precision of gamma function

Dear R users,

I have to calculate gamma functions for negative numbers beyond -171.4.
e.x. gamma(-500.4)
I got following:

gamma(-170.4)

[1] -5.824625e-308

gamma(-171.4)

[1] 0
Warning message:
underflow occurred in 'gammafn'

I have tried to use a recursion getting values a little futher -180.
How could I solve this problem? Thank you beforehand.

Chuse.