Avoid raising unexpected floating point exceptions in libm

When using clang with x86_64 CPUs that support AVX, some floating point
transformations may raise exceptions that would not have been raised by
the original code. To avoid this, use the -fp-exception-behavior=maytrap
flag, introduced in clang 10.0.0.

In particular, this fixes a number of test failures with ctanhf(3) and
ctanf(3), when libm is compiled with -mavx. An unexpected FE_INVALID
exception is then raised, because clang emits vdivps instructions to
perform certain divides. (The vdivps instruction operates on multiple
single-precision float operands simultaneously, but the exceptions may
be influenced by unused parts of the XMM registers. In this particular
case, it was calculating 0 / 0, which results in FE_INVALID.)

If -fp-exception-behavior=maytrap is specified however, clang uses
vdivss instructions instead, which work on one operand, and should not
raise unexpected exceptions.

Reported by: olivier
Reviewed by: arichardson
PR: 254911
Differential Revision: https://reviews.freebsd.org/D29686

(cherry picked from commit 3b00222f156dca5700c839d73e36daf479fa640c)

Only use -fp-exception-behavior=maytrap on x86, for now

After 3b00222f156d, it turns out that clang only supports strict
floating point semantics for SystemZ and x86 at the moment, while for
other architectures it is still experimental.

Therefore, only use -fp-exception-behavior=maytrap on x86 for now,
otherwise this option results in "error: overriding currently
unsupported use of floating point exceptions on this target
[-Werror,-Wunsupported-floating-point-opt]" on other architectures.

Fixes: 3b00222f156d
PR: 254911

(cherry picked from commit bae9fd0b33462e9506c3ac3400089c6dbc4aee8f)

Git Hash: cabc474b2dc9c6741b240e454da86a7ff2ff9f9c
Git Author: dim@FreeBSD.org

libm: squelch -Woverflow from gcc6

Sponsored by: Dell EMC Isilon

(cherry picked from commit 50b06886a715d7be052e1742f7d11ce82928f134)

Git Hash: e7cc5cda88f079b80636aa7f71b0fc671701f77d
Git Author: vangyzen@FreeBSD.org

Avoid -pedantic warnings about using _Generic in __fp_type_select

When compiling parts of math.h with clang using a C standard before C11,
and using -pedantic, it will result in warnings similar to:

bug254714.c:5:11: warning: '_Generic' is a C11 extension [-Wc11-extensions]
return !isfinite(1.0);
^
/usr/include/math.h:111:21: note: expanded from macro 'isfinite'
^
/usr/include/math.h:82:39: note: expanded from macro '__fp_type_select'
^

This is because the block that enables use of _Generic is conditional
not only on C11, but also on whether the compiler advertises support for
C generic selections via __has_extension(c_generic_selections).

To work around the warning without having to pessimize the code, use the
__extension__ keyword, which is supported by both clang and gcc. While
here, remove the check for __clang__, as _Generic has been supported for
a long time by gcc too now.

Reported by: yuri
PR: 254714

Git Hash: b582d1422b4db6c22ff061a32257a83405d06cc9
Git Author: dim@FreeBSD.org

Build lib/msun tests with compiler builtins disabled

This forces the compiler to emit calls to libm functions, instead of
possibly substituting pre-calculated results at compile time, which
should help to actually test those functions.

Reviewed by: emaste, arichardson, ngie
Differential Revision: https://reviews.freebsd.org/D28577

(cherry picked from commit cf97d2a1dab8f2cddc4466fe64d37818339c73be)

riscv: Add a soft-float implementation of fabs()

We could just use a C implementation using __builtin_fabs(), but using
this assembly version guarantees that there is no additional prolog/epilog
code. Additionally, clang generates worse code for masking off the top bit
than GCC: https://bugs.llvm.org/show_bug.cgi?id=49377.

This fixes the RISCV64 softfloat world build after cf97d2a1dab8. That commit
added -fno-builtin to the msun tests which resulted in the first references to
fabs (previously the compiler inlined all calls).

