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LEON
Asked:2021-11-06 07:07:04 +0800 CST2021-11-06 07:07:04 +0800 CST

将大整数转换为base64

  • 772

如何将大 int 转换为 base64（不是字符串而是数字）？

示例：215968764→DN9r_A

javascript

3 个回答

  1. Best Answer

    从示例来看，这是来自 32 位 Big-Endian 的 base64，因为它值得在标签中nodejs使用Buffer：

    function number2base64(n) {
    // тут стоит проверить, что n < 2^32
    const b = Buffer.alloc(4);
    b.writeUInt32BE(n);         // записываем число в буфер
    return b.toString('base64') // получаем base64 и преобразуем в base64url
        .slice(0, 6)            // убираем паддинг
        .replace(/\+/g, '-')    // '+' → '-'
        .replace(/\//g, '_');   // '/' → '_'
}

    实际上，这个数字的真正 base64 看起来像这样：DN9r/A==，但在示例中通常称为base64url

    • 8

  2. JavaScript 语言中有两个函数分别用于对 Base64 格式的数据进行编码和解码：

    • btoa()
    • atob()

    btoa()只接受一个字符串，但是你可以在那里传递一个数字，但atob()它总是会返回一个字符串。

    btoa(15) === btoa("15")

    资源

    • 0

  3. 资源

    const Base64 = {
  _keyStr: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",
  encode: function(input) {
    input = new String(input);
    var output = "";
    var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
    var i = 0;

    input = Base64._utf8_encode(input);

    while (i < input.length) {

      chr1 = input.charCodeAt(i++);
      chr2 = input.charCodeAt(i++);
      chr3 = input.charCodeAt(i++);

      enc1 = chr1 >> 2;
      enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
      enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
      enc4 = chr3 & 63;

      if (isNaN(chr2)) {
        enc3 = enc4 = 64;
      } else if (isNaN(chr3)) {
        enc4 = 64;
      }

      output = output +
        this._keyStr.charAt(enc1) + this._keyStr.charAt(enc2) +
        this._keyStr.charAt(enc3) + this._keyStr.charAt(enc4);

    }

    return output;
  },
  decode: function(input) {
    var output = "";
    var chr1, chr2, chr3;
    var enc1, enc2, enc3, enc4;
    var i = 0;

    input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");

    while (i < input.length) {

      enc1 = this._keyStr.indexOf(input.charAt(i++));
      enc2 = this._keyStr.indexOf(input.charAt(i++));
      enc3 = this._keyStr.indexOf(input.charAt(i++));
      enc4 = this._keyStr.indexOf(input.charAt(i++));

      chr1 = (enc1 << 2) | (enc2 >> 4);
      chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
      chr3 = ((enc3 & 3) << 6) | enc4;

      output = output + String.fromCharCode(chr1);

      if (enc3 != 64) {
        output = output + String.fromCharCode(chr2);
      }
      if (enc4 != 64) {
        output = output + String.fromCharCode(chr3);
      }

    }

    output = Base64._utf8_decode(output);
    
    if (isAN(+output)) {
      output = +output;
    }

    return output;

  },
  _utf8_encode: function(string) {
    string = string.replace(/\r\n/g, "\n");
    var utftext = "";

    for (var n = 0; n < string.length; n++) {

      var c = string.charCodeAt(n);

      if (c < 128) {
        utftext += String.fromCharCode(c);
      } else if ((c > 127) && (c < 2048)) {
        utftext += String.fromCharCode((c >> 6) | 192);
        utftext += String.fromCharCode((c & 63) | 128);
      } else {
        utftext += String.fromCharCode((c >> 12) | 224);
        utftext += String.fromCharCode(((c >> 6) & 63) | 128);
        utftext += String.fromCharCode((c & 63) | 128);
      }

    }

    return utftext;
  },
  _utf8_decode: function(utftext) {
    var string = "";
    var i = 0;
    var c = c1 = c2 = 0;

    while (i < utftext.length) {

      c = utftext.charCodeAt(i);

      if (c < 128) {
        string += String.fromCharCode(c);
        i++;
      } else if ((c > 191) && (c < 224)) {
        c2 = utftext.charCodeAt(i + 1);
        string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
        i += 2;
      } else {
        c2 = utftext.charCodeAt(i + 1);
        c3 = utftext.charCodeAt(i + 2);
        string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
        i += 3;
      }

    }

    return string;
  }

}

function isAN(value) {
  return (value instanceof Number||typeof value === 'number') && !isNaN(value);
}

const num = 123;

const encodedString = Base64.encode(num);
console.log(encodedString);

const decodedString = Base64.decode(encodedString);
console.log(decodedString, typeof decodedString);

    • 0

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