js大数计算之计算

 1 <!DOCTYPE html>
 2 <html>
 3 
 4 <head>
 5     <meta charset="UTF-8">
 6     <title></title>
 7     <script>
 8     var old = 0.2878978 + 1.89;
 9     console.log(old);
10     console.log(strip(old));
11     var result = plus(0.2878978, 1.89);
12     console.log(result);
13 
14     console.log(3.1415926 * 79.85677809789);
15     var rc = times(3.1415926, 79.85677809789);
16     console.log(rc);
17 
18     /**
19      * 把错误的数据转正
20      * strip(0.09999999999999998)=0.1
21      */
22     function strip(num) {
23         var precision = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 12;
24 
25         return +parseFloat(num.toPrecision(precision));
26     }
27 
28     /**
29      * Return digits length of a number
30      * @param {*number} num Input number
31      */
32     function digitLength(num) {
33         // Get digit length of e
34         var eSplit = num.toString().split(/[eE]/);
35         var len = (eSplit[0].split('.')[1] || '').length - +(eSplit[1] || 0);
36         return len > 0 ? len : 0;
37     }
38 
39     /**
40      * 精确乘法
41      */
42     function times(num1, num2) {
43         var num1Changed = Number(num1.toString().replace('.', ''));
44         var num2Changed = Number(num2.toString().replace('.', ''));
45         var baseNum = digitLength(num1) + digitLength(num2);
46         return num1Changed * num2Changed / Math.pow(10, baseNum);
47     }
48 
49     /**
50      * 精确加法
51      */
52     function plus(num1, num2) {
53         var baseNum = Math.pow(10, Math.max(digitLength(num1), digitLength(num2)));
54         return (times(num1, baseNum) + times(num2, baseNum)) / baseNum;
55     }
56 
57     /**
58      * 精确减法
59      */
60     function minus(num1, num2) {
61         var baseNum = Math.pow(10, Math.max(digitLength(num1), digitLength(num2)));
62         return (times(num1, baseNum) - times(num2, baseNum)) / baseNum;
63     }
64 
65     /**
66      * 精确除法
67      */
68     function divide(num1, num2) {
69         var num1Changed = Number(num1.toString().replace('.', ''));
70         var num2Changed = Number(num2.toString().replace('.', ''));
71         return times(num1Changed / num2Changed, Math.pow(10, digitLength(num2) - digitLength(num1)));
72     }
73 
74     /**
75      * 四舍五入
76      */
77     function round(num, ratio) {
78         var base = Math.pow(10, ratio);
79         return divide(Math.round(times(num, base)), base);
80     }
81     </script>
82 </head>
83 
84 <body>
85 </body>
86 
87 </html>

业精于勤荒于嬉，行成于思毁于随

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原文地址：https://www.cnblogs.com/qixianchuan/p/11162506.html