Inexact conversion

[devmotion]

Hi!

I just discovered the following strange behaviour when converting simple units:

julia> convert(typeof(1.0u"N"), 1e-3u"mN")
1.0e-6 N

julia> 1.0e-6u"N" == convert(typeof(1.0u"N"), 1e-3u"mN")
true

julia> convert(typeof(1.0u"N"), 1e-4u"mN")
1.0000000000000001e-7 N

julia> 1.0e-7u"N" == convert(typeof(1.0u"N"), 1e-4u"mN")
false

julia> convert(typeof(1.0u"N"), 1e-5u"mN")
1.0e-8 N

julia> 1.0e-8u"N" == convert(typeof(1.0u"N"), 1e-5u"mN")
true

I tested all other exponents with absolute value less or equal than 20, and the inexact conversion happens also for exponents -8, -9, -13, -17, and -18.

[ajkeller34]

If I have 1e-4u"mN" and I want to convert to N, I should divide by 1000, so:

julia> 1e-4/1000
1.0000000000000001e-7

On the other hand:

julia> 1e-3/1000
1.0e-6

What you observe seems to be a quirk of Float64, so I'm not sure I can address this.