Question

以下代码是我尝试相当通用的javascript哈希代码实现。我计划将此代码与哈希表实现（例如jshashtable）一起使用，如果为键定义了hashCode（），则使用hashCode（）。我试图密切关注java的数字，字符串和数组的哈希代码实现。

问题：

此实施方面是否存在关于正确性的问题还是表现？
是否有任何预先存在的哈希实现执行相同（或大致相同）事情的代码？
除此之外 jshashtable，是否有其他利用的哈希表实现 hashCode（）和equals（）的方式与我应该考虑的方式相同吗？

注意：我知道下面的代码可以利用其他库，例如下划线和jquery，但我不希望我的实现有任何第三方代码。这并不是说我对自己可能依赖于jquery，下划线等的哈希代码库不感兴趣。

/**
* Computes a hash code for an object based on a given subset of its fields 
* @param obj any type
* @param keys an array of strings representing some subset of the keys in obj or undefined
* @returns {Number} a java-like hash code for obj based on the hash codes of a subset of its fields
*           specified in keys.
*/
function hashCode(obj, keys) {

   if (!isDefined(keys)) return typeHashCode(obj);

   var result = 1;
   for (var k = 0; k < keys.length; k++) {
      var key = keys[k];
      if (isDefined(obj[key]))
        result = multiplyBy31AndAdd(result, typeHashCode(obj[key]));
   }

   return result;
}

/**
 * @param obj
 * @returns {Number}
*/
function typeHashCode(obj) {
   var result = 1;
   if (isDefined(obj)) {
      if (typeof obj === 'string') 
         result  = multiplyBy31AndAdd(result, stringHashCode(obj));
      else if (typeof obj === 'number' && isFinite(obj)) 
         result  = multiplyBy31AndAdd(result, numberHashCode(obj));
      else if (typeof obj === 'object') {
         if (nonEmptyObject(obj)) {
            if (isDefined(obj[hashCode])) 
                result = multiplyBy31AndAdd(result, obj.hashCode());
            else {
                if (Array.isArray(obj)) 
                    result = multiplyBy31AndAdd(result, arrayHashCode(obj));
                else { 
                    //This is what jshashtable does. If there were an easy and agreed upon way
                    //of uniquely identifying objects in javascript, a better approach
                    //may be to use the object's id
                    result  = multiplyBy31AndAdd(result, stringHashCode(obj.toString()));
                }
            }
        }
      }
   }
   return result;
}

/**
 * Generates a hash code for a 64 bit floating point number, similar to java's hash 
 * code implementation. This does not handle NaN and Inf the same way as java. 
 * More info can be found at [1]
 * [1] http://stackoverflow.com/questions/2003493/javascript-float-from-to-bits
 * @param num a finite number as defined by isFinite()
 * @returns {Number}
*/
function numberHashCode(num) {
   var buf = new ArrayBuffer(8);
   (new Float64Array(buf))[0] = num;
   return (new Uint32Array(buf))[0] ^ (new Uint32Array(buf))[1];    
}

/**
 * Generates a hash code for a string, similar to java's hash code 
 * implementation. More info can be found at [1]
 * [1] http://stackoverflow.com/questions/7616461/generate-a-hash-from-string-in-javascript-jquery
 * @returns {Number}
 */
function stringHashCode(str) {
   var hash = 0;
   if (str.length === 0) return hash;
   for (var i = 0; i < str.length; i++) {
     var character  = str.charCodeAt(i);
     hash  = multiplyBy31AndAdd(hash, character);
   }
   return hash;
}

/**
 * @param array
 * @returns {Number} hash code for the array
*/
function arrayHashCode(array) {
   var result = 1;
   for (var i = 0; i < array.length; i++) {
     result = multiplyBy31AndAdd(result, typeHashCode(obj));
   }
   return result;
}

/**
 * Code taken from:
 * http://stackoverflow.com/questions/7616461/generate-a-hash-from-string-in-javascript-jquery
 * @param currentValue a number
 * @param toAdd a number
 * @returns {Number} the 32 bit integer representation of 31 * currentValue + toAdd
*/
function multiplyBy31AndAdd(currentValue, toAdd) {
   var rv = ((currentValue<<5)-currentValue)+toAdd;
   return rv & rv; //Convert to 32 bit integer
}


function isDefined(obj) {
   return !(obj === undefined || obj === null);
}

/**
 * Taken from http://stackoverflow.com/questions/4994201/is-object-empty
 * @param obj an object
 * @returns {Boolean} obj is {}
*/
function nonEmptyObject(obj) {
   return !(Object.keys(obj).length === 0);
}

javascript（类似java）哈希码实现

0 个答案: