From f76750e55b48340321c0305aaef68acf18c45e29 Mon Sep 17 00:00:00 2001
From: Jared Boone <jboone@earfeast.com>
Date: Sun, 10 Apr 2016 16:30:28 -0700
Subject: [PATCH] Add LFSR random number generator.

Used for SD card write/read testing, maybe other stuff eventually?
---
 firmware/common/lfsr_random.cpp | 106 ++++++++++++++++++++++++++++++++
 firmware/common/lfsr_random.hpp |  34 ++++++++++
 2 files changed, 140 insertions(+)
 create mode 100644 firmware/common/lfsr_random.cpp
 create mode 100644 firmware/common/lfsr_random.hpp

diff --git a/firmware/common/lfsr_random.cpp b/firmware/common/lfsr_random.cpp
new file mode 100644
index 000000000..ddeb044a1
--- /dev/null
+++ b/firmware/common/lfsr_random.cpp
@@ -0,0 +1,106 @@
+/*
+ * 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.
+ */
+
+#include "lfsr_random.hpp"
+
+static void lfsr_iterate_internal(lfsr_word_t& v)
+{
+	/*
+	    Generated with lfsr-generator:
+	    http://lfsr-generator.sourceforge.net
+	    =============================================
+		config          : fibonacci
+		length          : 31
+		taps            : (31, 18)
+		shift-amounts   : (12, 12, 8)
+		shift-direction : left
+	*/
+	enum {
+		length         = 31,
+		tap_0          = 31,
+		tap_1          = 18,
+		shift_amount_0 = 12,
+		shift_amount_1 = 12,
+		shift_amount_2 =  8
+	};
+
+	const lfsr_word_t zero = 0;
+	v = (
+		(
+			v << shift_amount_0
+		) | (
+			(
+				(v >> (tap_0 - shift_amount_0)) ^
+				(v >> (tap_1 - shift_amount_0))
+			) & (
+				~(~zero << shift_amount_0)
+			)
+		)
+	);
+	v = (
+		(
+			v << shift_amount_1
+		) | (
+			(
+				(v >> (tap_0 - shift_amount_1)) ^
+				(v >> (tap_1 - shift_amount_1))
+			) & (
+				~(~zero << shift_amount_1)
+			)
+		)
+	);
+	v = (
+		(
+			v << shift_amount_2
+		) | (
+			(
+				(v >> (tap_0 - shift_amount_2)) ^
+				(v >> (tap_1 - shift_amount_2))
+			) & (
+				~(~zero << shift_amount_2)
+			)
+		)
+	);
+}
+
+lfsr_word_t lfsr_iterate(lfsr_word_t v) {
+	lfsr_iterate_internal(v);
+	return v;
+}
+
+void lfsr_fill(lfsr_word_t& v, lfsr_word_t* buffer, size_t word_count) {
+	while( word_count != 0 ) {
+		lfsr_iterate_internal(v);
+		*(buffer++) = v;
+		word_count--;
+	}
+}
+
+bool lfsr_compare(lfsr_word_t& v, const lfsr_word_t* buffer, size_t word_count) {
+	while( word_count != 0 ) {
+		lfsr_iterate_internal(v);
+		if( *(buffer++) != v ) {
+			return false;
+		}
+		word_count--;
+	}
+	return true;
+}
diff --git a/firmware/common/lfsr_random.hpp b/firmware/common/lfsr_random.hpp
new file mode 100644
index 000000000..0eaadc192
--- /dev/null
+++ b/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__*/