first c try

.gitignore

+__pycache__/
+_ext/
+build/
+dist/
+*.egg-info/
+*.so

build.py

+from os import path as osp
+
+from torch.utils.ffi import create_extension
+
+abs_path = osp.join(osp.dirname(osp.realpath(__file__)), 'torch_scatter')
+
+headers = ['torch_scatter/include/scatter.h']
+sources = ['torch_scatter/src/scatter.c']
+includes = [osp.join(abs_path, 'include'), osp.join(abs_path, 'src')]
+defines = []
+extra_objects = []
+with_cuda = False
+
+ffi = create_extension(
+    name='torch_scatter._ext.scatter',
+    package=True,
+    verbose=True,
+    headers=headers,
+    sources=sources,
+    includes=includes,
+    define_macros=defines,
+    extra_objects=extra_objects,
+    with_cuda=with_cuda,
+    relative_to=__file__)
+
+if __name__ == '__main__':
+    ffi.build()

setup.py

+from os import path as osp
+from setuptools import setup, find_packages
+
+import build  # noqa
+
+setup(
+    name='pytorch_scatter',
+    version='0.1',
+    description='PyTorch extension for various scatter methods',
+    url='https://github.com/rusty1s/pytorch_scatter',
+    author='Matthias Fey',
+    author_email='matthias.fey@tu-dortmund.de',
+    install_requires=['cffi>=1.0.0'],
+    setup_requires=['cffi>=1.0.0'],
+    packages=find_packages(exclude=['build']),
+    ext_package='',
+    cffi_modules=[osp.join(osp.dirname(__file__), 'build.py:ffi')], )

torch_scatter/include/scatter.h

+void scatter_add_Float (THFloatTensor  *output, THLongTensor *index, THFloatTensor  *input, int dim);
+void scatter_add_Double(THDoubleTensor *output, THLongTensor *index, THDoubleTensor *input, int dim);
+void scatter_add_Byte  (THByteTensor   *output, THLongTensor *index, THByteTensor   *input, int dim);
+void scatter_add_Char  (THCharTensor   *output, THLongTensor *index, THCharTensor   *input, int dim);
+void scatter_add_Short (THShortTensor  *output, THLongTensor *index, THShortTensor  *input, int dim);
+void scatter_add_Int   (THIntTensor    *output, THLongTensor *index, THIntTensor    *input, int dim);
+void scatter_add_Long  (THLongTensor   *output, THLongTensor *index, THLongTensor   *input, int dim);

torch_scatter/src/generic/scatter.c

+#ifndef TH_GENERIC_FILE
+#define TH_GENERIC_FILE "generic/scatter.c"
+#else
+
+inline void check_(asserts)(THTensor *output, THLongTensor *index, THTensor *input, int dim) {
+  // Assert same dimensionality.
+  THArgCheck(dim >= 0 && dim < THTensor_(nDimension)(output), 4, "Index dimension is out of bounds");
+  THArgCheck(THLongTensor_nDimension(index) == THTensor_(nDimension)(input), 2, "Index tensor must have same dimensions as input tensor");
+  THArgCheck(THTensor_(nDimension)(input) == THTensor_(nDimension)(output), 3, "Input tensor must have same dimensions as output tensor");
+
+  // Assert same tensor sizes across index and input.
+  THLongStorage *indexDims = THLongTensor_newSizeOf(index);
+  THArgCheck(THTensor_(isSize)(input, indexDims), 2, "Index tensor must have the same size as input tensor.");
+  THLongStorage_free(indexDims);
+
+  // Assert same tensor sizes across input and output apart from specified dimension.
+  for (int d = 0; d < THTensor_(nDimension)(output); d++) {
+    if (d != dim) THArgCheck(THTensor_(size)(output, d) == THTensor_(size)(input, d), 3, "Input tensor must have same size as output tensor apart from the specified dimension");
+  }
+}
+
+void scatter_(add)(THTensor *output, THLongTensor *index, THTensor *input, int dim) {
+  check_(asserts)(output, index, input, dim); long idx;
+  TH_TENSOR_DIM_APPLY3(real, output, real, input, long, index, dim,
+    for (int i = 0; i < THLongTensor_size(index, dim); i++) {
+      idx = *(index_data + i * index_stride);
+      check_inBoundaries(idx, output_size, TH_TENSOR_DIM_APPLY_counter);
+      output_data[idx] += *(input_data + i * input_stride);
+    })
+}
+
+#endif

torch_scatter/src/scatter.c

+#include <TH/TH.h>
+
+#define scatter_(NAME) TH_CONCAT_4(scatter_, NAME, _, Real)
+#define check_(NAME) TH_CONCAT_4(check_, NAME, _, Real)
+
+inline void check_inBoundaries(int idx, int size, long *free) {
+  if (idx < 0 || idx >= size) { THFree(free); THError("Invalid index"); }
+}
+
+#include "generic/scatter.c"
+#include "THGenerateAllTypes.h"