base64decoder.cs

base64编码/解吗程序。。 下载后按个人的需要修改

using System;

namespace TestBase64
{
	/// <summary>
	/// Summary description for Base64Decoder.
	/// </summary>
	public class Base64Decoder
	{
		char[] source;
		int length, length2, length3;
		int blockCount;
		int paddingCount;
		public Base64Decoder(char[] input)
		{
			int temp=0;
			source=input;
			length=input.Length;

			//find how many padding are there
			for (int x=0;x<2;x++)
			{
				if(input[length-x-1]=='=')
					temp++;
			}
			paddingCount=temp;
			//calculate the blockCount;
			//assuming all whitespace and carriage returns/newline were removed.
			blockCount=length/4;
			length2=blockCount*3;
		}

		public byte[] GetDecoded()
		{
			byte[] buffer=new byte[length];//first conversion result
			byte[] buffer2=new byte[length2];//decoded array with padding

			for(int x=0;x<length;x++)
			{
				buffer[x]=char2sixbit(source[x]);
			}

			byte b, b1,b2,b3;
			byte temp1, temp2, temp3, temp4;

			for(int x=0;x<blockCount;x++)
			{
				temp1=buffer[x*4];
				temp2=buffer[x*4+1];
				temp3=buffer[x*4+2];
				temp4=buffer[x*4+3];				

				b=(byte)(temp1<<2);
				b1=(byte)((temp2 & 48)>>4);
				b1+=b;

				b=(byte)((temp2 & 15)<<4);
				b2=(byte)((temp3 & 60)>>2);
				b2+=b;

				b=(byte)((temp3 & 3)<<6);
				b3=temp4;
				b3+=b;

				buffer2[x*3]=b1;
				buffer2[x*3+1]=b2;
				buffer2[x*3+2]=b3;
			}
			//remove paddings
			length3=length2-paddingCount;
			byte[] result=new byte[length3];

			for(int x=0;x<length3;x++)
			{
				result[x]=buffer2[x];
			}

			return result;
		}

		private byte char2sixbit(char c)
		{
			char[] lookupTable=new char[64]
					{	'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',
						'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',
						'0','1','2','3','4','5','6','7','8','9','+','/'};
			if(c=='=')
				return 0;
			else
			{
				for (int x=0;x<64;x++)
				{
					if (lookupTable[x]==c)
						return (byte)x;
				}
				//should not reach here
				return 0;
			}

		}

	}
}