From 70d622ea54c55aa5489e71b769a92447a586c879 Mon Sep 17 00:00:00 2001
From: Joseph Redmon <pjreddie@gmail.com>
Date: Mon, 14 Jul 2014 05:07:51 +0000
Subject: [PATCH] Added batch to col2im, padding option

---
 src/im2col.c |   32 +++++++++++++++++++++++++-------
 1 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/src/im2col.c b/src/im2col.c
index 899f73a..42bddf5 100644
--- a/src/im2col.c
+++ b/src/im2col.c
@@ -1,27 +1,45 @@
 #include "mini_blas.h"
 
+inline float im2col_get_pixel(float *im, int height, int width, int channels,
+                        int row, int col, int channel, int pad)
+{
+    row -= pad;
+    col -= pad;
+
+    if (row < 0 || col < 0 ||
+        row >= height || col >= width) return 0;
+    return im[col + width*(row + channel*height)];
+}
+
 //From Berkeley Vision's Caffe!
 //https://github.com/BVLC/caffe/blob/master/LICENSE
 void im2col_cpu(float* data_im,
     const int batch, const int channels, const int height, const int width,
-    const int ksize, const int stride, float* data_col) 
+    const int ksize, const int stride, int pad, float* data_col) 
 {
     int c,h,w,b;
     int height_col = (height - ksize) / stride + 1;
     int width_col = (width - ksize) / stride + 1;
+    if (pad){
+        height_col = 1 + (height-1) / stride;
+        width_col = 1 + (width-1) / stride;
+        pad = ksize/2;
+    }
     int channels_col = channels * ksize * ksize;
     int im_size = height*width*channels;
     int col_size = height_col*width_col*channels_col;
-    for(b = 0; b < batch; ++b){
-        for ( c = 0; c < channels_col; ++c) {
+    for (b = 0; b < batch; ++b) {
+        for (c = 0; c < channels_col; ++c) {
             int w_offset = c % ksize;
             int h_offset = (c / ksize) % ksize;
             int c_im = c / ksize / ksize;
-            for ( h = 0; h < height_col; ++h) {
-                for ( w = 0; w < width_col; ++w) {
+            for (h = 0; h < height_col; ++h) {
+                for (w = 0; w < width_col; ++w) {
+                    int im_row = h_offset + h * stride;
+                    int im_col = w_offset + w * stride;
                     data_col[(c * height_col + h) * width_col + w] =
-                    data_im[(c_im * height + h * stride + h_offset) * width
-                        + w * stride + w_offset];
+                        im2col_get_pixel(data_im, height, width, channels,
+                                        im_row, im_col, c_im, pad);
                 }
             }
         }

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