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Date: Wed, 26 Jun 2024 08:55:08 +1000 (AEST)
From: Damian McGuckin <damianm@....com.au>
To: musl@...ts.openwall.com
Subject: Re: roundf() (and round(), and ...)

On Tue, 25 Jun 2024, Markus Wichmann wrote:

> If GCC is working according to the documentation, then not inside of 
> musl at the moment. These inlinings happen when a builtin instrinsic is 
> lowered into an assembler instruction, and by default, fabs* is 
> recognized as a builtin. But not when building musl, because musl builds 
> with -ffreestanding, which includes -fno-builtin.

As a general rule, I think that is a very wise decison.

> Rich has stated he wants to work around that with an
> implementation-internal header file that defines macros such as

> #define fabs(x) __builtin_fabs(x)

With IEEE 754 (in 5.5.1) defining all of copy, negate, abs (and copysign) 
as sign-bit operations, i.e. they are not just recommended operatons, I 
think this is a smart move, at least for the absolute value and sign copy
functionality.

- Damian

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