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

not reliable yet

extern/fftw/api/version.c

@@ -0,0 +1,88 @@
+/*
+ * 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 "api/api.h"
+
+const char X(cc)[] = FFTW_CC;
+
+/* fftw <= 3.2.2 had special compiler flags for codelets, which are
+   not used anymore.  We keep this variable around because it is part
+   of the ABI */
+const char X(codelet_optim)[] = "";
+
+const char X(version)[] = PACKAGE "-" PACKAGE_VERSION
+
+#if HAVE_FMA
+   "-fma"
+#endif
+
+#if HAVE_SSE2
+   "-sse2"
+#endif
+
+  /* Earlier versions of FFTW only provided 256-bit AVX, which meant
+   * it was important to also enable sse2 for best performance for
+   * short transforms. Since some programs check for this and warn
+   * the user, we explicitly add avx_128 to the suffix to emphasize
+   * that this version is more capable.
+   */
+
+#if HAVE_AVX
+   "-avx"
+#endif
+
+#if HAVE_AVX_128_FMA
+   "-avx_128_fma"
+#endif
+
+#if HAVE_AVX2
+   "-avx2-avx2_128"
+#endif
+
+#if HAVE_AVX512
+   "-avx512"
+#endif
+
+#if HAVE_KCVI
+   "-kcvi"
+#endif
+
+#if HAVE_ALTIVEC
+   "-altivec"
+#endif
+
+#if HAVE_VSX
+   "-vsx"
+#endif
+
+#if HAVE_NEON
+   "-neon"
+#endif
+
+#if defined(HAVE_GENERIC_SIMD128)
+   "-generic_simd128"
+#endif
+
+#if defined(HAVE_GENERIC_SIMD256)
+   "-generic_simd256"
+#endif
+
+;