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Date: Mon, 29 Jun 2020 18:26:42 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: "mayuresh@...he.in" <mayuresh@...he.in>
Cc: musl@...ts.openwall.com
Subject: Re: Posits support under Musl libc?

* mayuresh@...he.in <mayuresh@...he.in> [2020-06-29 14:56:09 +0200]:
> On Monday, June 29, 2020 05:34 PM IST, Pascal Cuoq <cuoq@...st-in-soft.com> wrote:
> 
> > > Can the "musl" libc project consider supporting the Posit number format in the math routines?
> >
> > > More details;
> > > https://posithub.org/docs/Posits4.pdf
> > > https://posithub.org/docs/BeatingFloatingPoint.pdf
> >
> > > And a sample implementation;
> > > https://gitlab.com/cerlane/SoftPosit
> >
> > I am not a musl contributor and have no say in what it should contain or not, but why in hell a software implementation of a non-standard floating-point format that only its inventor seems to think has any concrete advantage over IEEE 754 belong in a libc the goals of which are below?
> >
> > “lightweight, fast, simple, free, and strives to be correct in the sense of standards-conformance and safety.” (from https://musl.libc.org/ )
> >
> > Posits are 1 out of 5 (I think they are free).
> 
> Posits are lightweight, fast, free and produce the same results across platforms, something which IEEE 754 doesn't guarantee. To top that, IEEE 754 isn't even a standard but just a set of guidelines which are usually implemented incorrectly due to misinterpretation or lack of expertise. So in that sense, Posits are safer than Floating-point.
> 
> That makes Posits, 4 out of 5 (which seems a much better proposition).

i would not hold my breath for posit support even if it was the
best possible floating-point format.

it has to be properly standardized and added to hw architectures.

then the related software standards need to be developed (abi,
programming language support, math library behaviour for special
cases, printf format specifiers, etc)

then the tooling support has to be added (compilers, emulators,
softfloat libraries, etc)

then we can come back and consider doing something about it in
musl.

(and even then it will take time for it to be usable in user
code: requires widely deployed hw, protocol and file format
updates, new algorithm designs and review of existing algorithms
for compatibility)

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