New var creation with right bit shift shows incorrect result using same initializer

Offtopic: Try 0.1+0.2 in nodejs(v10.15.1) and in Espruino (2v04.6).
Results are 0.30000000000000004 for nodejs and 0.3 for Espruino.

That's Javascript, and you should always keep in mind how numbers are represented internally.

Ontopic (Espruino 2v04.6)

>Math.pow(2,19)
=524288

>915E6*Math.pow(2,19)
=479723519999999.9375

>915E6*524288
=479723520000000

and one fix is to manually round the pow result:

>915E6*Math.round(Math.pow(2,19))
=479723520000000

//because
>524288 === Math.pow(2,19)
=false

>524288 === Math.round(Math.pow(2,19))
=true

Another fix is to use 524288 instead of Math.pow(2,19) for this calculation.
And of course that result should be rounded before it is used for binary operations.