lib/msun: Cleanup after $FreeBSD$ removal

Remove no longer needed explicit inclusion of sys/cdefs.h.

PR: 276669
MFC after: 1 week

Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

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Use a builtin where possible in msun

Some of the functions in msun can be implemented using a compiler
builtin function to generate a small number of instructions. Implement
this support in fma, fma

Use a builtin where possible in msun

Some of the functions in msun can be implemented using a compiler
builtin function to generate a small number of instructions. Implement
this support in fma, fmax, fmin, and sqrt on arm64.

Care must be taken as the builtin can be implemented as a function
call on some architectures that lack direct support. In these cases
we need to use the original code path.

As we don't set errno on failure build with -fno-math-errno so the
toolchain doesn't convert a builtin into a function call when it
detects a failure, e.g. gcc will add a call to sqrt when the input
is negative leading to an infinite loop.

Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D32801

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lib: further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using mis-identified many licenses so this was mostly a manual - error
pr

lib: further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using mis-identified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

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IFC @230489 (pending review).

IFC @ r226824

Fix a double-rounding bug in fma{,f,l}. The bug would occur in
round-to-nearest mode when the result, rounded to twice machine
precision, was exactly halfway between two machine-precision
values. T

Fix a double-rounding bug in fma{,f,l}. The bug would occur in
round-to-nearest mode when the result, rounded to twice machine
precision, was exactly halfway between two machine-precision
values. The essence of the fix is to simulate a "sticky bit" in
the pathological cases, which is how hardware implementations
break the ties.

MFC after: 1 month

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Include math.h for the fmaf() prototype.

Add fma() and fmaf(), which implement a fused multiply-add operation.

Include math.h for the fmaf() prototype.

Add fma() and fmaf(), which implement a fused multiply-add operation.