expression calculation error

Prelude> 20^{65}-exp(65*log(20))

1. 211571712111507e70

Obviously, correct result is 0.

changed weight to 5

added Tbug Trac import labels

changed the description

closed

This is a precision issue with Double numbers:

> 2^21-exp(21*log(2)) :: Double
0.0
> 2^22-exp(22*log(2)) :: Double
-9.313225746154785e-10
> 2^22 :: Double
4194304.0
> exp(22*log(2)) :: Double
4194304.000000001

You get the same result with other languages:

php > echo (20**65 - exp(65*log(20))) ;
6.1252998827766E+70

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedInvalid

added Pnormal label