C++实现的Base64编码

#include "RLib.h"
//////////////////////////////////////////////////////////////////////////
const static unsigned int MAX_LINE_LENGTH = 76;

const static char BASE64_ALPHABET [64] = 
	{
	'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', //   0 -   9
	'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', //  10 -  19
	'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', //  20 -  29
	'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', //  30 -  39
	'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', //  40 -  49
	'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', //  50 -  59
	'8', '9', '+', '/'								  //  60 -  63
	};

const static char BASE64_DEALPHABET [128] = 
	{
	 0,  0,  0,  0,  0,  0,  0,  0,  0,  0, //   0 -   9
	 0,  0,  0,  0,  0,  0,  0,  0,  0,  0, //  10 -  19
	 0,  0,  0,  0,  0,  0,  0,  0,  0,  0, //  20 -  29
	 0,  0,  0,  0,  0,  0,  0,  0,  0,  0, //  30 -  39
	 0,  0,  0, 62,  0,  0,  0, 63, 52, 53, //  40 -  49
	54, 55, 56, 57, 58, 59, 60, 61,  0,  0, //  50 -  59
	 0, 61,  0,  0,  0,  0,  1,  2,  3,  4, //  60 -  69
	 5,  6,  7,  8,  9, 10, 11, 12, 13, 14, //  70 -  79
	15, 16, 17, 18, 19, 20, 21, 22, 23, 24, //  80 -  89
	25,  0,  0,  0,  0,  0,  0, 26, 27, 28, //  90 -  99
	29, 30, 31, 32, 33, 34, 35, 36, 37, 38, // 100 - 109
	39, 40, 41, 42, 43, 44, 45, 46, 47, 48, // 110 - 119
	49, 50, 51,  0,  0,  0,  0,  0			// 120 - 127
	};

enum
	{
	UNABLE_TO_OPEN_INPUT_FILE,
	UNABLE_TO_OPEN_OUTPUT_FILE,
	UNABLE_TO_CREATE_OUTPUTBUFFER
	};

class export Base64
{
private:
	UINT CalcRecquiredEncodeOutBufSize(UINT  p_InputByteCount);
	UINT CalcRecquiredDecodeOutBufSize(char *p_pInputBufferString);

	void EncodeByteTriple(char *p_pInputBuffer, UINT InputCharacters, char *p_pOutputBuffer);
	UINT DecodeByteQuartet(char *p_pInputBuffer, char *p_pOutputBuffer);
public:
	void			EncodeBuffer (char *p_pInputBuffer, UINT p_InputBufferLength, char *p_pOutputBufferString);
	unsigned int	DecodeBuffer (char *p_pInputBufferString, char *p_pOutputBuffer);
};

#include "Lib_Text.h"
//////////////////////////////////////////////////////////////////////////
unsigned int Base64::CalcRecquiredEncodeOutBufSize (unsigned int p_InputByteCount)
	{
	div_t result = div (p_InputByteCount, 3);

	unsigned int RecquiredBytes = 0;
	if (result.rem == 0)
		{
		// Number of encoded characters
		RecquiredBytes = result.quot * 4;

		// CRLF -> "\r\n" each 76 characters
		result = div (RecquiredBytes, 76);
		RecquiredBytes += result.quot * 2;

		// Terminating null for the Encoded String
		RecquiredBytes += 1;

		return RecquiredBytes;
		}
	else
		{
		// Number of encoded characters
		RecquiredBytes = result.quot * 4 + 4;

		// CRLF -> "\r\n" each 76 characters
		result = div (RecquiredBytes, 76);
		RecquiredBytes += result.quot * 2;

		// Terminating null for the Encoded String
		RecquiredBytes += 1;

		return RecquiredBytes;
		}
	}

unsigned int Base64::CalcRecquiredDecodeOutBufSize (char* p_pInputBufferString)
	{
	unsigned int BufferLength = strlen (p_pInputBufferString);

	div_t result = div (BufferLength, 4);

	if (p_pInputBufferString [BufferLength - 1] != '=')
		{
		return result.quot * 3;
		}
	else
		{
		if (p_pInputBufferString [BufferLength - 2] == '=')
			{
			return result.quot * 3 - 2;
			}
		else
			{
			return result.quot * 3 - 1;
			}
		}
	}

void Base64::EncodeByteTriple  (char* p_pInputBuffer, unsigned int InputCharacters, char* p_pOutputBuffer)
	{
	unsigned int mask = 0xfc000000;
	unsigned int buffer = 0;


	char* temp = (char*) &buffer;
	temp [3] = p_pInputBuffer [0];
	if (InputCharacters > 1)
		temp [2] = p_pInputBuffer [1];
	if (InputCharacters > 2)
		temp [1] = p_pInputBuffer [2];

