+ 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