fixed up for PR

src/targets/cpu/cpu_lowering.cpp

@@ -141,7 +141,7 @@ struct cpu_im2col
     static std::string name() { return "cpu::im2col"; }
     shape compute_shape(const std::vector<shape>& inputs) const { return op.compute_shape(inputs); }
 
-    argument compute(context&, shape output_shape, std::vector<argument> args) const
+    argument compute(context&, const shape& output_shape, std::vector<argument> args) const
     {
         argument result{output_shape};
         auto input_shape   = args[0].get_shape();
@@ -157,18 +157,15 @@ struct cpu_im2col
             const std::size_t& stride_h = op.stride[0];
             const std::size_t& stride_w = op.stride[1];
 
-            int ksize = kernel_h * kernel_w * channels;
             int kdiv2_h, kdiv2_w;
             kdiv2_h = kernel_h / 2;
             kdiv2_w = kernel_w / 2;
             // calculate output sizes
             const std::size_t col_height = (height - kernel_h + 2 * pad_h) / stride_h + 1;
             const std::size_t col_width  = (width - kernel_w + 2 * pad_w) / stride_w + 1;
-            // calculate number of pixels in frame
-            const std::size_t npixels = height * width;
-            // starting pixel positions
+            // account for padding for the starting position of the input pixels
             std::size_t iinput = kdiv2_h - pad_h;
-            // loop over output pixels
+            // loop over output pixels (ioutput, joutput)
             for(std::size_t ioutput = 0; ioutput < col_height; ioutput++, iinput += stride_h)
             {
                 std::size_t jinput = kdiv2_w - pad_w;
@@ -181,14 +178,8 @@ struct cpu_im2col
                         [&](std::size_t c, std::size_t koffset, std::size_t loffset) {
                             int idx = iinput + koffset - kdiv2_h;
                             int jdx = jinput + loffset - kdiv2_w;
-                            if((idx >= 0) && (idx < height) && (jdx >= 0) && (jdx < width))
-                            {
-                                col[ldx * ksize + p] = input[c * npixels + idx * width + jdx];
-                            }
-                            else
-                            {
-                                col[ldx * ksize + p] = 0;
-                            }
+                            col(ldx, p) = ((idx >= 0) && (idx < height) && (jdx >= 0) && (jdx < width)) ?
+                              input(0, c, idx, jdx) : 0;
                             p++;
                         });
                 }