With GCL we do not get overflow errors when converting bigfloat numbers into float numbers which are obviously too big to fit in a float number:
This is a correct example:
The following bigfloat numbers are too big. The result is unpredicable and wrong:
I have observed this for GCL 2.6.8. CLISP 2.44 gives an overflow error.
The problem is the Lisp function scale-float which is called by fp2flo in the file float.lisp.