGuckin
2020-02-23 15:21 ` Rich Felker
2020-02-23 21:03   ` Damian McGuckin
2020-02-23 21:18 ` Florian Weimer
2020-02-23 23:20   ` Damian McGuckin

Code repositories for project(s) associated with this public inbox

	https://git.vuxu.org/mirror/musl/

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).