js 处理浮点数问题

浮点数参数原因： （进制的换算导致了精度不准）
网上有个人举了个例子：你用十进制去想，0.7 是一个能准确表示的小数，而二进制却是循环小数。反过来想，就好像在十进制中 0.2 是一个很准确的数字，但在二进制中却是循环小数0.10110。除非用有理数表示，这些数字不能精确地用有限位的二进制表示，产生误差，0.7+0.1计算的结果也是有误差。把有误差的结果显示时，转换成十进位显示的算法发现该值与 0.8 相比，较接近 0.7999999999999999
浮点数原因

function NumberUtil(obj) {    return this;};NumberUtil.fn=NumberUtil.prototype;/** * 提供实例对外 */var NumUtil = new NumberUtil();window.NumUtil=NumUtil;/** * 加 * @param {Object} arg1 * @param {Object} arg2 */NumberUtil.fn.add=function(arg1,arg2){         var r1,r2,m;         try{r1=arg1.toString().split(".")[1].length}catch(e){r1=0}         try{r2=arg2.toString().split(".")[1].length}catch(e){r2=0}         m=Math.pow(10,Math.max(r1,r2));         return (arg1*m+arg2*m)/m;    }    /** * 减 * @param {Object} arg1 * @param {Object} arg2 */NumberUtil.fn.sub=function(arg1,arg2){        var r1,r2,m,n;        try{r1=arg1.toString().split(".")[1].length}catch(e){r1=0}        try{r2=arg2.toString().split(".")[1].length}catch(e){r2=0}        m=Math.pow(10,Math.max(r1,r2));        //动态控制精度长度        n=(r1>=r2)?r1:r2;        return ((arg1*m-arg2*m)/m).toFixed(n);}    /** * 乘 * @param {Object} arg1 * @param {Object} arg2 */NumberUtil.fn.mul=function(arg1,arg2)   {         var m=0,s1=arg1.toString(),s2=arg2.toString();         try{m+=s1.split(".")[1].length}catch(e){}         try{m+=s2.split(".")[1].length}catch(e){}         return Number(s1.replace(".",""))*Number(s2.replace(".",""))/Math.pow(10,m);     }     /** * 除 * @param {Object} arg1 * @param {Object} arg2 */NumberUtil.fn.div=function(arg1,arg2){           var t1=0,t2=0,r1,r2;           try{t1=arg1.toString().split(".")[1].length}catch(e){}           try{t2=arg2.toString().split(".")[1].length}catch(e){}      r1=Number(arg1.toString().replace(".",""));        r2=Number(arg2.toString().replace(".",""));           return (r1/r2)*Math.pow(10,t2-t1);}  /** * 四舍五入，保留指定位数 * @param {Object} num * @param {Object} n */NumberUtil.fn.round=function(num,n){    n=n||2;    if(isNaN(num)||num=="") return 0;    return Math.round(num*Math.pow(10,n))/Math.pow(10,n);};

下面浮点数计算为网络查找，并在非两位数都含有两位小数的情况下有效
一 js浮点数计算问题解决方案:

1.使用 NumberObject.toFixed(num) 方法

　toFixed() 方法可把 Number 四舍五入为指定小数位数的数字。

2.较精度计算浮点数

//说明：javascript的加法结果会有误差，在两个浮点数相加的时候会比较明显。这个函数返回较为精确的加法结果。 //调用：accAdd(arg1,arg2) //返回值：arg1加上arg2的精确结果     function accAdd(arg1, arg2) {     var r1, r2, m;     try {         r1 = (1 * arg1).toString().split(".")[1].length;     }     catch (e) {         r1 = 0;     }     try {         r2 = (1 * arg2).toString().split(".")[1].length;     }     catch (e) {         r2 = 0;     }     m = Math.pow(10, Math.max(r1, r2));     return (arg1 * m + arg2 * m) / m; }     //说明：javascript的减法结果会有误差，在两个浮点数相加的时候会比较明显。这个函数返回较为精确的减法结果。 //调用：accSub(arg1,arg2) //返回值：arg1减上arg2的精确结果     function accSub(arg1, arg2) {     return accAdd(arg1, -arg2); }     //说明：javascript的乘法结果会有误差，在两个浮点数相乘的时候会比较明显。这个函数返回较为精确的乘法结果。 //调用：accMul(arg1,arg2) //返回值：arg1乘以arg2的精确结果     function accMul(arg1, arg2) {     var m = 0, s1 = (1 * arg1).toString(), s2 = (1 * arg2).toString();     try {         m += s1.split(".")[1].length;     }     catch (e) {     }     try {         m += s2.split(".")[1].length;     }     catch (e) {     }     var ss = Number(s1.replace(".", "")) * Number(s2.replace(".", "")) / Math.pow(10, m);     return Math.round(ss * 100) / 100; }     //说明：javascript的除法结果会有误差，在两个浮点数相除的时候会比较明显。这个函数返回较为精确的除法结果。 //调用：accDiv(arg1,arg2) //返回值：arg1除以arg2的精确结果     function accDiv(arg1, arg2) {     var t1 = 0, t2 = 0, r1, r2;     try {         t1 = (1 * arg1).toString().split(".")[1].length;     }     catch (e) {     }     try {         t2 = (1 * arg2).toString().split(".")[1].length;     }     catch (e) {     }     with (Math) {         r1 = Number((1 * arg1).toString().replace(".", ""));         r2 = Number((1 * arg2).toString().replace(".", ""));         var ss = (r1 / r2) * pow(10, t2 - t1);         return Math.round(ss * 100) / 100;     } }　　

