big number printout

Not sure this is a bug, but it is confusing:

gosh> (gauche-version)
"0.8.13"
gosh> (+ 40816513889983671.0 3.0)
4.081651388998367e16
gosh> (= (+ 40816513889983671.0 3.0) 4.081651388998367e16)   
#t
gosh> (= (+ 40816513889983671.0 3.0) 40816513889983674.0)
#t
gosh> (= 40816513889983670.0 40816513889983674.0)
#t
gosh> (= 4.0816513889983670 4.0816513889983674) 
#f

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