How to obtain only the integer part of a long floating precision number with JS?

Question

I know there's

Math.floor
parseInt

But about this case:

Math.floor(1.99999999999999999999999999)

returning 2, how could I obtain only its integer part, equals to 1?

score 7 · Accepted Answer · edited May 23 '17 at 12:06

7

1.99999999999999999999999999 is not the actual value of the number. It has a value of 2 after the literal is parsed because this is 'as best' as JavaScript can represent such a value.

JavaScript numbers are IEEE-754 binary64 or "double precision" which allow for 15 to 17 significant [decimal] digits of precision - the literal shown requires 27 significant digits which results in information loss.

Test: 1.99999999999999999999999999 === 2 (which results in true).

Here is another answer of mine that describes the issue; the finite relative precision is the problem.

edited May 23 '17 at 12:06

Community

1
1

answered Aug 13 '15 at 23:42

user2864740

60,010
15
145
220

So I should rather use another language? COBOL? – diegoaguilar Aug 13 '15 at 23:42
@diegoaguilar To do.. what? You're using JavaScript for a reason :) – user2864740 Aug 13 '15 at 23:43
Numerical analysis app in a Node.js API – diegoaguilar Aug 13 '15 at 23:43
2

@diegoaguilar There are various libraries available to help with 'big numbers' or 'rationals' or 'fixed precision', etc. However JavaScript's number type is incapable of directly dealing with this situation. – user2864740 Aug 13 '15 at 23:46

How to obtain only the integer part of a long floating precision number with JS?

1 Answers1