From 293b292e0ff3e6055dceb807c4cb57fc7bacb226 Mon Sep 17 00:00:00 2001
From: chengduoZH <zhaochengduo@163.com>
Date: Tue, 19 Dec 2017 17:00:55 +0800
Subject: [PATCH] refine im2col

---
 paddle/operators/math/im2col.cc | 39 +++++++++++++++++++++++----------
 1 file changed, 27 insertions(+), 12 deletions(-)

diff --git a/paddle/operators/math/im2col.cc b/paddle/operators/math/im2col.cc
index 707ebf059..a746c267b 100644
--- a/paddle/operators/math/im2col.cc
+++ b/paddle/operators/math/im2col.cc
@@ -61,14 +61,22 @@ class Im2ColFunctor<paddle::operators::math::ColFormat::kCFO,
 
     const T* im_data = im.data<T>();
     T* col_data = col->data<T>();
-
+    int w_offset = -1;
+    int h_offset = 0;
+    int c_im = 0;
     for (int c = 0; c < channels_col; ++c) {
-      int w_offset = c % filter_width;
-      int h_offset = (c / filter_width) % filter_height;
-      int c_im = c / filter_width / filter_height;
+      ++w_offset;
+      if (UNLIKELY(w_offset == filter_width)) {
+        w_offset = 0;
+        ++h_offset;
+        if (UNLIKELY(h_offset == filter_height)) {
+          h_offset = 0;
+          ++c_im;
+        }
+      }
       for (int h = 0; h < col_height; ++h) {
+        int im_row_idx = h * stride[0] - padding[0] + h_offset * dilation[0];
         for (int w = 0; w < col_width; ++w) {
-          int im_row_idx = h * stride[0] - padding[0] + h_offset * dilation[0];
           int im_col_idx = w * stride[1] - padding[1] + w_offset * dilation[1];
           int col_idx = (c * col_height + h) * col_width + w;
           int im_idx = (im_row_idx + c_im * im_height) * im_width + im_col_idx;
@@ -127,19 +135,26 @@ class Col2ImFunctor<paddle::operators::math::ColFormat::kCFO,
     T* im_data = im->data<T>();
     const T* col_data = col.data<T>();
 
+    int w_offset = -1;
+    int h_offset = 0;
+    int c_im = 0;
     for (int c = 0; c < channels_col; ++c) {
-      int w_offset = c % filter_width;
-      int h_offset = (c / filter_width) % filter_height;
-      int c_im = c / filter_width / filter_height;
+      ++w_offset;
+      if (UNLIKELY(w_offset == filter_width)) {
+        w_offset = 0;
+        ++h_offset;
+        if (UNLIKELY(h_offset == filter_height)) {
+          h_offset = 0;
+          ++c_im;
+        }
+      }
       for (int h = 0; h < col_height; ++h) {
+        int im_row_idx = h * stride[0] - padding[0] + h_offset * dilation[0];
         for (int w = 0; w < col_width; ++w) {
-          int im_row_idx = h * stride[0] - padding[0] + h_offset * dilation[0];
           int im_col_idx = w * stride[1] - padding[1] + w_offset * dilation[1];
-
           if ((im_row_idx) >= 0 && (im_row_idx) < im_height &&
               (im_col_idx) >= 0 && (im_col_idx) < im_width) {
-            im_row_idx += c_im * im_height;
-            im_data[im_row_idx * im_width + im_col_idx] +=
+            im_data[(im_row_idx + c_im * im_height) * im_width + im_col_idx] +=
                 col_data[(c * col_height + h) * col_width + w];
           }
         }
-- 
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