limit r by rshift

core/privc3/fixedpoint_tensor_imp.h

@@ -247,11 +247,7 @@ void FixedPointTensor<T, N>::truncate(const FixedPointTensor<T, N>* op,
         }
         // r'
         aby3_ctx()->template gen_random_private(*temp[0]);
-        std::for_each(temp[0]->data(), temp[0]->data() + temp[0]->numel(),
-                      [] (T& a) {
-                          a = (T) (a * std::pow(2, sizeof(T) * 8 - 2)
-                                   / std::numeric_limits<T>::max());
-                      });
+        temp[0]->rshift(1, temp[0].get());
 
         //r'_0, r'_1
         aby3_ctx()->template gen_random_private(*temp[1]);

core/privc3/fixedpoint_tensor_test.cc

@@ -3438,7 +3438,7 @@ TEST_F(FixedTensorTest, inv_sqrt_test) {
 }
 
 #ifdef USE_ABY3_TRUNC1 //use aby3 trunc1
-TEST_F(FixedTensorTest, truncate1_msb_failed) {
+TEST_F(FixedTensorTest, truncate1_msb_incorrect) {
     std::vector<size_t> shape = { 1 };
     std::shared_ptr<TensorAdapter<int64_t>> sl[3] = { gen(shape), gen(shape), gen(shape) };
     std::shared_ptr<TensorAdapter<int64_t>> sout[6] = { gen(shape), gen(shape), gen(shape),
@@ -3498,7 +3498,7 @@ TEST_F(FixedTensorTest, truncate1_msb_failed) {
 }
 
 #else
-TEST_F(FixedTensorTest, truncate3_msb_not_failed) {
+TEST_F(FixedTensorTest, truncate3_msb_correct) {
     std::vector<size_t> shape = { 1 };
     std::shared_ptr<TensorAdapter<int64_t>> sl[3] = { gen(shape), gen(shape), gen(shape) };
     std::shared_ptr<TensorAdapter<int64_t>> sout[6] = { gen(shape), gen(shape), gen(shape),