Fix reshape layer output size computation

modules/dnn/src/layers/reshape_layer.cpp

@@ -55,6 +55,7 @@ static void computeShapeByReshapeMask(const MatShape &srcShape,
 {
     int srcShapeSize = (int)srcShape.size();
     int maskShapeSize = (int)maskShape.size();
+    int maskTotal = abs(total(maskShape));  // Mask might have negative ones.
 
     if (srcRange == Range::all())
         srcRange = Range(0, srcShapeSize);
@@ -65,6 +66,19 @@ static void computeShapeByReshapeMask(const MatShape &srcShape,
         srcRange.end = srcRange.end == INT_MAX ? srcShapeSize : srcRange.start + sz;
     }
 
+    if (maskTotal != 0)
+    {
+        for (int i = srcRange.start + 1; i < srcRange.end; ++i)
+        {
+            if (total(srcShape, i, srcRange.end) != maskTotal)
+            {
+                srcRange.start = i - 1;
+                break;
+            }
+        }
+        CV_Assert(total(srcShape, srcRange.start, srcRange.end) == maskTotal);
+    }
+
     CV_Assert(0 <= srcRange.start && srcRange.start <= srcRange.end && srcRange.end <= srcShapeSize);
     int dstShapeSize = srcShapeSize - srcRange.size() + maskShapeSize;
     dstShape.resize(dstShapeSize);

modules/dnn/test/test_torch_importer.cpp

@@ -122,6 +122,7 @@ TEST(Torch_Importer, run_reshape)
 {
     runTorchNet("net_reshape");
     runTorchNet("net_reshape_batch");
+    runTorchNet("net_reshape_single_sample");
 }
 
 TEST(Torch_Importer, run_linear)