[Python-checkins] r69459 - in python/trunk: Include/pymath.h Misc/NEWS Python/pymath.c
mark.dickinson
python-checkins at python.org
Mon Feb 9 15:18:43 CET 2009
Author: mark.dickinson
Date: Mon Feb 9 15:18:43 2009
New Revision: 69459
Log:
Issue #4575: fix Py_IS_INFINITY macro to work correctly on x87 FPUs.
It now forces its argument to double before testing for infinity.
Modified:
python/trunk/Include/pymath.h
python/trunk/Misc/NEWS
python/trunk/Python/pymath.c
Modified: python/trunk/Include/pymath.h
==============================================================================
--- python/trunk/Include/pymath.h (original)
+++ python/trunk/Include/pymath.h Mon Feb 9 15:18:43 2009
@@ -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)
Modified: python/trunk/Misc/NEWS
==============================================================================
--- python/trunk/Misc/NEWS (original)
+++ python/trunk/Misc/NEWS Mon Feb 9 15:18:43 2009
@@ -12,6 +12,9 @@
Core and Builtins
-----------------
+- 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 #4978: Passing keyword arguments as unicode strings is now allowed.
- Issue 1242657: the __len__() and __length_hint__() calls in several tools
Modified: python/trunk/Python/pymath.c
==============================================================================
--- python/trunk/Python/pymath.c (original)
+++ python/trunk/Python/pymath.c Mon Feb 9 15:18:43 2009
@@ -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)
{
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