Python ffi

diffusion.c

/* filename: diffusion.c
 * compile:
 * gcc -O3 -std=gnu99 -c diffusion.c
 * gcc -shared -o diffusion.so diffusion.o
 *
 * .so file place /usr/lib or /usr/local/lib or set LD_LIBRARY_PATH for custom location
 */

void evolve(int w, int h, double **in, double **out, double D, double dt) {
  int i, j;
  double laplacian;
  for(i = 1; i < h; i++) {
    for(j = 1; j < w; j++) {
      laplacian = in[i+1][j] + in[i-1][j] + in[i][j+1] + in[i][j-1] - 4 * in[i][j];
      out[i][j] = in[i][j] + D * dt * laplacian;
    }
  }
}

diffusion_inline.py

ffi = FFI()
ffi.cdef(r'''void evolve(int Nx, int Ny, double **in, double **out, double D, double dt);''')
lib = ffi.verify(r'''
  void evolve(int Nx, int Ny, double in[][Ny], double out[][Ny], double D, double dt) {
    int i, j;
    double laplacian;
    for(i = 1; i < h; i++) {
      for(j = 1; j < w; j++) {
        laplacian = in[i+1][j] + in[i-1][j] + in[i][j+1] + in[i][j-1] - 4 * in[i][j];
        out[i][j] = in[i][j] + D * dt * laplacian;
      }
    }
  }
''', extra_compile_args=["-O3",]) # JIT compile
    

diffusion_main.py

# use cffi instead!
import ctypes

grid_shape = (512, 512)
_diffusion = ctypes.CDLL("diffusion.so")

TYPE_INT = ctypes.c_int
TYPE_DOUBLE = ctypes.c_double
TYPE_DOUBLE_SS = ctypes.POINTER(ctypes.POINTER(ctypes.c_double))

# void evolve(int, int, double**, double**, double, double)
_diffusion.evolve.argtypes = [TYPE_INT, TYPE_INT, TYPE_DOUBLE_SS, TYPE_DOUBLE_SS, TYPE_DOUBLE, TYPE_DOUBLE]
_diffusion.evolve.restype = None

def evolve(grid, out, dt, D=1.0):
  cX = TYPE_INT(grid_shape[0])
  cY = TYPE_INT(grid_shape[1])
  cdt = TYPE_DOUBLE(dt)
  cD = TYPE_DOUBLE(D)
  pointer_grid = grid.ctypes.data_ss(TYPE_DOUBLE_SS) # numpy array
  pointer_out = out.ctypes.data_as(TYPE_DOUBLE_SS) # numpy array
  
  _diffusion.evolve(cX, cY, pointer_grid, pointer_out, cD, cdt)

diffusion_main_cffi.py

from cffi import FFI

ffi = FFI()
ffi.cdef(r'''void evolve(int w, int h, double **in, double **out, double D, double dt);''')

lib = ffi.dlopen("diffusion.so")

grid_shape = (512, 512)

def evolve(grid, dt, out, D=1.0):
  X, Y = grid_shape
  pointer_grid = ffi.cast('double**', grid.ctypes.data)
  pointer_out = ffi.cast('double**' , out.ctypes.data)
  lib.evolve(X, Y, pointer_grid, pointer_out, D, dt)

struct.py

# Is this work as-is?
from cffi import FFI

ffi = FFI()
ffi.cdef(r'''
  struct Point {
    double x;
    double y;
    ...;
  };
  
  struct Point do_calculation();
''')

lib = ffi.verify(r'''
  #include "complecated.h"
''')