GUI: try using FFTW for per-chan osc wave center

not reliable yet

extern/fftw/kernel/problem.c

@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2003, 2007-14 Matteo Frigo
+ * Copyright (c) 2003, 2007-14 Massachusetts Institute of Technology
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ */
+
+
+#include "kernel/ifftw.h"
+
+/* constructor */
+problem *X(mkproblem)(size_t sz, const problem_adt *adt)
+{
+     problem *p = (problem *)MALLOC(sz, PROBLEMS);
+
+     p->adt = adt;
+     return p;
+}
+
+/* destructor */
+void X(problem_destroy)(problem *ego)
+{
+     if (ego)
+	  ego->adt->destroy(ego);
+}
+
+/* management of unsolvable problems */
+static void unsolvable_destroy(problem *ego)
+{
+     UNUSED(ego);
+}
+
+static void unsolvable_hash(const problem *p, md5 *m)
+{
+     UNUSED(p);
+     X(md5puts)(m, "unsolvable");
+}
+
+static void unsolvable_print(const problem *ego, printer *p)
+{
+     UNUSED(ego);
+     p->print(p, "(unsolvable)");
+}
+
+static void unsolvable_zero(const problem *ego)
+{
+     UNUSED(ego);
+}
+
+static const problem_adt padt =
+{
+     PROBLEM_UNSOLVABLE,
+     unsolvable_hash,
+     unsolvable_zero,
+     unsolvable_print,
+     unsolvable_destroy
+};
+
+/* there is no point in malloc'ing this one */
+static problem the_unsolvable_problem = { &padt };
+
+problem *X(mkproblem_unsolvable)(void)
+{
+     return &the_unsolvable_problem;
+}