	switch (InputCharacters)
		{
		case 3:
			{
			p_pOutputBuffer [0] = BASE64_ALPHABET [(buffer & mask) >> 26];
			buffer = buffer << 6;
			p_pOutputBuffer [1] = BASE64_ALPHABET [(buffer & mask) >> 26];
			buffer = buffer << 6;
			p_pOutputBuffer [2] = BASE64_ALPHABET [(buffer & mask) >> 26];
			buffer = buffer << 6;
			p_pOutputBuffer [3] = BASE64_ALPHABET [(buffer & mask) >> 26];
			break;
			}
		case 2:
			{
			p_pOutputBuffer [0] = BASE64_ALPHABET [(buffer & mask) >> 26];
			buffer = buffer << 6;
			p_pOutputBuffer [1] = BASE64_ALPHABET [(buffer & mask) >> 26];
			buffer = buffer << 6;
			p_pOutputBuffer [2] = BASE64_ALPHABET [(buffer & mask) >> 26];
			p_pOutputBuffer [3] = '=';
			break;
			}
		case 1:
			{
			p_pOutputBuffer [0] = BASE64_ALPHABET [(buffer & mask) >> 26];
			buffer = buffer << 6;
			p_pOutputBuffer [1] = BASE64_ALPHABET [(buffer & mask) >> 26];
			p_pOutputBuffer [2] = '=';
			p_pOutputBuffer [3] = '=';
			break;
			}
		}
	}

unsigned int Base64::DecodeByteQuartet (char* p_pInputBuffer, char* p_pOutputBuffer)
	{
	unsigned int buffer = 0;

	if (p_pInputBuffer[3] == '=')
		{
		if (p_pInputBuffer[2] == '=')
			{
			buffer = (buffer | BASE64_DEALPHABET [p_pInputBuffer[0]]) << 6;
			buffer = (buffer | BASE64_DEALPHABET [p_pInputBuffer[1]]) << 6;
			buffer = buffer << 14;

			char* temp = (char*) &buffer;
			p_pOutputBuffer [0] = temp [3];
			
			return 1;
			}
		else
			{
			buffer = (buffer | BASE64_DEALPHABET [p_pInputBuffer[0]]) << 6;
			buffer = (buffer | BASE64_DEALPHABET [p_pInputBuffer[1]]) << 6;
			buffer = (buffer | BASE64_DEALPHABET [p_pInputBuffer[2]]) << 6;
			buffer = buffer << 8;

			char* temp = (char*) &buffer;
			p_pOutputBuffer [0] = temp [3];
			p_pOutputBuffer [1] = temp [2];
			
			return 2;
			}
		}
	else
		{
		buffer = (buffer | BASE64_DEALPHABET [p_pInputBuffer[0]]) << 6;
		buffer = (buffer | BASE64_DEALPHABET [p_pInputBuffer[1]]) << 6;
		buffer = (buffer | BASE64_DEALPHABET [p_pInputBuffer[2]]) << 6;
		buffer = (buffer | BASE64_DEALPHABET [p_pInputBuffer[3]]) << 6; 
		buffer = buffer << 2;

		char* temp = (char*) &buffer;
		p_pOutputBuffer [0] = temp [3];
		p_pOutputBuffer [1] = temp [2];
		p_pOutputBuffer [2] = temp [1];

		return 3;
		}

	return -1;
	}

void Base64::EncodeBuffer (char* p_pInputBuffer, unsigned int p_InputBufferLength, char* p_pOutputBufferString)
	{
	unsigned int FinishedByteQuartetsPerLine = 0;
	unsigned int InputBufferIndex  = 0;
	unsigned int OutputBufferIndex = 0;

	memset (p_pOutputBufferString, 0, CalcRecquiredEncodeOutBufSize (p_InputBufferLength));

	while (InputBufferIndex < p_InputBufferLength)
		{
		if (p_InputBufferLength - InputBufferIndex <= 2)
			{
			FinishedByteQuartetsPerLine ++;
			EncodeByteTriple (p_pInputBuffer + InputBufferIndex, p_InputBufferLength - InputBufferIndex, p_pOutputBufferString + OutputBufferIndex);
			break;
			}
		else
			{
			FinishedByteQuartetsPerLine++;
			EncodeByteTriple (p_pInputBuffer + InputBufferIndex, 3, p_pOutputBufferString + OutputBufferIndex);
			InputBufferIndex  += 3;
			OutputBufferIndex += 4;
			}

		if (FinishedByteQuartetsPerLine == 19)
			{
			p_pOutputBufferString [OutputBufferIndex  ] = '\r';
			p_pOutputBufferString [OutputBufferIndex+1] = '\n';
			p_pOutputBufferString += 2;
			FinishedByteQuartetsPerLine = 0;
			}
		}
	}

unsigned int Base64::DecodeBuffer (char* p_pInputBufferString, char* p_pOutputBuffer)
	{
	unsigned int InputBufferIndex  = 0;
	unsigned int OutputBufferIndex = 0;
	unsigned int InputBufferLength = strlen (p_pInputBufferString);

	char ByteQuartet [4];

	while (InputBufferIndex < InputBufferLength)
		{
		for (int i = 0; i < 4; i++)
			{
			ByteQuartet [i] = p_pInputBufferString [InputBufferIndex];

			// Ignore all characters except the ones in BASE64_ALPHABET
			if ((ByteQuartet [i] >= 48 && ByteQuartet [i] <=  57) ||
				(ByteQuartet [i] >= 65 && ByteQuartet [i] <=  90) ||
				(ByteQuartet [i] >= 97 && ByteQuartet [i] <= 122) ||
				 ByteQuartet [i] == '+' || ByteQuartet [i] == '/' || ByteQuartet [i] == '=')
				{
				}
			else
				{
				// Invalid character
				i--;
				}

			InputBufferIndex++;
			}

		OutputBufferIndex += DecodeByteQuartet (ByteQuartet, p_pOutputBuffer + OutputBufferIndex);
		}

	// OutputBufferIndex gives us the next position of the next decoded character
	// inside our output buffer and thus represents the number of decoded characters
	// in our buffer.
	return OutputBufferIndex;
	}