Snippets from other packages/ License

Hello,

I want to use a function from another package (which is GPL>=3), about 20 lines of code, in my own package.
I somewhat hesitate to depend on the entire package just for this single function, but of course I want to credit the original authors.

What would be the best way to do that? Where should I put that credit? Or should I proceed completely different?

Why so shy about the name and location of this function?

 I think I've seen cases like this before, where a package has a handy
little function that has use outside the context of the package. In
that case I think the best thing is often for that function to be
taken out of that package completely, and put in a new package,
because it isn't so tightly coupled to the aims of the package.

 Obviously this is overkill for one function, but its possible there's
a few functions, or that they are handy enough to belong somewhere
else, such as the plotrix package if its a little plotting function,
or in one of Hadley's packages if it has an underscore in the name.

Barry