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Editor/Util/crc32.cpp

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+#include "stdafx.h"
+#include "crc32.h"
+
+Crc32Gen::Crc32Gen()
+{
+	init_CRC32_Table();
+}
+
+// Call this function only once to initialize the CRC table.
+void Crc32Gen::init_CRC32_Table()
+{
+	// This is the official polynomial used by CRC-32
+	// in PKZip, WinZip and Ethernet.
+	unsigned int ulPolynomial = 0x04c11db7;
+	
+	// 256 values representing ASCII character codes.
+	for(int i = 0; i <= 0xFF; i++)
+	{
+		crc32_table[i] = reflect(i, 8) << 24;
+		for (int j = 0; j < 8; j++)
+			crc32_table[i] = (crc32_table[i] << 1) ^ (crc32_table[i] & (1 << 31) ? ulPolynomial : 0);
+		crc32_table[i] = reflect(crc32_table[i], 32);
+	}
+}
+
+unsigned int Crc32Gen::reflect(unsigned int ref, char ch)
+{// Used only by Init_CRC32_Table().
+	unsigned int value = 0;
+	
+	// Swap bit 0 for bit 7
+	// bit 1 for bit 6, etc.
+	for(int i = 1; i < (ch + 1); i++)
+	{
+		if(ref & 1)
+			value |= 1 << (ch - i);
+		ref >>= 1;
+	}
+	return value;
+}
+
+unsigned int Crc32Gen::get_CRC32( const char *data, int size, unsigned int ulCRC )
+{// Pass a text string to this function and it will return the CRC.
+	
+	// Once the lookup table has been filled in by the two functions above,
+	// this function creates all CRCs using only the lookup table.
+	
+	// Be sure to use unsigned variables, because negative values introduce high bits where zero bits are required.
+	
+	// Start out with all bits set high.
+	int len; 
+	unsigned char* buffer;
+	
+	// Get the length. 
+	len = size; 
+	
+  // Save the text in the buffer. 
+	buffer = (unsigned char*)data; 
+	// Perform the algorithm on each character in the string, using the lookup table values. 
+	
+	while(len--) 
+		ulCRC = (ulCRC >> 8) ^ crc32_table[(ulCRC & 0xFF) ^ *buffer++]; 
+	// Exclusive OR the result with the beginning value. 
+	return ulCRC ^ 0xffffffff; 
+} 
+
+unsigned int Crc32Gen::GetCRC32( const char *text )
+{
+	int len = strlen(text);
+	return GetCRC32( text,len,0xffffffff );
+}
+
+unsigned int Crc32Gen::GetCRC32( const char *data, int size, unsigned int ulCRC )
+{
+	static Crc32Gen stdCrc32Generator;
+	return stdCrc32Generator.get_CRC32( data,size,ulCRC );
+}