Reviewed By: dim
Reported by: mjg
Differential Revision: https://reviews.freebsd.org/D28994

(cherry picked from commit 524b018d200408bed5eb0d2b892db5b9fb46808b)

riscv: Fix whitespace issues in fabs added in 524b018d2004

(cherry picked from commit 066dab17e7a4a78d43dbcef8119960ddc8090a73)

Git Hash: 7ee9798bad0b42983259e3a9e131789f4a49c117
Git Author: dim@FreeBSD.org

Fix incorrect hypotl(3) result with subnormal numbers

This adjusts the factor used to scale the subnormal numbers, so it
becomes the right value after adjusting its exponent. Thanks to Steve
Kargl for finding the most elegant fix.

Also enable the hypot tests, and add a test case for this bug.

PR: 253313

(cherry picked from commit d3338f3355a612cf385632291f46c5777bba8d18)

Fix lib/msun/test builds on platforms without 80-bit long doubles

After d3338f3355a612cf385632291f46c5777bba8d18, the lib/msun test case
'hypotl_near_underflow' would fail to compile on platforms where long
doubles weren't 80 bit, like on x86. Disable this particular test on
such platforms for now.

PR: 253313

(cherry picked from commit 25120662284466ecef976df8f86e97bafdedf991)

Git Hash: 6287b5978c5f3959ad7f9494681cf94d1243120e
Git Author: dim@FreeBSD.org

Fix incorrect powf(3) result with x near 1 and |y| much larger than 1

This adjusts the check to trigger overflow/underflow to a slightly lower
value.

Before: powf(9.999995e-01, -1.342177e+08) -> inf
After: powf(9.999995e-01, -1.342177e+08) -> 1.858724e+31

(cherry picked from commit 93fc67896550548f91b307dbe3053f11db5d4a8a)

Add test case for 93fc67896550 (incorrect powf(3) result)

This adds the test case to contrib/netbsd-tests/lib/libm/t_pow.c, as it
is currently the only place testing pow(3) and friends.

(cherry picked from commit 51af03328755c9095e94d20858a8d10acfe412ae)

Git Hash: 182881658138a3b074a78649acd4e768c204b44f
Git Author: sgk@troutmask.apl.washington.edu

test_inf_inputs: Use atf_tc_expect_fail() instead of atf_tc_skip()

Reviewed By: lwhsu
Differential Revision: https://reviews.freebsd.org/D28396

(cherry picked from commit 4d2edf3af1dbd8a3e7cf1b22343a1ecfc2dd41ba)

Fix lib/msun's ctrig_test/test_inf_inputs test case with clang >= 10

This sprinkles a few strategic volatiles in an attempt to defeat clang's
optimization interfering with the expected floating-point exception
flags.

Reported by: lwhsu
PR: 244732

(cherry picked from commit ac76bc1145dd7f4476e5d982ce8f355f71015713)

Git Hash: ca9df934a5520f9692eb6808b1d02c0d3f1b927a
Git Author: arichardson@FreeBSD.org

MFC r358887 (partially):

Temporarily skip 2 failing tests after llvm10 import

The DDifference of the original revision to -head is only
lib.msun.ctrig_test.test_inf_inputs skipped.

PR: 244732
Sponsored by: The FreeBSD Foundation

r355120 | dim | 2019-11-26 23:01:09 +0100 (Tue, 26 Nov 2019) | 32 lines

The fdlibm hypot() implementations shouldn't potentially left-shift
negative numbers (invoking undefined behavior)

Summary:
Various paths through hypot(x, y) will multiply x and y by a power of
two, perform the calculation in a range where IEEE-754 provides greater
precision, then undo the multiplication to determine the true result.
Undoing that multiplication is implemented as t1*w, where t1=2**k.

2**k is often computed by taking the high word of 1.0, then adding k<<20
(for doubles or long doubles) or k<<23 (for floats) to it, then
overwriting that high word. But when k is negative this left-shifts a
negative value -- and that's undefined behavior in many editions of C
and C++.

This patch should fix all hypot implementations to compute 2**k without
triggering this particular bit of undefined behavior.

