- cufinufft3d.cu
  This file contains the execution functions for 3d type1,2 that are called in ../cufinufft.cu

- spreadinterp3d.cu
  This file contains all the GPU kernels for 3d spreading, interpolation.

- interp3d_wrapper.cu
  Wrappers for 3d interpolations. Two methods are implemented: 
    (1) nonuniform driven, 
    (2) subproblem
    
- spread3d_wrapper.cu
  Wrappers for 3d spreading. Three methods are implemented: 
    (1) nonuniform points driven, 
    (2) subproblem, 
    (4) block gather 
