Function to make a struct timespec from a floating point number?

[Po Lu]

I recall there being a function in the Emacs sources to construct a
`struct timespec' from a floating point number denoting seconds.

I would like to use it to allow setting `polling-period' to a period
less than one second, so that C-g can be detected faster in the NS port.

Does anyone remember the name of that function, if it does exist?  I
don't want to reinvent the wheel.

Thanks.