On NetBSD 3.0/x86, the round() function exists but yields 1.0 (instead of 0.0)
for x = 1/2 - 2^-54. This is noticed by test-round2.
This patch fixes it by testing for this bug in the autoconf macro.
2007-11-11 Bruno Haible <[EMAIL PROTECTED]>
* m4/round.m4 (gl_FUNC_ROUND): Test against NetBSD 3.0 bug.
* doc/functions/round.texi: Mention the NetBSD 3.0 bug.
*** doc/functions/round.texi.orig 2007-11-11 15:10:10.000000000 +0100
--- doc/functions/round.texi 2007-11-11 14:52:32.000000000 +0100
***************
*** 11,16 ****
--- 11,19 ----
@item
This function is missing on some platforms:
FreeBSD 5.2.1, OpenBSD 3.8, AIX 5.1, IRIX 6.5, OSF/1 4.0, Solaris 9, Interix
3.5.
+ @item
+ This functions returns a wrong result for x = 1/2 - 2^-54 on some platforms:
+ NetBSD 3.0.
@end itemize
Portability problems not fixed by Gnulib:
*** m4/round.m4.orig 2007-11-11 15:10:11.000000000 +0100
--- m4/round.m4 2007-11-11 14:52:39.000000000 +0100
***************
*** 1,4 ****
! # round.m4 serial 4
dnl Copyright (C) 2007 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
--- 1,4 ----
! # round.m4 serial 5
dnl Copyright (C) 2007 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
***************
*** 13,18 ****
--- 13,56 ----
if test "$ac_cv_have_decl_round" = yes; then
gl_CHECK_MATH_LIB([ROUND_LIBM], [x = round (x);])
fi
+ if test "$ac_cv_have_decl_round" = yes && test "$ROUND_LIBM" != missing;
then
+ dnl Test whether round() produces correct results. On NetBSD 3.0, for
+ dnl x = 1/2 - 2^-54, the system's round() returns a wrong result.
+ AC_REQUIRE([AC_PROG_CC])
+ AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+ AC_CACHE_CHECK([whether round works], [gl_cv_func_round_works],
+ [
+ save_LIBS="$LIBS"
+ LIBS="$LIBS $ROUND_LIBM"
+ AC_TRY_RUN([
+ #include <float.h>
+ #include <math.h>
+ int main()
+ {
+ /* 2^DBL_MANT_DIG. */
+ static const double TWO_MANT_DIG =
+ /* Assume DBL_MANT_DIG <= 5 * 31.
+ Use the identity
+ n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5). */
+ (double) (1U << (DBL_MANT_DIG / 5))
+ * (double) (1U << ((DBL_MANT_DIG + 1) / 5))
+ * (double) (1U << ((DBL_MANT_DIG + 2) / 5))
+ * (double) (1U << ((DBL_MANT_DIG + 3) / 5))
+ * (double) (1U << ((DBL_MANT_DIG + 4) / 5));
+ volatile double x = 0.5 - 0.5 / TWO_MANT_DIG;
+ exit (x < 0.5 && round (x) != 0.0);
+ }], [gl_cv_func_round_works=yes], [gl_cv_func_round_works=no],
+ [case "$host_os" in
+ netbsd*) gl_cv_func_round_works="guessing no";;
+ *) gl_cv_func_round_works="guessing yes";;
+ esac
+ ])
+ LIBS="$save_LIBS"
+ ])
+ case "$gl_cv_func_round_works" in
+ *no) ROUND_LIBM=missing ;;
+ esac
+ fi
if test "$ac_cv_have_decl_round" != yes || test "$ROUND_LIBM" = missing;
then
REPLACE_ROUND=1
AC_LIBOBJ([round])
