integer64 foreign type ( manual/Foreign%20type%20specifiers.html )

The manual (git current version) says:

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integer64type
unsigned-integer64type
A fixnum or integral flonum, mapping to int64_t or uint64_t. When 
outside of fixnum range the value will overflow into a flonum.

[...] (Numbers between 2^62 and 2^64-1 have gaps.)

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First of all I don't understand why it's documented as integerNNtype 
when in foreign prims/values one uses "integerNN", not "integerNNtype", 
both as arguments and return values.


But also I don't see any "flonum" (float or double I assume) in 
translated C code. Instead I see things like "C_int64_to_num" which 
seems to return bignums when out of fixnum range; no flonums, no gaps, 
values print out as integers, (exact? ...) prints #t even for 
(u)int64-max. Is the documentation out of date?


Thanks, Al