modf-ieee: Work around test failures on *BSD, IRIX, OSF/1, Cygwin. * m4/modf-ieee.m4: New file. * m4/modf.m4 (gl_FUNC_MODF): If gl_FUNC_MODF_IEEE is present, test whether modf works with NaN and Inf. Replace it if not. * lib/math.in.h (modf): New declaration. * lib/modf.c: New file. * m4/math_h.m4 (gl_MATH_H): Test whether modf is declared. (gl_MATH_H_DEFAULTS): Initialize GNULIB_MODF, REPLACE_MODF. * modules/math (Makefile.am): Substitute GNULIB_MODF, REPLACE_MODF. * modules/modf (Files): Add lib/modf.c. (Depends-on): Add math, isfinite, trunc, isinf. (configure.ac): Addrange to compile lib/modf.c if needed. * modules/modf-ieee (Files): Add m4/modf-ieee.m4, m4/minus-zero.m4, m4/signbit.m4. (configure.ac): Invoke gl_FUNC_MODF_IEEE. * tests/test-math-c++.cc: Check the declaration of modf. * doc/posix-functions/modf.texi: Mention the modf-ieee module.

--- a/tests/test-math-c++.cc
+++ b/tests/test-math-c++.cc
@@ -195,7 +195,9 @@
 #if GNULIB_TEST_MODFF
 SIGNATURE_CHECK (GNULIB_NAMESPACE::modff, float, (float, float *));
 #endif
-//SIGNATURE_CHECK (GNULIB_NAMESPACE::modf, double, (double, double *));
+#if GNULIB_TEST_MODF
+SIGNATURE_CHECK (GNULIB_NAMESPACE::modf, double, (double, double *));
+#endif
 #if GNULIB_TEST_MODFL
 SIGNATURE_CHECK (GNULIB_NAMESPACE::modfl, long double,
                  (long double, long double *));