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common/crc_slow.h

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+/* ScummVM - Graphic Adventure Engine
+ *
+ * ScummVM is the legal property of its developers, whose names
+ * are too numerous to list here. Please refer to the COPYRIGHT
+ * file distributed with this source distribution.
+ *
+ * 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 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+/**********************************************************************
+ *
+ * Filename:    crc.c
+ *
+ * Description: Slow implementation of the CRC standards.
+ *
+ * Notes:
+ *
+ *
+ * Copyright (c) 2000 by Michael Barr.  This software is placed into
+ * the public domain and may be used for any purpose.  However, this
+ * notice must not be changed or removed and no warranty is either
+ * expressed or implied by its publication or distribution.
+ **********************************************************************/
+
+#ifndef COMMON_CRC_SLOW_H
+#define COMMON_CRC_SLOW_H
+
+#include "common/system.h" // For types.
+
+namespace Common {
+
+template <typename T>
+class CRCSlow {
+public:
+	CRCSlow(T poly, T init_remainder, T final_xor, bool need_reflect);
+	T crcSlow(byte const message[], int nBytes) const;
+
+protected:
+	const T _poly;
+	const T _init_remainder;
+	const T _final_xor;
+
+	const int _width;
+	const int _topbit;
+
+	const bool _reflect;
+
+	template<typename R>
+	static R reflect(R data);
+
+	byte reflectData(byte x) const { return _reflect ? reflect<byte>(x) : x; }
+	T reflectRemainder(T x) const { return _reflect ? reflect<T>(x) : x; }
+};
+
+/*********************************************************************
+ *
+ * Function:    reflect()
+ *
+ * Description: Reorder the bits of a binary sequence, by reflecting
+ *              them about the middle position.
+ *
+ * Notes:       No checking is done that nBits <= 32.
+ *
+ * Returns:     The reflection of the original data.
+ *
+ *********************************************************************/
+template<typename T> template<typename R>
+R CRCSlow<T>::reflect(R data) {
+	R reflection = 0;
+
+	/*
+	 * Reflect the data about the center bit.
+	 */
+	for (byte bit = 0; bit < sizeof(R) * 8; ++bit) {
+		/*
+		 * If the LSB bit is set, set the reflection of it.
+		 */
+		if (data & 0x01) {
+			reflection |= (1 << ((sizeof(R) * 8 - 1) - bit));
+		}
+
+		data = (data >> 1);
+	}
+
+	return reflection;
+}
+
+
+/*********************************************************************
+ *
+ * Function:    crcSlow()
+ *
+ * Description: Compute the CRC of a given message.
+ *
+ * Notes:
+ *
+ * Returns:     The CRC of the message.
+ *
+ *********************************************************************/
+template<typename T>
+T CRCSlow<T>::crcSlow(byte const message[], int nBytes) const {
+	T remainder = _init_remainder;
+
+	/*
+	 * Perform modulo-2 division, a byte at a time.
+	 */
+	for (int b = 0; b < nBytes; ++b) {
+		/*
+		 * Bring the next byte into the remainder.
+		 */
+		remainder ^= reflectData(message[b]) << (_width - 8);
+
+		/*
+		 * Perform modulo-2 division, a bit at a time.
+		 */
+		for (byte bit = 8; bit > 0; --bit) {
+			/*
+			 * Try to divide the current data bit.
+			 */
+			if (remainder & _topbit) {
+				remainder = (remainder << 1) ^ _poly;
+			} else {
+				remainder = (remainder << 1);
+			}
+		}
+	}
+
+	/*
+	 * The final remainder is the CRC result.
+	 */
+	return reflectRemainder(remainder) ^ _final_xor;
+}
+
+
+template<typename T>
+CRCSlow<T>::CRCSlow(T poly, T init_remainder, T final_xor, bool need_reflect) :
+	_poly(poly), _init_remainder(init_remainder), _final_xor(final_xor), _width(8 * sizeof(T)), _topbit(1 << (8 * sizeof(T) - 1)), _reflect(need_reflect) {}
+
+class CRC_CCITT_Slow : public CRCSlow<uint16> {
+public:
+	CRC_CCITT_Slow() : CRCSlow<uint16>(0x1021, 0xFFFF, 0x0000, false) {}
+};
+
+class CRC_BINHEX_Slow : public CRCSlow<uint16> {
+public:
+	CRC_BINHEX_Slow() : CRCSlow<uint16>(0x1021, 0x0000, 0x0000, false) {}
+};
+
+class CRC16_Slow : public CRCSlow<uint16> {
+public:
+	CRC16_Slow() : CRCSlow<uint16>(0x8005, 0x0000, 0x0000, true) {}
+};
+
+class CRC32_Slow : public CRCSlow<uint32> {
+public:
+	CRC32_Slow() : CRCSlow<uint32>(0x04C11DB7, 0xFFFFFFFF, 0xFFFFFFFF, true) {}
+};
+
+} // End of namespace Common
+
+#endif