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.
This commit is contained in:
Mark Dickinson
parent
d81780b8b0
commit
04b272336d
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@ -1,5 +1,5 @@
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#! /bin/sh
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# From configure.in Revision: 67463 .
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# From configure.in Revision: 68292 .
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# Guess values for system-dependent variables and create Makefiles.
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# Generated by GNU Autoconf 2.61 for python 2.7.
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#
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@ -2256,7 +2256,7 @@ echo $ECHO_N "checking for --without-gcc... $ECHO_C" >&6; }
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if test "${with_gcc+set}" = set; then
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withval=$with_gcc;
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case $withval in
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no) CC=cc
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no) CC=${CC:-cc}
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without_gcc=yes;;
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yes) CC=gcc
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without_gcc=no;;
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@ -21523,6 +21523,94 @@ fi
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LIBS_SAVE=$LIBS
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LIBS="$LIBS $LIBM"
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# Detect whether system arithmetic is subject to x87-style double
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# rounding issues. The result of this test has little meaning on non
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# IEEE 754 platforms. On IEEE 754, test should return 1 if rounding
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# mode is round-to-nearest and double rounding issues are present, and
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# 0 otherwise. See http://bugs.python.org/issue2937 for more info.
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{ echo "$as_me:$LINENO: checking for x87-style double rounding" >&5
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echo $ECHO_N "checking for x87-style double rounding... $ECHO_C" >&6; }
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if test "${ac_cv_x87_double_rounding+set}" = set; then
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echo $ECHO_N "(cached) $ECHO_C" >&6
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else
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if test "$cross_compiling" = yes; then
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ac_cv_x87_double_rounding=no
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else
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cat >conftest.$ac_ext <<_ACEOF
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/* confdefs.h. */
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_ACEOF
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cat confdefs.h >>conftest.$ac_ext
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cat >>conftest.$ac_ext <<_ACEOF
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/* end confdefs.h. */
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#include <stdlib.h>
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#include <math.h>
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int main() {
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volatile double x, y, z;
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/* 1./(1-2**-53) -> 1+2**-52 (correct), 1.0 (double rounding) */
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x = 0.99999999999999989; /* 1-2**-53 */
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y = 1./x;
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if (y != 1.)
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exit(0);
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/* 1e16+2.99999 -> 1e16+2. (correct), 1e16+4. (double rounding) */
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x = 1e16;
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y = 2.99999;
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z = x + y;
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if (z != 1e16+4.)
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exit(0);
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/* both tests show evidence of double rounding */
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exit(1);
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}
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_ACEOF
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rm -f conftest$ac_exeext
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if { (ac_try="$ac_link"
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case "(($ac_try" in
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*\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
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*) ac_try_echo=$ac_try;;
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esac
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eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
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(eval "$ac_link") 2>&5
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ac_status=$?
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echo "$as_me:$LINENO: \$? = $ac_status" >&5
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(exit $ac_status); } && { ac_try='./conftest$ac_exeext'
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{ (case "(($ac_try" in
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*\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
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*) ac_try_echo=$ac_try;;
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esac
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eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5
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(eval "$ac_try") 2>&5
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ac_status=$?
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echo "$as_me:$LINENO: \$? = $ac_status" >&5
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(exit $ac_status); }; }; then
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ac_cv_x87_double_rounding=no
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else
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echo "$as_me: program exited with status $ac_status" >&5
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echo "$as_me: failed program was:" >&5
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sed 's/^/| /' conftest.$ac_ext >&5
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( exit $ac_status )
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ac_cv_x87_double_rounding=yes
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fi
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rm -f core *.core core.conftest.* gmon.out bb.out conftest$ac_exeext conftest.$ac_objext conftest.$ac_ext
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fi
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fi
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{ echo "$as_me:$LINENO: result: $ac_cv_x87_double_rounding" >&5
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echo "${ECHO_T}$ac_cv_x87_double_rounding" >&6; }
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if test "$ac_cv_x87_double_rounding" = yes
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then
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cat >>confdefs.h <<\_ACEOF
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#define X87_DOUBLE_ROUNDING 1
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_ACEOF
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fi
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# On FreeBSD 6.2, it appears that tanh(-0.) returns 0. instead of
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# -0. on some architectures.
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{ echo "$as_me:$LINENO: checking whether tanh preserves the sign of zero" >&5
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38
configure.in
38
configure.in
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@ -3143,6 +3143,44 @@ fi],
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LIBS_SAVE=$LIBS
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LIBS="$LIBS $LIBM"
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# Detect whether system arithmetic is subject to x87-style double
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# rounding issues. The result of this test has little meaning on non
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# IEEE 754 platforms. On IEEE 754, test should return 1 if rounding
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# mode is round-to-nearest and double rounding issues are present, and
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# 0 otherwise. See http://bugs.python.org/issue2937 for more info.
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AC_MSG_CHECKING(for x87-style double rounding)
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AC_CACHE_VAL(ac_cv_x87_double_rounding, [
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AC_TRY_RUN([
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#include <stdlib.h>
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#include <math.h>
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int main() {
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volatile double x, y, z;
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/* 1./(1-2**-53) -> 1+2**-52 (correct), 1.0 (double rounding) */
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x = 0.99999999999999989; /* 1-2**-53 */
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y = 1./x;
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if (y != 1.)
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exit(0);
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/* 1e16+2.99999 -> 1e16+2. (correct), 1e16+4. (double rounding) */
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x = 1e16;
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y = 2.99999;
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z = x + y;
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if (z != 1e16+4.)
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exit(0);
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/* both tests show evidence of double rounding */
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exit(1);
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}
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],
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ac_cv_x87_double_rounding=no,
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ac_cv_x87_double_rounding=yes,
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ac_cv_x87_double_rounding=no)])
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AC_MSG_RESULT($ac_cv_x87_double_rounding)
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if test "$ac_cv_x87_double_rounding" = yes
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then
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AC_DEFINE(X87_DOUBLE_ROUNDING, 1,
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[Define if arithmetic is subject to x87-style double rounding issue])
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fi
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# On FreeBSD 6.2, it appears that tanh(-0.) returns 0. instead of
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# -0. on some architectures.
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AC_MSG_CHECKING(whether tanh preserves the sign of zero)
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@ -983,6 +983,9 @@
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first (like Motorola and SPARC, unlike Intel and VAX). */
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#undef WORDS_BIGENDIAN
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/* Define if arithmetic is subject to x87-style double rounding issue */
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#undef X87_DOUBLE_ROUNDING
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/* Define to 1 if on AIX 3.
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System headers sometimes define this.
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We just want to avoid a redefinition error message. */
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