Add LFSR random number generator.

Used for SD card write/read testing, maybe other stuff eventually?

firmware/common/lfsr_random.hpp

@@ -0,0 +1,34 @@
+/*
+ * Copyright (C) 2015 Jared Boone, ShareBrained Technology, Inc.
+ *
+ * This file is part of PortaPack.
+ *
+ * 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, 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; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __LFSR_RANDOM_HPP__
+#define __LFSR_RANDOM_HPP__
+
+#include <cstdint>
+#include <cstddef>
+
+using lfsr_word_t = uint32_t;
+
+lfsr_word_t lfsr_iterate(lfsr_word_t v);
+void lfsr_fill(lfsr_word_t& v, lfsr_word_t* buffer, size_t word_count);
+bool lfsr_compare(lfsr_word_t& v, const lfsr_word_t* buffer, size_t word_count);
+
+#endif/*__LFSR_RANDOM_HPP__*/