Base64 编码介绍、Base64编码转换原理、算法

深藏阁楼爱情的钟 2022-07-11 06:57 251阅读 0赞

Base64编码，是我们程序开发中经常使用到的编码方法。它是一种基于用64个可打印字符来表示二进制数据的表示方法。它通常用作存储、传输一些二进制数据编码方法！也是MIME（多用途互联网邮件扩展，主要用作电子邮件标准）中一种可打印字符表示二进制数据的常见编码方法！它其实只是定义用可打印字符传输内容一种方法，并不会产生新的字符集！有时候，我们学习转换的思路后，我们其实也可以结合自己的实际需要，构造一些自己接口定义编码方式。好了，我们一起看看，它的转换思路吧！

Base64实现转换原理

它是用64个可打印字符表示二进制所有数据方法。由于2的6次方等于64，所以可以用每6个位元为一个单元，对应某个可打印字符。我们知道三个字节有24个位元，就可以刚好对应于4个Base64单元，即3个字节需要用4个Base64的可打印字符来表示。在Base64中的可打印字符包括字母A-Z、a-z、数字0-9 ，这样共有62个字符，此外两个可打印符号在不同的系统中一般有所不同。但是，我们经常所说的Base64另外2个字符是：“+/”。这64个字符，所对应表如下。

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>    <th style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> 编号</th> 
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>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> A</td> 
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>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> Q</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 32</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> g</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 48</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> w</td> 
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>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> B</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 17</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> R</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 33</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> h</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 49</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> x</td> 
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>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 2</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> C</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 18</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> S</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 34</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> i</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 50</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> y</td> 
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>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 3</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> D</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 19</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> T</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 35</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> j</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 51</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> z</td> 
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>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 4</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> E</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 20</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> U</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 36</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> k</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 52</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
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>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 5</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> F</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 21</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> V</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 37</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> l</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 53</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
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>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 6</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> G</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 22</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> W</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 38</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> m</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 54</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 2</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 7</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> H</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 23</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> X</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 39</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> n</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 55</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 3</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 8</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> I</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 24</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> Y</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 40</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> o</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 56</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 4</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 9</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> J</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 25</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> Z</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 41</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> p</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 57</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 5</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 10</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> K</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 26</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> a</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 42</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> q</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 58</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 6</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 11</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> L</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 27</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> b</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 43</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> r</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 59</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 7</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 12</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> M</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 28</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> c</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 44</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> s</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 60</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 8</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 13</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> N</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 29</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> d</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 45</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> t</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 61</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 9</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 14</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> O</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 30</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> e</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 46</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> u</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 62</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> +</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 15</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> P</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 31</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> f</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 47</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> v</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 63</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> /</td> 
>   </tr> 
>  </tbody> 
> </table>