Test Plan: I've only very lightly tested out the hypot(double, double)
change, in SpiderMonkey's JavaScript engine, for consistency with prior
behavior. The other functions' changes have more or less only been
eyeballed. Careful examination appreciated! Do note, however, that an
error in any of these changes would most likely produce a value that is
incorrect by a factor of two, so any mistake would most likely be
glaring if invoked.

Submitted by: Jeff Walden <jwalden@mit.edu>
Obtained from: https://github.com/freebsd/freebsd/pull/414
Reviewed by: dim, lwhsu
Differential Revision: https://reviews.freebsd.org/D22354

MFC r354520:

Get the fix in back by reverting the part accidentally included in r354491.

This brings back r354467.

Sponsored by: The FreeBSD Foundation

MFC r354255:

Add __isnan()/__isnanf() aliases for compatibility with glibc and CUDA

Even though clang comes with a number of internal CUDA wrapper headers,
compiling sample CUDA programs will result in errors similar to:

In file included from <built-in>:1:
In file included from /usr/lib/clang/9.0.0/include/__clang_cuda_runtime_wrapper.h:204:
/usr/home/arr/cuda/var/cuda-repo-10-0-local-10.0.130-410.48/usr/local/cuda-10.0//include/crt/math_functions.hpp:2910:7: error: no matching function for call to '__isnan'
if (__isnan(a)) {
^~~~~~~
/usr/lib/clang/9.0.0/include/__clang_cuda_device_functions.h:460:16: note: candidate function not viable: call to __device__ function from __host__ function
__DEVICE__ int __isnan(double __a) { return __nv_isnand(__a); }
^

CUDA expects __isnan() and __isnanf() declarations to be available,
which are glibc specific extensions, equivalent to the regular isnan()
and isnanf().

To provide these, define __isnan() and __isnanf() as aliases of the
already existing static inline functions __inline_isnan() and
__inline_isnanf() from math.h.

Reported by: arrowd
PR: 241550

MFC r353329:

msun: Silence new harmless -Wimplicit-int-float-conversion warnings

Clang from trunk recently added a warning for when implicit int-to-float
conversions cause a loss of precision. The code in question is designed
to be able to handle that, so add explicit casts to silence this.

Submitted by: James Clarke <jrtc27@jrtc27.com>
Reviewed by: dim
Obtained from: CheriBSD
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D21913

MFC r352710:

Do not left-shift a negative number (inducing undefined behavior in
C/C++) in exp(3), expf(3), expm1(3) and expm1f(3) during intermediate
computations that compute the IEEE-754 bit pattern for |2**k| for
integer |k|.

The implementations of exp(3), expf(3), expm1(3) and expm1f(3) need to
compute IEEE-754 bit patterns for 2**k in certain places. (k is an
integer and 2**k is exactly representable in IEEE-754.)

Currently they do things like 0x3FF0'0000+(k<<20), which is to say they
take the bit pattern representing 1 and then add directly to the
exponent field to get the desired power of two. This is fine when k is
non-negative.

But when k<0 (and certain classes of input trigger this), this
left-shifts a negative number -- an operation with undefined behavior in
C and C++.

The desired semantics can be achieved by instead adding the
possibly-negative k to the IEEE-754 exponent bias to get the desired
exponent field, _then_ shifting that into its proper overall position.

(Note that in case of s_expm1.c and s_expm1f.c, there are SET_HIGH_WORD
and SET_FLOAT_WORD uses further down in each of these files that perform
shift operations involving k, but by these points k's range has been
restricted to 2 < k <= 56, and the shift operations under those
circumstances can't do anything that would be UB.)

Submitted by: Jeff Walden, https://github.com/jswalden
Obtained from: https://github.com/freebsd/freebsd/pull/411
Obtained from: https://github.com/freebsd/freebsd/pull/412

MFC r348500:

Partially revert r271349, which disabled the msun cexp test #4 on i386.

Ensure the expected result is stored first in a volatile variable with
the desired type. This makes all the tests succeed.

Slightly changed from the original pull request, but functionally the
same.

