money-arithmetics-prototype.js

//simple and correct math for money arithmetics

Number.prototype.add=function(a){ return parseFloat((this+a).toFixed(15)) };
Number.prototype.sub=function(a){ return parseFloat((this-a).toFixed(15)) };
Number.prototype.mul=function(a){ return parseFloat((this*a).toFixed(15)) };
Number.prototype.div=function(a){ return parseFloat((this/a).toFixed(15)) };


// use with one number each time.
//  > 0.1.add(0.1).add(0.1).mul(10).div(10)
//    0.3
//
//  > 0.1.add(0.2)
//    0.3 // correct result
//
//   0.1+0.2
//  0.30000000000000004
// incorrect result (correct up to 15 decimal points,
// due to iee 754 floating point encoding and decoding  of the stored number in memory, 
// theoretically, it is correct. but for real use it isn't. )