bpo-45440: Require math.h isinf() to build (GH-28894)

Building Python now requires a C99 <math.h> header file providing
isinf(), isnan() and isfinite() functions.

Remove the Py_FORCE_DOUBLE() macro. It was used by the
Py_IS_INFINITY() macro.

Changes:

* Remove Py_IS_NAN(), Py_IS_INFINITY() and Py_IS_FINITE()
  in PC/pyconfig.h.
* Remove the _Py_force_double() function.
* configure no longer checks if math.h defines isinf(), isnan() and
  isfinite().

1 files changed, 9 insertions, 71 deletions

diff --git a/Include/pymath.h b/Include/pymath.h
index d688e50..57310fc 100644
--- a/Include/pymath.h
+++ b/Include/pymath.h
@@ -4,8 +4,6 @@
 #ifndef Py_PYMATH_H
 #define Py_PYMATH_H
 
-#include "pyconfig.h"             // HAVE_DECL_ISNAN
-
 /* High precision definition of pi and e (Euler)
  * The values are taken from libc6's math.h.
  */
@@ -29,77 +27,17 @@
 #define Py_MATH_TAU 6.2831853071795864769252867665590057683943L
 #endif
 
+// Py_IS_NAN(X)
+// Return 1 if float or double arg is a NaN, else 0.
+#define Py_IS_NAN(X) isnan(X)
 
-/* On x86, Py_FORCE_DOUBLE forces a floating-point number out of an x87 FPU
-   register and into a 64-bit memory location, rounding from extended
-   precision to double precision in the process.  On other platforms it does
-   nothing. */
-
-/* we take double rounding as evidence of x87 usage */
-#ifndef Py_LIMITED_API
-#ifndef Py_FORCE_DOUBLE
-#  ifdef X87_DOUBLE_ROUNDING
-PyAPI_FUNC(double) _Py_force_double(double);
-#    define Py_FORCE_DOUBLE(X) (_Py_force_double(X))
-#  else
-#    define Py_FORCE_DOUBLE(X) (X)
-#  endif
-#endif
-#endif
-
-/* Py_IS_NAN(X)
- * Return 1 if float or double arg is a NaN, else 0.
- * Caution:
- *     X is evaluated more than once.
- *     This may not work on all platforms.  Each platform has *some*
- *     way to spell this, though -- override in pyconfig.h if you have
- *     a platform where it doesn't work.
- * Note: PC/pyconfig.h defines Py_IS_NAN as _isnan
- */
-#ifndef Py_IS_NAN
-#  if defined HAVE_DECL_ISNAN && HAVE_DECL_ISNAN == 1
-#    define Py_IS_NAN(X) isnan(X)
-#  else
-#    define Py_IS_NAN(X) ((X) != (X))
-#  endif
-#endif
-
-/* Py_IS_INFINITY(X)
- * Return 1 if float or double arg is an infinity, else 0.
- * Caution:
- *    X is evaluated more than once.
- *    This implementation may set the underflow flag if |X| is very small;
- *    it really can't be implemented correctly (& easily) before C99.
- *    Override in pyconfig.h if you have a better spelling on your platform.
- *  Py_FORCE_DOUBLE is used to avoid getting false negatives from a
- *    non-infinite value v sitting in an 80-bit x87 register such that
- *    v becomes infinite when spilled from the register to 64-bit memory.
- * Note: PC/pyconfig.h defines Py_IS_INFINITY as _isinf
- */
-#ifndef Py_IS_INFINITY
-#  if defined HAVE_DECL_ISINF && HAVE_DECL_ISINF == 1
-#    define Py_IS_INFINITY(X) isinf(X)
-#  else
-#    define Py_IS_INFINITY(X) ((X) &&                                   \
-                               (Py_FORCE_DOUBLE(X)*0.5 == Py_FORCE_DOUBLE(X)))
-#  endif
-#endif
+// Py_IS_INFINITY(X)
+// Return 1 if float or double arg is an infinity, else 0.
+#define Py_IS_INFINITY(X) isinf(X)
 
-/* Py_IS_FINITE(X)
- * Return 1 if float or double arg is neither infinite nor NAN, else 0.
- * Some compilers (e.g. VisualStudio) have intrinsics for this, so a special
- * macro for this particular test is useful
- * Note: PC/pyconfig.h defines Py_IS_FINITE as _finite
- */
-#ifndef Py_IS_FINITE
-#  if defined HAVE_DECL_ISFINITE && HAVE_DECL_ISFINITE == 1
-#    define Py_IS_FINITE(X) isfinite(X)
-#  elif defined HAVE_FINITE
-#    define Py_IS_FINITE(X) finite(X)
-#  else
-#    define Py_IS_FINITE(X) (!Py_IS_INFINITY(X) && !Py_IS_NAN(X))
-#  endif
-#endif
+// Py_IS_FINITE(X)
+// Return 1 if float or double arg is neither infinite nor NAN, else 0.
+#define Py_IS_FINITE(X) isfinite(X)
 
 /* HUGE_VAL is supposed to expand to a positive double infinity.  Python
  * uses Py_HUGE_VAL instead because some platforms are broken in this