- cufinufft2d.cu
  This file contains the execution functions 2d type 1,2 that are called in ../cufinufft.cu

- spreadinterp2d.cu
  This file contains all the GPU kernels for 2d spreading, interpolation.

- interp2d_wrapper.cu
  Wrappers for 2d interpolations. Two methods are implemented: 
    (1) nonuniform driven, 
    (2) subproblem
    
- spread2d_wrapper.cu
  Wrappers for 2d spreading. Three methods are implemented: 
    (1) nonuniform driven, 
    (2) subproblem, 
