libm: fma: correct zero sign with small inputs

This is a fixed version of 888796ade284.

PR: 277783
Reported by: Victor Stinner
Reviewed by: emaste
MFC after: 1 week

libm: add parens to clarify expressions in fma, fmal

Obtained from: NetBSD

Revert "libm: fma: correct zero sign with small inputs"

This change introduced a test failure, so revert until that can be
addressed.

This reverts commit 888796ade2842486d3167067e8034254c38aadd3.

Revert "libm: fma: correct zero sign with small inputs"

This change introduced a test failure, so revert until that can be
addressed.

This reverts commit 888796ade2842486d3167067e8034254c38aadd3.

PR: 277783
Reported by: rlibby
Sponsored by: The FreeBSD Foundation

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msun: update Clang bug reference in fma test

LLVM bugzilla bug 8100 became issue #8472 with the migration to GitHub.

https://github.com/llvm/llvm-project/issues/8472

libm: fma: correct zero sign with small inputs

PR: 277783
Reported by: Victor Stinner
Submitted by: kargl
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D44433

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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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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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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Merge head r233826 through r256722.

Merge from head

IFC @ r254014

IFC @253398

IFC @ r252288

Make the order of operations for lib/msun more clear.

Tested with md5 sum of object code

Reported by: swildner@DragonFlyBSD.org
Submitted by: bde

Merge fresh head.

Fix some regressions caused by the switch from gcc to clang. The fixes
are workarounds for various symptoms of the problem described in clang
bugs 3929, 8100, 8241, 10409, and 12958.

The regression

Fix some regressions caused by the switch from gcc to clang. The fixes
are workarounds for various symptoms of the problem described in clang
bugs 3929, 8100, 8241, 10409, and 12958.

The regression tests did their job: they failed, someone brought it
up on the mailing lists, and then the issue got ignored for 6 months.
Oops. There may still be some regressions for functions we don't have
test coverage for yet.

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IFC @230489 (pending review).

IFC @ r226824

Fix a regression introduced in r226371: When the high part of x*y
exactly cancels with z, return the low part of x*y instead of
discarding it.

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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Refactor this code by introducing separate functions to handle the
extra-precision add and multiply operations. This simplifies future
work but shouldn't result in any functional change.

Fix some corner cases:
- fma(x, y, z) returns z, not NaN, if z is infinite, x and y are finite,
x*y overflows, and x*y and z have opposite signs.
- fma(x, y, z) doesn't generate an overflow, underf

Fix some corner cases:
- fma(x, y, z) returns z, not NaN, if z is infinite, x and y are finite,
x*y overflows, and x*y and z have opposite signs.
- fma(x, y, z) doesn't generate an overflow, underflow, or inexact exception
if z is NaN or infinite, as per IEEE 754R.
- If the rounding mode is set to FE_DOWNWARD, fma(1.0, 0.0, -0.0) is -0.0,
not +0.0.

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Fix the double rounding problem with subnormals, and
remove the XXX comments, which no longer apply.

Implement fmal.