二 金额大写转换

//金额大小写转换 function convertCurrency(currencyDigits) { // Constants: var MAXIMUM_NUMBER = 99999999999.99; // Predefine the radix characters and currency symbols for output: var CN_ZERO = "零"; var CN_ONE = "壹"; var CN_TWO = "贰"; var CN_THREE = "叁"; var CN_FOUR = "肆"; var CN_FIVE = "伍"; var CN_SIX = "陆"; var CN_SEVEN = "柒"; var CN_EIGHT = "捌"; var CN_NINE = "玖"; var CN_TEN = "拾"; var CN_HUNDRED = "佰"; var CN_THOUSAND = "仟"; var CN_TEN_THOUSAND = "万"; var CN_HUNDRED_MILLION = "亿"; var CN_SYMBOL = "人民币"; var CN_DOLLAR = "元"; var CN_TEN_CENT = "角"; var CN_CENT = "分"; var CN_INTEGER = "整"; // Variables: var integral; // Represent integral part of digit number.  var decimal; // Represent decimal part of digit number. var outputCharacters; // The output result. var parts; var digits, radices, bigRadices, decimals; var zeroCount; var i, p, d; var quotient, modulus; // Validate input string: currencyDigits = currencyDigits.toString(); if (currencyDigits == "") {   alert("Empty input!");   return ""; } if (currencyDigits.match(/[^,.\d]/) != null) {   alert("Invalid characters in the input string!");   return ""; } if ((currencyDigits).match(/^((\d{1,3}(,\d{3})*(.((\d{3},)*\d{1,3}))?)|(\d+(.\d+)?))$/) == null) {   alert("Illegal format of digit number!");   return ""; } // Normalize the format of input digits: currencyDigits = currencyDigits.replace(/,/g, ""); // Remove comma delimiters. currencyDigits = currencyDigits.replace(/^0+/, ""); // Trim zeros at the beginning.  // Assert the number is not greater than the maximum number. if (Number(currencyDigits) > MAXIMUM_NUMBER) {   alert("Too large a number to convert!");   return ""; } // http://www.knowsky.com/ Process the coversion from currency digits to characters: // Separate integral and decimal parts before processing coversion: parts = currencyDigits.split("."); if (parts.length > 1) {   integral = parts[0];   decimal = parts[1];   // Cut down redundant decimal digits that are after the second.   decimal = decimal.substr(0, 2); } else {   integral = parts[0];   decimal = ""; } // Prepare the characters corresponding to the digits: digits = new Array(CN_ZERO, CN_ONE, CN_TWO, CN_THREE, CN_FOUR, CN_FIVE, CN_SIX, CN_SEVEN, CN_EIGHT,CN_NINE); radices = new Array("", CN_TEN, CN_HUNDRED, CN_THOUSAND); bigRadices = new Array("", CN_TEN_THOUSAND, CN_HUNDRED_MILLION); decimals = new Array(CN_TEN_CENT, CN_CENT); // Start processing: outputCharacters = ""; // Process integral part if it is larger than 0: if (Number(integral) > 0) {   zeroCount = 0;   for (i = 0; i < integral.length; i++) {    p = integral.length - i - 1;    d = integral.substr(i, 1);    quotient = p / 4;    modulus = p % 4;    if (d == "0") {     zeroCount++;    }    else {     if (zeroCount > 0)     {      outputCharacters += digits[0];     }     zeroCount = 0;     outputCharacters += digits[Number(d)] + radices[modulus];    }    if (modulus == 0 && zeroCount < 4) {      outputCharacters += bigRadices[quotient];    }   }   outputCharacters += CN_DOLLAR; } // Process decimal part if there is: if (decimal != "") {   for (i = 0; i < decimal.length; i++) {    d = decimal.substr(i, 1);    if (d != "0") {     outputCharacters += digits[Number(d)] + decimals[i];    }   } } // Confirm and return the final output string: if (outputCharacters == "") {   outputCharacters = CN_ZERO + CN_DOLLAR; } if (decimal == "") {   outputCharacters += CN_INTEGER; } //outputCharacters = CN_SYMBOL + outputCharacters; outputCharacters = outputCharacters; return outputCharacters; }//  //还原金额    function rmoney(s){      return parseFloat(s.replace(/[^\d\.-]/g,""));   }    //金额合计的格式化s为要格式化的参数（浮点型），n为小数点后保留的位数     function fmoney(s,n){     n = n>0 && n<=20 ? n : 2;     s = parseFloat((s+"").replace(/[^\d\.-]/g,"")).toFixed(n)+"";     var l = s.split(".")[0].split("").reverse(),      r = s.split(".")[1];      t = "";     for(i = 0;i<l.length;i++){         t+=l[i]+((i+1)%3==0 && (i+1) != l.length ? "," : "");      }     return t.split("").reverse().join("")+"."+r; }