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用js编解码base64  

2015-01-14 03:32:54|  分类: 默认分类 |  标签: |举报 |字号 订阅

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用js编解码base64

编码规则
Base64编码的思想是是采用64个基本的ASCII码字符对数据进行重新编码。它将需要编码的数据拆分成字节数组。以3个字节为一组。按顺序排列24 位数据,再把这24位数据分成4组,即每组6位。再在每组的的最高位前补两个0凑足一个字节。这样就把一个3字节为一组的数据重新编码成了4个字节。当所要编码的数据的字节数不是3的整倍数,也就是说在分组时最后一组不够3个字节。这时在最后一组填充1到2个0字节。并在最后编码完成后在结尾添加1到2个 “=”。

实现的代码:

   1:  //下面是64个基本的编码
   2:  var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
   3:  var base64DecodeChars = new Array(
   4:      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
   5:      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
   6:      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
   7:      52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
   8:      -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
   9:      15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
  10:      -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
  11:      41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1);
  12:  //编码的方法
  13:  function base64encode(str) {
  14:      var out, i, len;
  15:      var c1, c2, c3;
  16:      len = str.length;
  17:      i = 0;
  18:      out = "";
  19:      while(i < len) {
  20:      c1 = str.charCodeAt(i++) & 0xff;
  21:      if(i == len)
  22:      {
  23:          out += base64EncodeChars.charAt(c1 >> 2);
  24:          out += base64EncodeChars.charAt((c1 & 0x3) << 4);
  25:          out += "==";
  26:          break;
  27:      }
  28:      c2 = str.charCodeAt(i++);
  29:      if(i == len)
  30:      {
  31:          out += base64EncodeChars.charAt(c1 >> 2);
  32:          out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));
  33:          out += base64EncodeChars.charAt((c2 & 0xF) << 2);
  34:          out += "=";
  35:          break;
  36:      }
  37:      c3 = str.charCodeAt(i++);
  38:      out += base64EncodeChars.charAt(c1 >> 2);
  39:      out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));
  40:      out += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >>6));
  41:      out += base64EncodeChars.charAt(c3 & 0x3F);
  42:      }
  43:      return out;
  44:  }
  45:  //解码的方法
  46:  function base64decode(str) {
  47:      var c1, c2, c3, c4;
  48:      var i, len, out;
  49:      len = str.length;
  50:      i = 0;
  51:      out = "";
  52:      while(i < len) {
  53:      
  54:      do {
  55:          c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
  56:      } while(i < len && c1 == -1);
  57:      if(c1 == -1)
  58:          break;
  59:      
  60:      do {
  61:          c2 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
  62:      } while(i < len && c2 == -1);
  63:      if(c2 == -1)
  64:          break;
  65:      out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));
  66:      
  67:      do {
  68:          c3 = str.charCodeAt(i++) & 0xff;
  69:          if(c3 == 61)
  70:          return out;
  71:          c3 = base64DecodeChars[c3];
  72:      } while(i < len && c3 == -1);
  73:      if(c3 == -1)
  74:          break;
  75:      out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));
  76:      
  77:      do {
  78:          c4 = str.charCodeAt(i++) & 0xff;
  79:          if(c4 == 61)
  80:          return out;
  81:          c4 = base64DecodeChars[c4];
  82:      } while(i < len && c4 == -1);
  83:      if(c4 == -1)
  84:          break;
  85:      out += String.fromCharCode(((c3 & 0x03) << 6) | c4);
  86:      }
  87:      return out;
  88:  }
  89:  function utf16to8(str) {
  90:      var out, i, len, c;
  91:      out = "";
  92:      len = str.length;
  93:      for(i = 0; i < len; i++) {
  94:      c = str.charCodeAt(i);
  95:      if ((c >= 0x0001) && (c <= 0x007F)) {
  96:          out += str.charAt(i);
  97:      } else if (c > 0x07FF) {
  98:          out += String.fromCharCode(0xE0 | ((c >> 12) & 0x0F));
  99:          out += String.fromCharCode(0x80 | ((c >>  6) & 0x3F));
 100:          out += String.fromCharCode(0x80 | ((c >>  0) & 0x3F));
 101:      } else {
 102:          out += String.fromCharCode(0xC0 | ((c >>  6) & 0x1F));
 103:          out += String.fromCharCode(0x80 | ((c >>  0) & 0x3F));
 104:      }
 105:      }
 106:      return out;
 107:  }
 108:  function utf8to16(str) {
 109:      var out, i, len, c;
 110:      var char2, char3;
 111:      out = "";
 112:      len = str.length;
 113:      i = 0;
 114:      while(i < len) {
 115:      c = str.charCodeAt(i++);
 116:      switch(c >> 4)
 117:      { 
 118:        case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
 119:          // 0xxxxxxx
 120:          out += str.charAt(i-1);
 121:          break;
 122:        case 12: case 13:
 123:          // 110x xxxx   10xx xxxx
 124:          char2 = str.charCodeAt(i++);
 125:          out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F));
 126:          break;
 127:        case 14:
 128:          // 1110 xxxx  10xx xxxx  10xx xxxx
 129:          char2 = str.charCodeAt(i++);
 130:          char3 = str.charCodeAt(i++);
 131:          out += String.fromCharCode(((c & 0x0F) << 12) |
 132:                         ((char2 & 0x3F) << 6) |
 133:                         ((char3 & 0x3F) << 0));
 134:          break;
 135:      }
 136:      }
 137:      return out;
 138:  }
?
调用:
?
   1:  //编码
   2:  value = base64encode(utf16to8(src))
   3:? 
   4:  //解码
   5:  value = utf8to16(base64decode(src))
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