cc Aldy Hernandez <aldyh@redhat.com> and Andrew MacLeod <amacleod@redhat.com>,
they are author of new VRP analysis for GCC, just to make sure I didn't
mis-understanding or mis-interpreting anything on GCC site.
GCC 11 have better value range analysis, that give GCC more confidence
to perform more aggressive optimization, but it cause scalbn/scalbnf get
wrong result.
Using scalbn to demostrate what happened on GCC 11, see comments with VRP
prefix:
```c
double scalbn (double x, int n)
{
/* VRP RESULT: n = [-INF, +INF] */
__int32_t k,hx,lx;
...
k = (hx&0x7ff00000)>>20;
/* VRP RESULT: k = [0, 2047] */
if (k==0) {
/* VRP RESULT: k = 0 */
...
k = ((hx&0x7ff00000)>>20) - 54;
if (n< -50000) return tiny*x; /*underflow*/
/* VRP RESULT: k = -54 */
}
/* VRP RESULT: k = [-54, 2047] */
if (k==0x7ff) return x+x; /* NaN or Inf */
/* VRP RESULT: k = [-54, 2046] */
k = k+n;
if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */
/* VRP RESULT: k = [-INF, 2046] */
/* VRP RESULT: n = [-INF, 2100],
because k + n <= 0x7fe is false, so:
1. -INF < [-54, 2046] + n <= 0x7fe(2046) < INF
2. -INF < [-54, 2046] + n <= 2046 < INF
3. -INF < n <= 2046 - [-54, 2046] < INF
4. -INF < n <= [0, 2100] < INF
5. n = [-INF, 2100] */
if (k > 0) /* normal result */
{SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
if (k <= -54) {
/* VRP OPT: Evaluate n > 50000 as true...*/
if (n > 50000) /* in case integer overflow in n+k */
return huge*copysign(huge,x); /*overflow*/
else return tiny*copysign(tiny,x); /*underflow*/
}
k += 54; /* subnormal result */
SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
return x*twom54;
}
```
However give the input n = INT32_MAX, k = k+n will overflow, and then we
expect got `huge*copysign(huge,x)`, but new VRP optimization think
`n > 50000` is never be true, so optimize that into `tiny*copysign(tiny,x)`.
so the solution here is to moving the overflow handle logic before `k = k + n`.
- compiler is sometimes optimizing out the rounding check in
e_sqrt.c and ef_sqrt.c which uses two constants to create
an inexact operation
- there is a similar constant operation in s_tanh.c/sf_tanh.c
- make the one and tiny constants volatile to stop this
Use the more official fesetenv(FE_DFL_ENV) from _dll_crt0, thus
allowing to drop the _feinitialise declaration from fenv.h.
Provide a no-op _feinitialise in Cygwin as exportable symbol for really
old applications when _feinitialise was called from mainCRTStartup in
crt0.o.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
Drop the Cygwin-specific fenv.cc and fenv.h file and use the equivalent
newlib functionality now, so we have at least one example of a user for
this new mechanism.
fenv.c: allow _feinitialise to be called from Cygwin startup code
fenv.h: add declarations for fegetprec and fesetprec for Cygwin only.
Fix a comment.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
So far the build mechanism in newlib only allowed to either define
machine-specific headers, or headers shared between all machines.
In some cases, architectures are sufficiently alike to share header
files between them, but not with other architectures. A good example
is ix86 vs. x86_64, which share certain traits with each other, but
not with other architectures.
Introduce a new configure variable called "shared_machine_dir". This
dir can then be used for headers shared between architectures.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This Patch removes Soft Float code from MIPS.
Instead It adds the soft float code from RISCV
The code came from FreeBSD and assumes the FreeBSD softfp
implementation not the one with GCC. That was an overlooked and
fixed in the other fenv code already.
Signed-off-by: Eshan Dhawan <eshandhawan51@gmail.com>
This patch fixes the error found by Paul Zimmermann (see
https://homepages.loria.fr/PZimmermann/papers/#accuracy) regarding x
close to 1 and rather large y (specifically he found the case
powf(0x1.ffffeep-1,-0x1.000002p+27) which returns +Inf instead of the
correct value). We found 2 more values for x which show the same faulty
behaviour, and all 3 are fixed with this patch. We have tested all
combinations for x in [+1.fffdfp-1, +1.00020p+0] and y in
[-1.000007p+27, -1.000002p+27] and [1.000002p+27,1.000007p+27].
The current gamma, gamma_r, gammaf and gammaf_r functions return
|gamma(x)| instead of ln(|gamma(x)|) due to a change made back in 2002
to the __ieee754_gamma_r implementation. This patch fixes that, making
all of these functions map too their lgamma equivalents.
To fix the underlying bug, the __ieee754_gamma functions have been
changed to return gamma(x), removing the _r variants as those are no
longer necessary. Their names have been changed to __ieee754_tgamma to
avoid potential confusion from users.
Now that the __ieee754_tgamma functions return the correctly signed
value, the tgamma functions have been modified to use them.
libm.a now exposes the following gamma functions:
ln(|gamma(x)|):
__ieee754_lgamma_r
__ieee754_lgammaf_r
lgamma
lgamma_r
gamma
gamma_r
lgammaf
lgammaf_r
gammaf
gammaf_r
lgammal (on machines where long double is double)
gamma(x):
__ieee754_tgamma
__ieee754_tgammaf
tgamma
tgammaf
tgammal (on machines where long double is double)
Additional aliases for any of the above functions can be added if
necessary; in particular, I'm not sure if we need to include
__ieee754_gamma*_r functions (which would return ln(|(gamma(x)|).
Signed-off-by: Keith Packard <keithp@keithp.com>
----
v2:
Switch commit message to ASCII
For RISC-V targets without hardware FMA support, include the
common fma implementation to provide that API.
