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firmware/common/field_reader.hpp

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+/*
+ * 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 __FIELD_READER_H__
+#define __FIELD_READER_H__
+
+#include <cstdint>
+#include <cstddef>
+
+struct BitRemapNone {
+	constexpr size_t operator()(const size_t& bit_index) const {
+		return bit_index;
+	}
+};
+
+struct BitRemapByteReverse {
+	constexpr size_t operator()(const size_t bit_index) const {
+		return bit_index ^ 7;
+	}
+};
+
+template<typename T, typename BitRemap>
+class FieldReader {
+public:
+	constexpr FieldReader(
+		const T& data
+	) : data { data }
+	{
+	}
+
+	/* The "start_bit" winds up being the MSB of the returned field value. */
+	/* The BitRemap functor determines which bits are read from the source
+	 * packet. */
+	uint32_t read(const size_t start_bit, const size_t length) const {
+		uint32_t value = 0;
+		for(size_t i=start_bit; i<(start_bit + length); i++) {
+			value = (value << 1) | data[bit_remap(i)];
+		}
+		return value;
+	}
+
+private:
+	const T& data;
+	const BitRemap bit_remap { };
+};
+
+#endif/*__FIELD_READER_H__*/