diff --git a/SeqGRU.lua b/SeqGRU.lua
index 6b772f6..9cc4ac9 100644
--- a/SeqGRU.lua
+++ b/SeqGRU.lua
@@ -97,7 +97,12 @@ function SeqGRU:updateOutput(input)
 
    local h = self.output
    h:resize(seqlen, batchsize, outputsize):zero()
-   self.gates:resize(seqlen, batchsize, 3 * outputsize):zero()
+
+   local nElement = self.gates:nElement()
+   self.gates:resize(seqlen, batchsize, 3 * outputsize)
+   if nElement ~= seqlen * batchsize * 3 * outputsize then
+      self.gates:zero()
+   end
 
    local prev_h = h0
    if input.nn and input.nn.StepGRU_updateOutput and not self.forceLua then
@@ -184,7 +189,8 @@ function SeqGRU:backward(input, gradOutput, scale)
          local u = self.gates[{t, {}, {outputsize + 1, 2 * outputsize}}]
          local hc = self.gates[{t, {}, {2 * outputsize + 1, 3 * outputsize}}]
 
-         local grad_a = self.grad_a_buffer:resize(batchsize, 3 * outputsize):zero()
+         local grad_a = self.grad_a_buffer:resize(batchsize, 3 * outputsize)
+
          local grad_ar = grad_a[{{}, {1, outputsize}}]
          local grad_au = grad_a[{{}, {outputsize + 1, 2 * outputsize}}]
          local grad_ahc = grad_a[{{}, {2 * outputsize + 1, 3 * outputsize}}]
@@ -192,7 +198,7 @@ function SeqGRU:backward(input, gradOutput, scale)
          -- use grad_au as temporary buffer to compute grad_ahc.
 
          local grad_hc = grad_au:fill(0):addcmul(grad_next_h, -1, u, grad_next_h)
-         grad_ahc:fill(1):addcmul(-1, hc,hc):cmul(grad_hc)
+         grad_ahc:fill(1):addcmul(-1, hc, hc):cmul(grad_hc)
          local grad_r = grad_au:fill(0):addmm(grad_ahc, Wh[{{}, {2 * outputsize + 1, 3 * outputsize}}]:t() ):cmul(prev_h)
          grad_ar:fill(1):add(-1, r):cmul(r):cmul(grad_r)
 
diff --git a/SeqLSTM.lua b/SeqLSTM.lua
index 36cefca..2f54e54 100644
--- a/SeqLSTM.lua
+++ b/SeqLSTM.lua
@@ -145,7 +145,12 @@ function SeqLSTM:updateOutput(input)
    local h, c = self.output, self.cell
    h:resize(seqlen, batchsize, outputsize)
    c:resize(seqlen, batchsize, hiddensize)
+
+   local nElement = self.gates:nElement()
    self.gates:resize(seqlen, batchsize, 4 * hiddensize)
+   if nElement ~= seqlen * batchsize * 4 * hiddensize then
+      self.gates:zero()
+   end
 
    local prev_h, prev_c = h0, c0
    if input.nn and input.nn.StepLSTM_updateOutput and not self.forceLua then
diff --git a/StepGRU.lua b/StepGRU.lua
index ea50c71..b149db4 100644
--- a/StepGRU.lua
+++ b/StepGRU.lua
@@ -52,8 +52,12 @@ function StepGRU:updateOutput(input)
       local Wh = self.weight:narrow(1, inputsize + 1, self.outputsize)
 
       next_h:resize(batchsize, outputsize)
-      self.gates:resize(batchsize, 3 * outputsize):zero()
       local gates = self.gates
+      local nElement = gates:nElement()
+      gates:resize(batchsize, 3 * outputsize)
+      if gates:nElement() ~= batchsize * 3 * outputsize then
+         gates:zero()
+      end
 
       gates:addmm(bias_expand, cur_x, Wx)
       local sub_gates = gates:narrow(2, 1, 2 * outputsize)
@@ -92,7 +96,6 @@ function StepGRU:backward(input, gradOutput, scale)
    scale = scale or 1.0
    assert(scale == 1.0, 'must have scale=1')
 
-   --
    local grad_gates = torch.getBuffer('StepGRU', 'grad_gates', self.gates) -- batchsize x 3*outputsize
    local buffer = torch.getBuffer('StepGRU', 'buffer', self.gates) -- 1 x 3*outputsize
 
@@ -125,7 +128,8 @@ function StepGRU:backward(input, gradOutput, scale)
       local update_gate = gates:narrow(2, outputsize + 1, outputsize)
       local hidden_candidate = gates:narrow(2, 2 * outputsize + 1, outputsize)
 
-      grad_gates:resize(batchsize, 3 * outputsize):zero()
+      grad_gates:resize(batchsize, 3 * outputsize)
+
       local grad_reset_gate = grad_gates:narrow(2, 1, outputsize)
       local grad_update_gate = grad_gates:narrow(2, outputsize + 1, outputsize)
       local grad_hidden_candidate = grad_gates:narrow(2, 2 * outputsize + 1, outputsize)
diff --git a/StepLSTM.lua b/StepLSTM.lua
index 7285105..f3d4b1b 100644
--- a/StepLSTM.lua
+++ b/StepLSTM.lua
@@ -82,8 +82,12 @@ function StepLSTM:updateOutput(input)
       next_h:resize(batchsize, hiddensize)
       next_c:resize(batchsize, hiddensize)
 