Approved by: re (gjb)
Obtained from: https://github.com/freebsd/freebsd/pull/401
Submitted by: Moritz Buhl <gh@moritzbuhl.de>
PR: 191676

MFC r343953:
Replace calls to sin(x) and cos(x) with a single call to sincos().
Replace calls to sinf(x) and cosf(x) with a single call to sincosf().

Approved by: grog, jhb (mentors)

MFC r343023:
msun: reduce diff between src/e_j0.c and src/e_j0f.c

PR: 229501

MFC r327400 (by eadler):

cacos(3): correct spelling of 'I'

In some cases we had 'i' instead of 'I'.

PR: 195517
Submitted by: stephen

MFC r329259 (by eadler):

msun: signed overflow in atan2

As a component of atan2(y, x), the case of x == 1.0 is farmed out to
atan(y). The current implementation of this comparison is vulnerable
to signed integer underflow (that is, undefined behavior), and it's
performed in a somewhat more complicated way than it need be. Change
it to not be quite so cute, rather directly comparing the high/low
bits of x to the specific IEEE-754 bit pattern that encodes 1.0.

Note that while there are three different e_atan* files in the
relevant directory, only this one needs fixing. e_atan2f.c already
compares against the full bit pattern encoding 1.0f, while
e_atan2l.cuses bitwise-ands/ors/nots and so doesn't require a change.

Closes #130

Submitted by: Jeff Walden (@jswalden github PR #130)
Reviewed by: bde

MFC r334721 (by cem):

clog.3, complex.3: Fix typos and igor style issues

PR: 228783
Reported by: Karsten <freebsd-bugzilla AT kkoenig.net>

MFC r336299 (by mmacy):

msun: add ld80/ld128 powl, cpow, cpowf, cpowl from openbsd

This corresponds to the latest status (hasn't changed in 9+
years) from openbsd of ld80/ld128 powl, and source cpowf, cpow,
cpowl (the complex power functions for float complex, double
complex, and long double complex) which are required for C99
compliance and were missing from FreeBSD. Also required for
some numerical codes using complex numbered Hamiltonians.

Thanks to jhb for tracking down the issue with making
weak_reference compile on powerpc.

When asked to review, bde said "I don't like it" - but
provided no actionable feedback or superior implementations.

Discussed with: jhb
Submitted by: jmd
Differential Revision: https://reviews.freebsd.org/D15919

MFC r336563:

Recommit r336497: Fix powl, cpow, cpowf, and cpowl imports from OpenBSD

This is a follow-up to r336299.

* lib/msun/Makefile:
. Remove polevll.c

* lib/msun/ld80/e_powl.c:
. Copy contents of polevll.c to here. This is the only consumer of
these functions. Make functions 'static inline'.
. Make reducl a 'static inline' function.

* lib/msun/man/exp.3:
. Remove BUGS section that no longer applies.

* lib/msun/src/math_private.h:
. Remove prototypes of __p1evll() and __polevll()

* lib/msun/src/s_cpow.c:
* lib/msun/src/s_cpowf.c:
* lib/msun/src/s_cpowl.c
. Include math_private.h.
. Use the CMPLX macro from either C99 or math_private.h (depends on
compiler support) instead of the problematic use of complex I.

Submitted by: Steve Kargl <sgk@troutmask.apl.washington.edu>
PR: 229876

MFC r336090:
Reduce diff between msun/src/e_pow.c and msun/src/e_powf.c.

PR: 229420

MFC r336089:
Fix whitespace issues in bessel function routines.

PR: 229423

MFC r334445:

Resolve conflicts between macros in fenv.h and ieeefp.h

This is a follow-up to r321483, which disabled -Wmacro-redefined for
some lib/msun tests.

If an application included both fenv.h and ieeefp.h, several macros such
as __fldcw(), __fldenv() were defined in both headers, with slightly
different arguments, leading to conflicts.

Fix this by putting all the common macros in the machine-specific
versions of ieeefp.h. Where needed, update the arguments in places
where the macros are invoked.

This also slightly reduces the differences between the amd64 and i386
versions of ieeefp.h.

Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D15633

MFC r333577:
Add implementations for clog(3), clogf(3), and clogl(3).

PR: 216863

Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)