Merged revisions 68296,68299 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
........
r68296 | mark.dickinson | 2009-01-04 12:29:36 +0000 (Sun, 04 Jan 2009) | 6 lines
Add autoconf test to detect x87-style double rounding, as described in
issue #2937. This information can be helpful for diagnosing platform-
specific problems in math and cmath. The result of the test also
serves as a fairly reliable indicator of whether the x87 floating-point
instructions (as opposed to SSE2) are in use on Intel x86/x86_64 systems.
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r68299 | mark.dickinson | 2009-01-04 13:57:26 +0000 (Sun, 04 Jan 2009) | 4 lines
isinf and isnan are macros, not functions; fix configure script
to use AC_CHECK_DECLS instead of AC_CHECK_FUNCS for these.
(See discussion in issue #4506)
........
diff --git a/configure.in b/configure.in
index 394c804..d80e7a7 100644
--- a/configure.in
+++ b/configure.in
@@ -3056,6 +3056,44 @@
LIBS_SAVE=$LIBS
LIBS="$LIBS $LIBM"
+# Detect whether system arithmetic is subject to x87-style double
+# rounding issues. The result of this test has little meaning on non
+# IEEE 754 platforms. On IEEE 754, test should return 1 if rounding
+# mode is round-to-nearest and double rounding issues are present, and
+# 0 otherwise. See http://bugs.python.org/issue2937 for more info.
+AC_MSG_CHECKING(for x87-style double rounding)
+AC_CACHE_VAL(ac_cv_x87_double_rounding, [
+AC_TRY_RUN([
+#include <stdlib.h>
+#include <math.h>
+int main() {
+ volatile double x, y, z;
+ /* 1./(1-2**-53) -> 1+2**-52 (correct), 1.0 (double rounding) */
+ x = 0.99999999999999989; /* 1-2**-53 */
+ y = 1./x;
+ if (y != 1.)
+ exit(0);
+ /* 1e16+2.99999 -> 1e16+2. (correct), 1e16+4. (double rounding) */
+ x = 1e16;
+ y = 2.99999;
+ z = x + y;
+ if (z != 1e16+4.)
+ exit(0);
+ /* both tests show evidence of double rounding */
+ exit(1);
+}
+],
+ac_cv_x87_double_rounding=no,
+ac_cv_x87_double_rounding=yes,
+ac_cv_x87_double_rounding=no)])
+AC_MSG_RESULT($ac_cv_x87_double_rounding)
+if test "$ac_cv_x87_double_rounding" = yes
+then
+ AC_DEFINE(X87_DOUBLE_ROUNDING, 1,
+ [Define if arithmetic is subject to x87-style double rounding issue])
+fi
+
+
# On FreeBSD 6.2, it appears that tanh(-0.) returns 0. instead of
# -0. on some architectures.
AC_MSG_CHECKING(whether tanh preserves the sign of zero)
@@ -3084,7 +3122,8 @@
AC_REPLACE_FUNCS(hypot)
-AC_CHECK_FUNCS(acosh asinh atanh copysign expm1 finite isinf isnan log1p)
+AC_CHECK_FUNCS([acosh asinh atanh copysign expm1 finite log1p])
+AC_CHECK_DECLS([isinf, isnan, isfinite], [], [], [[#include <math.h>]])
LIBS=$LIBS_SAVE