Implements Quantized LSTM op for R. Also adds support for TENSOR_QUANT8_ASYMM_SIGNED in Test Generator. Bug: 144841609 Bug: 145916330 Test: NeuralNetworksTest_static Change-Id: I14b0d284b1945833d532cbaa33c66e4d77afd8b7 Merged-In: I14b0d284b1945833d532cbaa33c66e4d77afd8b7 (cherry picked from commit bac873a7b95af0338bc7da32c0fffe49bbd56181)

diff --git a/common/OperationsUtils.cpp b/common/OperationsUtils.cpp
index 2cac8b3..418045e 100644
--- a/common/OperationsUtils.cpp
+++ b/common/OperationsUtils.cpp

@@ -211,6 +211,20 @@
         ++*shift;
     }
     NN_RET_CHECK_LE(q_fixed, std::numeric_limits<int32_t>::max());
+    // A shift amount smaller than -31 would cause all bits to be shifted out
+    // and thus all results would be zero. We implement that instead with
+    // q_fixed==0, so as to avoid hitting issues with right-shift
+    // operations with shift amounts greater than 31. Note that this happens
+    // roughly when abs(double_multiplier) < 2^-31 and the present handling means
+    // that we're effectively flushing tiny double_multiplier's to zero.
+    // We could conceivably handle values in the range (roughly) [32, 63]
+    // as 'denormals' i.e. (shift==0, q_fixed < 2^30). In that point of view
+    // the present handling is just doing 'flush denormals to zero'. We could
+    // reconsider and actually generate nonzero denormals if a need arises.
+    if (*shift < -31) {
+        *shift = 0;
+        q_fixed = 0;
+    }
     *quantized_multiplier = static_cast<int32_t>(q_fixed);
     return true;
 }