8000 bpo-45548: Remove _math.c workarounds for pre-C99 libm by tiran · Pull Request #29179 · python/cpython · GitHub
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bpo-45548: Remove _math.c workarounds for pre-C99 libm #29179

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Merged
merged 4 commits into from
Oct 25, 2021
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bpo-45548: Remove _math.c workarounds for pre-C99 libm #29179

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ba5de5f
bpo-45548: Remove _math.c workarounds for pre-C99 libm
tiran Oct 22, 2021
0ea1734
Update Misc/NEWS.d/next/Build/2021-10-24-21-49-49.bpo-45548.UWx0UC.rst
tiran Oct 25, 2021
fc3db0c
Remove _math.c depends from setup.py
tiran Oct 25, 2021
45b7fa6
Update comments, it's _math.h now
tiran Oct 25, 2021
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bpo-45548: Remove _math.c workarounds for pre-C99 libm 
The :mod:`math` and :mod:`cmath` implementation now require a C99 compatible
``libm`` and no longer ship with workarounds for missing acosh, asinh,
expm1, and log1p functions.

The changeset also removes ``_math.c`` and moves the last remaining
workaround into ``_math.h``. This simplifies static builds with
``Modules/Setup`` and resolves symbol conflicts.

Co-authored-by: Mark Dickinson <mdickinson@enthought.com>
Co-authored-by: Brett Cannon <brett@python.org>
Signed-off-by: Christian Heimes <christian@python.org>
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@tiran @mdickinson @brettcannon
3 people committed Oct 24, 2021
commit ba5de5f8d080212d269c7e4fc51c20d5a9c45b82
6 changes: 1 addition & 5 deletions Makefile.pre.in
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Expand Up @@ -611,10 +611,6 @@ pybuilddir.txt: $(BUILDPYTHON)
exit 1 ; \
fi

# This is shared by the math and cmath modules
Modules/_math.o: Modules/_math.c Modules/_math.h
$(CC) -c $(CCSHARED) $(PY_CORE_CFLAGS) -o $@ $<

# blake2s is auto-generated from blake2b
$(srcdir)/Modules/_blake2/blake2s_impl.c: $(srcdir)/Modules/_blake2/blake2b_impl.c $(srcdir)/Modules/_blake2/blake2b2s.py
$(PYTHON_FOR_REGEN) $(srcdir)/Modules/_blake2/blake2b2s.py
Expand All @@ -625,7 +621,7 @@ $(srcdir)/Modules/_blake2/blake2s_impl.c: $(srcdir)/Modules/_blake2/blake2b_impl
# -s, --silent or --quiet is always the first char.
# Under BSD make, MAKEFLAGS might be " -s -v x=y".
# Ignore macros passed by GNU make, passed after --
sharedmods: $(BUILDPYTHON) pybuilddir.txt Modules/_math.o
sharedmods: $(BUILDPYTHON) pybuilddir.txt
@case "`echo X $$MAKEFLAGS | sed 's/^X //;s/ -- .*//'`" in \
*\ -s*|s*) quiet="-q";; \
*) quiet="";; \
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Build/2021-10-24-21-49-49.bpo-45548.UWx0UC.rst
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@@ -0,0 +1,3 @@
The :mod:`math` and :mod:`cmath` implementation now require a C99 compatible
``libm`` and no longer ship with workarounds for missing acosh, asinh,
expm1, and log1p functions.
4 changes: 2 additions & 2 deletions Modules/Setup
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Expand Up @@ -171,8 +171,8 @@ time timemodule.c
#array arraymodule.c
#audioop audioop.c
#binascii binascii.c
#cmath cmathmodule.c _math.c # -lm
#math mathmodule.c _math.c # -lm
#cmath cmathmodule.c # -lm
#math mathmodule.c # -lm
#pyexpat -I$(srcdir)/Modules/expat expat/xmlparse.c expat/xmlrole.c expat/xmltok.c pyexpat.c
#unicodedata unicodedata.c

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270 changes: 0 additions & 270 deletions Modules/_math.c
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57 changes: 20 additions & 37 deletions Modules/_math.h
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@@ -1,41 +1,24 @@
#ifdef HAVE_ACOSH
# define m_acosh acosh
#else
/* if the system doesn't have acosh, use the substitute
function defined in Modules/_math.c. */
double _Py_acosh(double x);
# define m_acosh _Py_acosh
#endif
/* log1p(x) = log(1+x). The log1p function is designed to avoid the
significant loss of precision that arises from direct evaluation when x is
small. Use the substitute from _math.c on all platforms: it includes
workarounds for buggy handling of zeros.
*/

#ifdef HAVE_ASINH
# define m_asinh asinh
#else
/* if the system doesn't have asinh, use the substitute
function defined in Modules/_math.c. */
double _Py_asinh(double x);
# define m_asinh _Py_asinh
#endif
static double
_Py_log1p(double x)
{
/* Some platforms supply a log1p function but don't respect the sign of
zero: log1p(-0.0) gives 0.0 instead of the correct result of -0.0.

#ifdef HAVE_ATANH
# define m_atanh atanh
#else
/* if the system doesn't have atanh, use the substitute
function defined in Modules/_math.c. */
double _Py_atanh(double x);
#define m_atanh _Py_atanh
#endif
To save fiddling with configure tests and platform checks, we handle the
special case of zero input directly on all platforms.
*/
if (x == 0.0) {
return x;
}
else {
return log1p(x);
}
}

#ifdef HAVE_EXPM1
# define m_expm1 expm1
#else
/* if the system doesn't have expm1, use the substitute
function defined in Modules/_math.c. */
double _Py_expm1(double x);
#define m_expm1 _Py_expm1
#endif

double _Py_log1p(double x);

/* Use the substitute from _math.c on all platforms:
it includes workarounds for buggy handling of zeros. */
#define m_log1p _Py_log1p
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