javascript - 在 Javascript 中添加或减去 64 位整数

Question

有没有简单的方法(希望是一个小函数，而不是库)在 JavaScript 中对 64 位整数进行加减？

示例 64 位整数:291270990346989568

背景:我正在使用具有 64 位推文 ID 的 Twitter API。我想从这些 ID 中添加或减去一个以操纵我从 Twitter 返回的结果。

Answer 1

以下代码执行您所描述的内容。

Splitting, adding or subtracting, then re-joining...

此代码同时具有递增和递减函数，以及具有一些边缘情况的测试函数。在拆分数字字符串并对它们进行数学运算时，您需要考虑“前导零”会发生什么情况，因此有一个填充函数。

谢谢贾斯汀提供 JSFiddle with this solution .

/*
 * Prepend zeros to expand a given string to given length
 *
 * @var {String} numStr Number
 * @var {Number} len    Length to pad out to
 *
 * @returns {String}
 */
function pad0 (numStr,len) {
  while (numStr.length < len) {
    numStr = "0" + numStr;
  }
  return numStr
}

/*
 * Decrement the given (64 bit) integer.
 *
 * @var {String} int64  Postive non-zero integer, as a string
 *
 * @returns {String}
 */
function decrInt64 (int64) {
  var result = "";
  var midpt = Math.floor(int64.length/2);
  var upper = int64.substring(0,midpt);
  var lower = int64.substring(midpt);
  var upperVal = new Number(upper);
  var lowerVal = new Number(lower);

  if (lowerVal == 0) {
    if (upperVal == 0) {
      // We don't support negative numbers
      result = "*ERROR*"
    }
    else {
      // borrow 1
      result = pad0((--upperVal).toString(),upper.length) +
               (new Number("1"+lower) - 1).toString();
    }
  }
  else {
    var newLower = (lowerVal - 1).toString();
    result = upper + pad0(newLower,lower.length);
  }
  alert(result);
}

/*
 * Increment the given (64 bit) integer.
 *
 * @var {String} int64  Postive, as a string
 *
 * @returns {String}
 */
function incrInt64 (int64) {
  var result = "";
  var midpt = Math.floor(int64.length/2);
  var upper = int64.substring(0,midpt);
  var lower = int64.substring(midpt);
  var upperVal = new Number(upper);
  var lowerVal = new Number(lower);

  var newLower = (++lowerVal).toString();
  // Did we overflow?
  if (lower.length < newLower.length) {
    // Yes, carry the 1
    result = (++upperVal).toString() + newLower.substring(1);
  }
  else {
    result = upper + pad0(newLower,lower.length);
  }
  alert(result);
}

// Test function
window.displaymessage= function ()
{
  decrInt64("291270990046989568");
  incrInt64("291270990046989568");
  decrInt64("000000000000000000");
  incrInt64("000000000000000000");
  decrInt64("000000001000000000");
  incrInt64("000000001000000000");
  decrInt64("099999999999999999");
  incrInt64("099999999999999999");
  decrInt64("999999999999999999");
  incrInt64("999999999999999999");
}