refine layer gradient test of ROIPoolLayer

paddle/gserver/tests/test_LayerGrad.cpp

@@ -1842,17 +1842,20 @@ TEST(Layer, roi_pool) {
   roiPoolConf->set_width(14);
   roiPoolConf->set_height(14);
 
-  MatrixPtr roiValue = Matrix::create(10, 10, false, false);
+  const size_t roiNum = 10;
+  const size_t roiDim = 10;
+  const size_t batchSize = 5;
+  MatrixPtr roiValue = Matrix::create(roiNum, roiDim, false, false);
   roiValue->zeroMem();
   real* roiData = roiValue->getData();
-  for (size_t i = 0; i < roiValue->getElementCnt() / 5; ++i) {
-    *roiData++ = std::rand() % 2;
-    *roiData++ = std::rand() % 224;
-    *roiData++ = std::rand() % 224;
-    size_t xMin = static_cast<size_t>(*(roiData - 2));
-    size_t yMin = static_cast<size_t>(*(roiData - 1));
-    *roiData++ = xMin + std::rand() % (224 - xMin);
-    *roiData++ = yMin + std::rand() % (224 - yMin);
+  for (size_t i = 0; i < roiNum; ++i) {
+    roiData[i * roiDim + 0] = std::rand() % batchSize;
+    roiData[i * roiDim + 1] = std::rand() % 224;  // xMin
+    roiData[i * roiDim + 2] = std::rand() % 224;  // yMin
+    size_t xMin = static_cast<size_t>(roiData[i * roiDim + 1]);
+    size_t yMin = static_cast<size_t>(roiData[i * roiDim + 2]);
+    roiData[i * roiDim + 3] = xMin + std::rand() % (224 - xMin);  // xMax
+    roiData[i * roiDim + 4] = yMin + std::rand() % (224 - yMin);  // yMax
   }
 
   config.inputDefs.push_back({INPUT_DATA, "input", 3 * 14 * 14, {}});
@@ -1860,7 +1863,7 @@ TEST(Layer, roi_pool) {
   config.layerConfig.add_inputs();
 
   for (auto useGpu : {false, true}) {
-    testLayerGrad(config, "roi_pool", 5, false, useGpu, false);
+    testLayerGrad(config, "roi_pool", batchSize, false, useGpu, false);
   }
 }