Possible Javascript numerical bug

Question

This code snippet:

Math.pow(10,20)+20000 == Math.pow(10,20) + 10000

evaluates to true. Is this a JS bug?

no, this is IEEE floating point. – Mike 'Pomax' Kamermans Sep 19 '13 at 22:42 — Mike 'Pomax' Kamermans, Sep 19 '13 at 22:42
Check this http://floating-point-gui.de/ – elclanrs Sep 19 '13 at 22:43 — elclanrs, Sep 19 '13 at 22:43
The *slightest* search would tell you what's going on. – T.J. Crowder Sep 19 '13 at 22:47 — T.J. Crowder, Sep 19 '13 at 22:47

score 8 · Accepted Answer · answered Sep 19 '13 at 22:42

8

No. Javascript uses floating point numbers to represent large values, and the value 10²⁰ exceeds the precision of the floating point numbers. When you add a relatively tiny value such as 20000 or 10000 to the result, the resulting sums are indistinguishable.

answered Sep 19 '13 at 22:42

Greg Hewgill

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10^20 doesn't exceed the precision of FP numbers, what is at play here is the fact that floating point numbers are not evenly distributed (they become more and more sparse as their magnitude grows). – jmbr Sep 22 '13 at 14:12

Possible Javascript numerical bug

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