Base64编码转换算法、转换原理

> 转换的时候，将三个byte的数据，先后放入一个24bit的缓冲区中，先来的byte占高位。数据不足3byte的话，于缓冲区中剩下的bit用0补足。然后，每次取出6个bit，按照其值选择`ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/`中的字符作为编码后的输出。不断进行，直到全部输入数据转换完成。
> 
> 如果最后剩下两个输入数据，在编码结果后加1个“=”；如果最后剩下一个输入数据，编码结果后加2个“=”；如果没有剩下任何数据，就什么都不要加，这样才可以保证资料还原的正确性。
> 
> 编码后的数据比原始数据略长，为原来的4/3。无论什么样的字符都会全部被编码，因此不像[Quoted-printable][] 编码，还保留部分可打印字符。所以，它的可读性不如[Quoted-printable][]编码！
> 
> <table style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> 
>  <tbody style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <th style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> 文本</th> 
>    <td colspan="8" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">M</span></td> 
>    <td colspan="8" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">a</span></td> 
>    <td colspan="8" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">n</span></td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <th style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> ASCII编码</th> 
>    <td colspan="8" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 77</td> 
>    <td colspan="8" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 97</td> 
>    <td colspan="8" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 110</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <th style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> 二进制位</th> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <th style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> 索引</th> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 19</td> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 22</td> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 5</td> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 46</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <th style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> Base64编码</th> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">T</span></td> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">W</span></td> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">F</span></td> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">u</span></td> 
>   </tr> 
>  </tbody> 
> </table>
> 
> M的Ascii码是77,前六位对应值为19，对应base64字符是T，如此类推。其它字符编码就可以自动转换得到！我们看看另外不是刚好是3个字节的情况！
> 
> <table style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> 
>  <tbody style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <th style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> 文本（1 Byte）</th> 
>    <td colspan="8" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">A</span></td> 
>    <td colspan="8" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td colspan="8" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <th style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> 二进制位</th> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <th style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> 二进制位（补0）</th> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">0</span></td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">0</span></td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">0</span></td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">0</span></td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <th style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> Base64编码</th> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">Q</span></td> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">Q</span></td> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">=</span></td> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">=</span></td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <th style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> 文本（2 Byte）</th> 
>    <td colspan="8" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">B</span></td> 
>    <td colspan="8" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">C</span></td> 
>    <td colspan="8" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <th style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> 二进制位</th> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> x</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> x</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> x</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> x</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> x</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> x</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <th style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> 二进制位（补0）</th> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 0</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> 1</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">0</span></td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">0</span></td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> x</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> x</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> x</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> x</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> x</td> 
>    <td style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> x</td> 
>   </tr> 
>   <tr style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent"> 
>    <th style="margin:0px; padding:0px; border:1px solid black; outline:0px; font-size:16px; vertical-align:baseline; background:transparent"> Base64编码</th> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">Q</span></td> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">k</span></td> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> <span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">M</span></td> 
>    <td colspan="6" align="middle" style="margin:0px; padding:4px; border:1px solid rgb(102,102,102); outline:0px; font-size:16px; vertical-align:baseline; text-indent:0em"> &nbsp;<span style="margin:0px; padding:0px; border:0px; outline:0px; vertical-align:baseline; background:transparent">=</span></td> 
>   </tr> 
>  </tbody> 
> </table>

Base64转换代码实现

既然知道了方法，那么我们如果要自己写个简单转换，好像也是很容易的！下面，我写下我做转换php代码！

>     /**
>      *base64编码方法、本方法只是做base64转换过程代码举例说明，通过该例子可以任意改造不同语言版
>      *@author 程默
>      *@copyright http://blog.chacuo.net
>      *@param $src 原字符串
>      *@return string base64字符串*
>      */
>     function c_base64_encode($src)
>     {
>     	static $base="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
>     	
>     	将原始的3个字节转换为4个字节
>     	$slen=strlen($src);
>     	$smod = ($slen%3);
>     	$snum = floor($slen/3);
>     	
>     	
>     	$desc = array();
>     	
>     	for($i=0;$i<$snum;$i++)
>     	{
>     		读取3个字节
>     		$_arr = array_map('ord',str_split(substr($src,$i*3,3)));
>     		
>     		///计算每一个base64值
>     		$_dec0= $_arr[0]>>2;
>     		$_dec1= (($_arr[0]&3)<<4)|($_arr[1]>>4);
>     		$_dec2= (($_arr[1]&0xF)<<2)|($_arr[2]>>6);	
>     		$_dec3= $_arr[2]&63;
>     
>     		$desc = array_merge($desc,array($base[$_dec0],$base[$_dec1],$base[$_dec2],$base[$_dec3]));
>     	}
>     	
>     	if($smod==0) return implode('',$desc);
>     	
>     	///计算非3倍数字节
>     	$_arr = array_map('ord',str_split(substr($src,$snum*3,3)));
>     	$_dec0= $_arr[0]>>2;
>     	///只有一个字节
>     	if(!isset($_arr[1]))
>     	{
>     		$_dec1= (($_arr[0]&3)<<4);
>     		$_dec2=$_dec3="=";
>     	}
>     	else 
>     	{
>     		///2个字节
>     		$_dec1= (($_arr[0]&3)<<4)|($_arr[1]>>4);
>     		$_dec2= $base[($_arr[1]&7)<<2];
>     		$_dec3="=";
>     	}
>     	$desc = array_merge($desc,array($base[$_dec0],$base[$_dec1],$_dec2,$_dec3));
>     	return implode('',$desc);
>     }

好了，通过这个例子，我想base64编码转换原理、算法有些了解了吧！它转换过程很简单，只需要做个映射表，然后将原先做一些移位运算就可以完成！我们通过该例子，是不是可以做个自己的base32这类的编码呢！欢迎朋友们交流！

[Quoted-printable]: http://blog.chacuo.net/494.html