/Code/CryEngine/CryCommon/crc32.h

////////////////////////////////////////////////////////////////////////////

//

//  Crytek Engine Source File.

//  Copyright (C), Crytek Studios, 2002.

// -------------------------------------------------------------------------

//  File name:   crc32.h

//  Version:     v1.00

//  Created:     31/10/2002 by Timur.

//  Compilers:   Visual Studio.NET

//  Description: 

// -------------------------------------------------------------------------

//  History:

//

////////////////////////////////////////////////////////////////////////////



#ifndef __crc32_h__

#define __crc32_h__



#if _MSC_VER > 1000

#pragma once

#endif



class Crc32Gen 

{

public:

	Crc32Gen();



  void Init() {

    if (!m_bInited)

    {

      m_bInited = true;

      init_CRC32_Table();

    }

  }



	//! Creates a CRC from a text string 

	unsigned int GetCRC32( const char *text ) const;

	unsigned int GetCRC32( const char *data,int size,unsigned int ulCRC ) const;



	unsigned int GetCRC32Lowercase( const char *text ) const;

	unsigned int GetCRC32Lowercase( const char *data,int size,unsigned int ulCRC ) const;



protected:

	unsigned int crc32_table[256];  //!< Lookup table array

  bool m_bInited;



	void init_CRC32_Table();  //!< Builds lookup table array 

	unsigned int reflect( unsigned int ref, char ch); //!< Reflects CRC bits in the lookup table 

	unsigned int get_CRC32( const char *data,int size,unsigned int ulCRC ) const;

	unsigned int get_CRC32Lowercase( const char *data,int size,unsigned int ulCRC ) const;



} _ALIGN(128);



inline unsigned int Crc32Gen::GetCRC32( const char *text ) const

{

	int len = strlen(text);

	return GetCRC32( text,len,0xffffffff );

}



inline unsigned int Crc32Gen::GetCRC32( const char *data, int size, unsigned int ulCRC ) const

{

	return get_CRC32( data,size,ulCRC );

}



inline unsigned int Crc32Gen::GetCRC32Lowercase( const char *text ) const

{

	int len = strlen(text);

	return GetCRC32Lowercase( text,len,0xffffffff );

}



inline unsigned int Crc32Gen::GetCRC32Lowercase( const char *data, int size, unsigned int ulCRC ) const

{

	return get_CRC32Lowercase( data,size,ulCRC );

}



#define _ascii_tolower(c)     ( (((c) >= L'A') && ((c) <= L'Z')) ? ((c) - L'A' + L'a') : (c) )



inline unsigned int Crc32Gen::get_CRC32Lowercase( const char *data,int size,unsigned int ulCRC ) const

{	

	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--) 

  {

    unsigned char c = *buffer++;

	  ulCRC = (ulCRC >> 8) ^ crc32_table[(ulCRC & 0xFF) ^ _ascii_tolower(c)]; 

  }

	// Exclusive OR the result with the beginning value. 

	return ulCRC ^ 0xffffffff; 

} 



inline unsigned int Crc32Gen::get_CRC32( const char *data, int size, unsigned int ulCRC ) const

{

	// 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; 

} 



inline Crc32Gen::Crc32Gen()

{

	m_bInited = false;

  Init();

}



inline 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;

}





// Call this function only once to initialize the CRC table.

inline 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] & (1U << 31) ? ulPolynomial : 0);

		crc32_table[i] = reflect(crc32_table[i], 32);

	}

}





#endif // __crc32_h__