Signed-off-by: Keith Packard <keithp@keithp.com>
Like ARM, some RISC-V implementations have hardware sqrt. Support for
that can be detected at compile time, which the code did. However, the
filenames were incorrect so that both the risc-v specific and general
code were getting included in the resulting library.
Fix this by following the ARM model and #include'ing the general code
when the architecture-specific support is not available.
Signed-off-by: Keith Packard <keithp@keithp.com>
This is required to avoid colliding with files built from libm/common
that would end up with the same object name.
When libm.a was constructed from the individual sub-libraries, the
contents of the libm/common files would be replaced by that from
libm/machine/arm with the same name.
Signed-off-by: Keith Packard <keithp@keithp.com>
When HAVE_FAST_FMAF is set, use the vfma.f32 instruction, when
HAVE_FAST_FMA is set, use the vfma.f64 instruction.
Usually the compiler built-ins will already have inlined these
instructions, but provide these symbols for cases where that doesn't
work instead of falling back to the (inaccurate) common code versions.
Signed-off-by: Keith Packard <keithp@keithp.com>
Anything with fast FMA is assumed to have fast FMAF, along with
32-bit arms that advertise 32-bit FP support and __ARM_FEATURE_FMA
Signed-off-by: Keith Packard <keithp@keithp.com>
32-bit ARM processors with HW float (but not HW double) may define
__ARM_FEATURE_FMA, but that only means they have fast FMA for 32-bit
floats.
Signed-off-by: Keith Packard <keithp@keithp.com>
It was calling __math_uflow(0) instead of __math_uflowf(0), which
resulted in no exception being set on machines with exception support
for float but not double.
Signed-off-by: Keith Packard <keithp@keithp.com>
This removes the run-time configuration of errno support present in
portions of the math library and unifies all of the compile-time errno
configuration under a single parameter so that the whole library
is consistent.
The run-time support provided by _LIB_VERSION is no longer present in
the public API, although it is still used internally to disable errno
setting in some functions. Now that it is a constant, the compiler should
remove that code when errno is not supported.
This removes s_lib_ver.c as _LIB_VERSION is no longer variable.
Signed-off-by: Keith Packard <keithp@keithp.com>
The __ieee754 functions already return the right value in exception
cases, so don't modify those. Setting the library to _POSIX_/_IEEE_
mode now only affects whether errno is modified.
Signed-off-by: Keith Packard <keithp@keithp.com>
The y0, y1 and yn functions need separate conditions when x is zero as
that returns ERANGE instead of EDOM.
Also stop adjusting the return value from the __ieee754_y* functions
as that is already correct and we were just breaking it.
Signed-off-by: Keith Packard <keithp@keithp.com>
_IEEE_LIBM is the configuration value which controls whether the
original libm functions modify errno. Use that in the new math code as
well so that the resulting library is internally consistent.
Signed-off-by: Keith Packard <keithp@keithp.com>
C compilers may fold const values at compile time, so expressions
which try to elicit underflow/overflow by performing simple
arithemetic on suitable values will not generate the required
exceptions.
Work around this by replacing code which does these arithmetic
operations with calls to the existing __math_xflow functions that are
designed to do this correctly.
Signed-off-by: Keith Packard <keithp@keithp.com>
----
v2:
libm/math: Pass sign to __math_xflow instead of muliplying result
ld: libm.a(lib_a-fesetenv.o): in function `fesetenv':
newlib/libm/machine/arm/fesetenv.c:38: undefined reference to `vmsr_fpscr'
Signed-off-by: Sebastian Huber <sebastian.huber@embedded-brains.de>
Use the already existing stub files if possible. These files are
necessary to override the stub implementation with the machine-specific
implementation through the build system.
Reviewed-by: Sebastian Huber <sebastian.huber@embedded-brains.de>
Signed-off-by: Eshan dhawan <eshandhawan51@gmail.com>
The previous fenv support for ARM used the soft-float implementation of
FreeBSD. Newlib uses the one from libgcc by default. They are not
compatible. Having an GCC incompatible soft-float fenv support in
Newlib makes no sense. A long-term solution could be to provide a
libgcc compatible soft-float support. This likely requires changes in
the GCC configuration. For now, provide a stub implementation for
soft-float multilibs similar to RISC-V.
Move implementation to one file and delete now unused files. Hide
implementation details. Remove function parameter names from header
file to avoid name conflicts.
Provide VFP support if __SOFTFP__ is not defined like glibc.
Reviewed-by: Sebastian Huber <sebastian.huber@embedded-brains.de>
Signed-off-by: Eshan dhawan <eshandhawan51@gmail.com>
The IEEE spec for pow only has special case for x**0 and 1**y when x/y
are quiet NaN. For signaling NaN, the general case applies and these functions
should signal the invalid exception and return a quiet NaN.
Signed-off-by: Keith Packard <keithp@keithp.com>
Kito Cheng
Jeff Johnston
Ties Stuij
David Macek
Corinna Vinschen
Eshan dhawan
Paul Zimmermann
Fabian Schriever
Keith Packard
Keith Packard via Newlib
Sebastian Huber