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#ifndef TH_GENERIC_FILE
#define TH_GENERIC_FILE "generic/SpatialMaxPooling.c"
#else
static int nn_(SpatialMaxPooling_updateOutput)(lua_State *L)
{
THTensor *input = luaT_checkudata(L, 2, torch_Tensor);
int kW = luaT_getfieldcheckint(L, 1, "kW");
int kH = luaT_getfieldcheckint(L, 1, "kH");
int dW = luaT_getfieldcheckint(L, 1, "dW");
int dH = luaT_getfieldcheckint(L, 1, "dH");
THTensor *indices = luaT_getfieldcheckudata(L, 1, "indices", torch_Tensor);
THTensor *output = luaT_getfieldcheckudata(L, 1, "output", torch_Tensor);
luaL_argcheck(L, input->nDimension == 3, 2, "3D tensor expected");
luaL_argcheck(L, input->size[2] >= kW && input->size[1] >= kH, 2, "input image smaller than kernel size");
// sizes
long nslices = input->size[0];
long iheight = input->size[1];
long iwidth = input->size[2];
long oheight = (iheight - kH) / dH + 1;
long owidth = (iwidth - kW) / dW + 1;
// get contiguous input
input = THTensor_(newContiguous)(input);
// resize output
THTensor_(resize3d)(output, nslices, oheight, owidth);
// indices will contain i,j locatyions for each output point
THTensor_(resize4d)(indices, 2, nslices, oheight, owidth);
// get raw pointers
real *input_data = THTensor_(data)(input);
real *output_data = THTensor_(data)(output);
real *indices_data = THTensor_(data)(indices);
// compute max pooling for each input slice
long k;
#pragma omp parallel for private(k)
for (k = 0; k < nslices; k++) {
// pointers to slices
real *input_p = input_data + k*iwidth*iheight;
real *output_p = output_data + k*owidth*oheight;
real *indy_p = indices_data + k*owidth*oheight;
real *indx_p = indices_data + (k+nslices)*owidth*oheight;
// loop over output
int i,j;
for(i = 0; i < oheight; i++) {
for(j = 0; j < owidth; j++) {
// local pointers
real *ip = input_p + i*iwidth*dH + j*dW;
real *op = output_p + i*owidth + j;
real *indyp = indy_p + i*owidth + j;
real *indxp = indx_p + i*owidth + j;
// compute local max:
long maxindex = -1;
real maxval = -THInf;
long tcntr = 0;
int x,y;
for(y = 0; y < kH; y++) {
for(x = 0; x < kW; x++) {
real val = *(ip + y*iwidth + x);
if (val > maxval) {
maxval = val;
maxindex = tcntr;
}
tcntr++;
}
}
// set output to local max
*op = maxval;
// store location of max (x,y)
*indyp = (int)(maxindex / kW)+1;
*indxp = (maxindex % kW) +1;
}
}
}
// cleanup
THTensor_(free)(input);
return 1;
}
static int nn_(SpatialMaxPooling_updateGradInput)(lua_State *L)
{
THTensor *input = luaT_checkudata(L, 2, torch_Tensor);
THTensor *gradOutput = luaT_checkudata(L, 3, torch_Tensor);
int dW = luaT_getfieldcheckint(L, 1, "dW");
int dH = luaT_getfieldcheckint(L, 1, "dH");
THTensor *indices = luaT_getfieldcheckudata(L, 1, "indices", torch_Tensor);
THTensor *gradInput = luaT_getfieldcheckudata(L, 1, "gradInput", torch_Tensor);
// get contiguous gradOutput
gradOutput = THTensor_(newContiguous)(gradOutput);
// resize
THTensor_(resizeAs)(gradInput, input);
THTensor_(zero)(gradInput);
// sizes
int ichannels = input->size[0];
int iheight = input->size[1];
int iwidth = input->size[2];
int ochannels = ichannels;
int oheight = gradOutput->size[1];
int owidth = gradOutput->size[2];
// get raw pointers
real *gradInput_data = THTensor_(data)(gradInput);
real *gradOutput_data = THTensor_(data)(gradOutput);
real *indices_data = THTensor_(data)(indices);
// backprop
long k;
for (k = 0; k < input->size[0]; k++) {
// pointers to slices
real *gradOutput_p = gradOutput_data + k*owidth*oheight;
real *gradInput_p = gradInput_data + k*iwidth*iheight;
real *indy_p = indices_data + k*owidth*oheight;
real *indx_p = indices_data + (k+ochannels)*owidth*oheight;
// calculate max points
int i,j;
for(i = 0; i < oheight; i++) {
for(j = 0; j < owidth; j++) {
// retrieve position of max
long maxi = *(indy_p + i*owidth + j) - 1 + i*dH;
long maxj = *(indx_p + i*owidth + j) - 1 + j*dW;
// update gradient
*(gradInput_p + maxi*iwidth + maxj) += *(gradOutput_p + i*owidth + j);
}
}
}
// cleanup
THTensor_(free)(gradOutput);
return 1;
}
static const struct luaL_Reg nn_(SpatialMaxPooling__) [] = {
{"SpatialMaxPooling_updateOutput", nn_(SpatialMaxPooling_updateOutput)},
{"SpatialMaxPooling_updateGradInput", nn_(SpatialMaxPooling_updateGradInput)},
{NULL, NULL}
};
static void nn_(SpatialMaxPooling_init)(lua_State *L)
{
luaT_pushmetatable(L, torch_Tensor);
luaT_registeratname(L, nn_(SpatialMaxPooling__), "nn");
lua_pop(L,1);
}
#endif
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