The interop mechanism is called P/Invoke. In F# the P/Invoke declaration of a native function is usually pretty close to the C declaration, labelled as extern annotated with the System.Runtime.InteropServices.DllImportAttribute
Not knowing the library you are using here, I can't give closer specifics that that; though I expect that a decompression operation will involve byte arrays for data in and out -- there are helper types for array marshalling in the F# PowerPack, or you can
use the C# MarshalAs attribute on the buffer arguments.