Use LUT for group indexes instead of calculating on-the-fly

lut.h

@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2022 Camden Dixie O'Brien
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 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
+ * Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public
+ * License along with this program.  If not, see
+ * <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef LUT_H
+#define LUT_H
+
+#include "sud.h"
+
+#define NGROUP (NDIGITS - 1)
+
+extern const unsigned rowidx_lut[NCELLS][NGROUP];
+extern const unsigned colidx_lut[NCELLS][NGROUP];
+extern const unsigned segidx_lut[NCELLS][NGROUP];
+
+#endif