Pool2d supports adaptive param (#3448)

*Pool2d supports adaptive param

lite/backends/arm/math/pooling.cc

@@ -21,6 +21,17 @@ namespace paddle {
 namespace lite {
 namespace arm {
 namespace math {
+
+int AdaptStartIndex(int ph, int input_size, int output_size) {
+  return static_cast<int>(
+      floor(static_cast<double>(ph * input_size) / output_size));
+}
+
+int AdaptEndIndex(int ph, int input_size, int output_size) {
+  return static_cast<int>(
+      ceil(static_cast<double>((ph + 1) * input_size) / output_size));
+}
+
 void pooling_basic(const float* din,
                    float* dout,
                    int num,
@@ -88,15 +99,27 @@ void pooling_basic(const float* din,
 #pragma omp parallel for
       for (int ind_c = 0; ind_c < chin; ++ind_c) {
         for (int ind_h = 0; ind_h < hout; ++ind_h) {
-          int sh = ind_h * stride_h;
-          int eh = sh + kernel_h;
-          sh = (sh - pad_h) < 0 ? 0 : sh - pad_h;
-          eh = (eh - pad_h) > hin ? hin : eh - pad_h;
+          int sh, eh;
+          if (adaptive) {
+            sh = AdaptStartIndex(ind_h, hin, hout);
+            eh = AdaptEndIndex(ind_h, hin, hout);
+          } else {
+            sh = ind_h * stride_h;
+            eh = sh + kernel_h;
+            sh = (sh - pad_h) < 0 ? 0 : sh - pad_h;
+            eh = (eh - pad_h) > hin ? hin : eh - pad_h;
+          }
           for (int ind_w = 0; ind_w < wout; ++ind_w) {
-            int sw = ind_w * stride_w;
-            int ew = sw + kernel_w;
-            sw = (sw - pad_w) < 0 ? 0 : sw - pad_w;
-            ew = (ew - pad_w) > win ? win : ew - pad_w;
+            int sw, ew;
+            if (adaptive) {
+              sw = AdaptStartIndex(ind_w, win, wout);
+              ew = AdaptEndIndex(ind_w, win, wout);
+            } else {
+              sw = ind_w * stride_w;
+              ew = sw + kernel_w;
+              sw = (sw - pad_w) < 0 ? 0 : sw - pad_w;
+              ew = (ew - pad_w) > win ? win : ew - pad_w;
+            }
             float result = static_cast<float>(0);
             int dst_ind = (ind_n * chout + ind_c) * size_channel_out +
                           ind_h * wout + ind_w;