From a366b3ac4f5c3e64987adf2b6ef8db6dfae9faef Mon Sep 17 00:00:00 2001
From: Jared Boone <jboone@earfeast.com>
Date: Fri, 6 Nov 2015 13:49:59 -0800
Subject: [PATCH] CRC class.

Has some more efficient code, commented out because I was having trouble getting it to work. However, it may have been due to the particular data I was trying to decode and CRC-validate.
---
 firmware/common/crc.hpp | 104 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 104 insertions(+)
 create mode 100644 firmware/common/crc.hpp

diff --git a/firmware/common/crc.hpp b/firmware/common/crc.hpp
new file mode 100644
index 000000000..0b825dc22
--- /dev/null
+++ b/firmware/common/crc.hpp
@@ -0,0 +1,104 @@
+/*
+ * Copyright (C) 2014 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 __CRC_H__
+#define __CRC_H__
+
+#include <cstddef>
+#include <cstdint>
+
+template<typename T>
+class CRC {
+public:
+	constexpr CRC(
+		const T polynomial/*,
+		const T initial*/
+	) : polynomial { polynomial }/*,
+		initial { initial }*/
+	{
+		// CRC LSB must always be 1
+	}
+/*
+	template<typename U>
+	T calculate(const U& bits, const size_t length) {
+		if( length > bits.size() ) {
+			// Exception.
+			return 0;
+		}
+
+		T crc = 0;
+
+		for(size_t i=0; i<length; i++) {
+			crc = feed_bit(crc, bits[i]);
+		}
+
+		return crc;
+	}
+*/
+	T calculate_byte(const T crc_in, const uint8_t data) {
+		/* Inspired by
+		 * http://www.barrgroup.com/Embedded-Systems/How-To/CRC-Calculation-C-Code
+		 */
+		T remainder = crc_in;
+		remainder ^= data << (width() - 8);
+		for(size_t bit=8; bit>0; --bit) {
+			if( remainder & top_bit() ) {
+				remainder = (remainder << 1) ^ polynomial;
+			} else {
+				remainder = (remainder << 1);
+			}
+		}
+		return remainder;
+	}
+/*
+	T calculate(const uint8_t* const data, const size_t length) {
+		T remainder = initial;
+		for(size_t byte=0; byte<length; ++byte) {
+			remainder = calculate_byte(remainder, data[byte]);
+		}
+		return remainder;
+	}
+*/
+private:
+	const T polynomial;
+//	const T initial;
+
+	static constexpr size_t width() {
+		return 8 * sizeof(T);
+	}
+
+	static constexpr T top_bit() {
+		return 1U << (width() - 1);
+	}
+/*
+	T feed_bit(const T crc_in, const uint_fast8_t bit) {
+		T crc_out = crc_in ^ (bit & 1);
+		if( crc_in & top_bit() ) {
+			return ((crc_in << 1) | (bit & 1)) ^ polynomial;
+		} else {
+			return (crc_in << 1) | (bit & 1);
+		}
+	}
+*/
+};
+
+
+#endif/*__CRC_H__*/