Issue #5724: Fix cmath failures on Solaris 10.

Author: mdickinson

Include/pymath.h

@@ -77,6 +77,21 @@ extern double copysign(double, double);
 #define Py_MATH_E 2.7182818284590452354
 #endif
 
+/* 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_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
+
 /* Py_IS_NAN(X)
  * Return 1 if float or double arg is a NaN, else 0.
  * Caution:
@@ -87,7 +102,7 @@ extern double copysign(double, double);
  * Note: PC/pyconfig.h defines Py_IS_NAN as _isnan
  */
 #ifndef Py_IS_NAN
-#ifdef HAVE_ISNAN
+#if defined HAVE_DECL_ISNAN && HAVE_DECL_ISNAN == 1
 #define Py_IS_NAN(X) isnan(X)
 #else
 #define Py_IS_NAN(X) ((X) != (X))
@@ -101,14 +116,18 @@ extern double copysign(double, double);
  *    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
-#ifdef HAVE_ISINF
-#define Py_IS_INFINITY(X) isinf(X)
-#else
-#define Py_IS_INFINITY(X) ((X) && (X)*0.5 == (X))
-#endif
+#  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_FINITE(X)
@@ -118,7 +137,9 @@ extern double copysign(double, double);
  * Note: PC/pyconfig.h defines Py_IS_FINITE as _finite
  */
 #ifndef Py_IS_FINITE
-#ifdef HAVE_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))

Misc/NEWS

@@ -12,6 +12,10 @@ What's New in Python 2.6.3
 Core and Builtins
 -----------------
 
+- Issue #5724: (See also issue #4575.) Fix Py_IS_INFINITY macro to
+  work correctly on x87 FPUs: it now forces its argument to double
+  before testing for infinity.
+
 - Issue #4971: Fix titlecase for characters that are their own
   titlecase, but not their own uppercase.
 

PC/pyconfig.h

@@ -405,11 +405,11 @@ Py_NO_ENABLE_SHARED to find out.  Also support MS_NO_COREDLL for b/w compat */
 /* Define to 1 if you have the `copysign' function. */
 #define HAVE_COPYSIGN 1
 
-/* Define to 1 if you have the `isinf' function. */
-#define HAVE_ISINF 1
+/* Define to 1 if you have the `isinf' macro. */
+#define HAVE_DECL_ISINF 1
 
 /* Define to 1 if you have the `isnan' function. */
-#define HAVE_ISNAN 1
+#define HAVE_DECL_ISNAN 1
 
 /* Define if on AIX 3.
    System headers sometimes define this.

Python/pymath.c

@@ -1,5 +1,18 @@
 #include "Python.h"
 
+#ifdef X87_DOUBLE_ROUNDING
+/* On x86 platforms using an x87 FPU, this function is called from the
+   Py_FORCE_DOUBLE macro (defined in pymath.h) to force a floating-point
+   number out of an 80-bit x87 FPU register and into a 64-bit memory location,
+   thus rounding from extended precision to double precision. */
+double _Py_force_double(double x)
+{
+	volatile double y;
+	y = x;
+	return y;
+}
+#endif
+
 #ifndef HAVE_HYPOT
 double hypot(double x, double y)
 {