C++ :: Conversion Of Longitude And Latitude - Reverse Function

I have code for conversion of longitude and latitude and I need to reverse the function so it will work in opposite direction:

Code:
float LongitudeDeg = argv[1]; // some longitude
float LatitudeDeg = argv[2]; // some latitude
uint32_t u,v,l,n;
l=15; // l range is 2-29

[Code] .....

On start of the code we know longitude,latitude and l. And the result is u and v. And I need function when I will know the u and v, possibly l too, to calculate longitude, latitude.