Merged revisions 69459 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
........
r69459 | mark.dickinson | 2009-02-09 14:18:43 +0000 (Mon, 09 Feb 2009) | 3 lines
Issue #4575: fix Py_IS_INFINITY macro to work correctly on x87 FPUs.
It now forces its argument to double before testing for infinity.
........
diff --git a/Include/pymath.h b/Include/pymath.h
index 0631b93..6ad174d 100644
--- a/Include/pymath.h
+++ b/Include/pymath.h
@@ -77,6 +77,21 @@
#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:
@@ -101,14 +116,18 @@
* 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) && (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)