-      self.gates:resize(batchsize, 4 * hiddensize):zero()
       local gates = self.gates
+      local nElement = gates:nElement()
+      gates:resize(batchsize, 4 * hiddensize)
+      if gates:nElement() ~= batchsize * 4 * hiddensize then
+         gates:zero()
+      end
 
       -- forward
       gates:addmm(bias_expand, cur_x, Wx)
@@ -182,7 +186,8 @@ function StepLSTM:backward(input, gradOutput, scale)
       local output_gate = gates[{{}, {2 * hiddensize + 1, 3 * hiddensize}}]
       local input_transform = gates[{{}, {3 * hiddensize + 1, 4 * hiddensize}}]
 
-      grad_gates:resize(batchsize, 4 * hiddensize):zero()
+      grad_gates:resize(batchsize, 4 * hiddensize)
+
       local grad_input_gate = grad_gates[{{}, {1, hiddensize}}]
       local grad_forget_gate = grad_gates[{{}, {hiddensize + 1, 2 * hiddensize}}]
       local grad_output_gate = grad_gates[{{}, {2 * hiddensize + 1, 3 * hiddensize}}]
diff --git a/benchmark/README.md b/benchmark/README.md
index 1f7a046..eac7edd 100644
--- a/benchmark/README.md
+++ b/benchmark/README.md
@@ -1,4 +1,4 @@
 # Benchmark
 
-On CPU, using Ubuntu 16.04, using float32, Torch LSTM boasts 886 samples/sec compared to TF’s 809 samples/sec for LSTM with 512 hiddensize and 64 batchsize.
-On the other hand, for 128 hiddensize and 32 batchsize, Torch has 3950 compared to TF’s 4130 samples/sec.
\ No newline at end of file
+On CPU, using Ubuntu 16.04, using float32, Torch LSTM boasts 900 samples/sec compared to TF’s 809 samples/sec for LSTM with 512 hiddensize and 64 batchsize.
+On the other hand, for 128 hiddensize and 32 batchsize, Torch has 3990 compared to TF’s 4130 samples/sec.
\ No newline at end of file
diff --git a/generic/StepGRU.c b/generic/StepGRU.c
index e17a5ad..93da17a 100644
--- a/generic/StepGRU.c
+++ b/generic/StepGRU.c
@@ -22,7 +22,10 @@ static int nn_(StepGRU_updateOutput)(lua_State *L) {
   buffer->size[0] = batchsize;
 
   THTensor_(resize2d)(next_h, batchsize, outputsize);
+  long nElement = THTensor_(nElement)(gates);
   THTensor_(resize2d)(gates, batchsize, 3 * outputsize);
+  if (nElement != batchsize * 3 * outputsize)
+    THTensor_(fill)(gates, 0);
 
   THTensor *Wx = THTensor_(newNarrow)(weight, 0, 0, inputsize);
   THTensor *Wh = THTensor_(newNarrow)(weight, 0, inputsize, outputsize);
@@ -32,8 +35,6 @@ static int nn_(StepGRU_updateOutput)(lua_State *L) {
   THTensor *update_gate = THTensor_(newNarrow)(gates, 1, outputsize, outputsize); // u = sig(Wx * x + Wh * prev_h + b)
   THTensor *hidden_candidate = THTensor_(newNarrow)(gates, 1, 2*outputsize, outputsize); // hc = tanh(Wx * x + Wh * r . prev_h + b)
 
-  //THTensor_(fill)(gates, 0);
-
   // forward
   THTensor_(addmm)(gates, 1, buffer, 1, cur_x, Wx);
   THTensor_(addmm)(sub_gates, 1, sub_gates, 1, prev_h, sub_Wh);
@@ -84,7 +85,6 @@ static int nn_(StepGRU_backward)(lua_State *L) {
   THTensor_(resize2d)(grad_cur_x, batchsize, inputsize);
   THTensor_(resize2d)(grad_prev_h, batchsize, outputsize);
   THTensor_(resize2d)(grad_gates, batchsize, 3 * outputsize);
-  THTensor_(fill)(grad_gates, 0);
 
   THTensor *Wx = THTensor_(newNarrow)(weight, 0, 0, inputsize);
   THTensor *Wh = THTensor_(newNarrow)(weight, 0, inputsize, outputsize);
diff --git a/generic/StepLSTM.c b/generic/StepLSTM.c
index 3e46d6f..d64449e 100644
--- a/generic/StepLSTM.c
+++ b/generic/StepLSTM.c
@@ -29,9 +29,10 @@ static int nn_(StepLSTM_updateOutput)(lua_State *L) {
 
   THTensor_(resize2d)(next_h, batchsize, hiddensize);
   THTensor_(resize2d)(next_c, batchsize, hiddensize);
-
+  long nElement = THTensor_(nElement)(gates);
   THTensor_(resize2d)(gates, batchsize, 4 * hiddensize);
-  //THTensor_(fill)(gates, 0);
+  if (nElement != batchsize * 4 * hiddensize)
+    THTensor_(fill)(gates, 0);
 
   // forward
   THTensor_(addmm)(gates, 1, buffer, 1, cur_x, Wx);
@@ -147,7 +148,6 @@ static int nn_(StepLSTM_backward)(lua_State *L) {
   THTensor *grad_Wh = THTensor_(newNarrow)(gradWeight, 0, inputsize, outputsize);
 
   THTensor_(resize2d)(grad_gates, batchsize, 4 * hiddensize);
-  THTensor_(fill)(grad_gates, 0);
 
   THTensor *grad_input_gate = THTensor_(newNarrow)(grad_gates, 1, 0, hiddensize);
   THTensor *grad_forget_gate = THTensor_(newNarrow)(grad_gates, 1, hiddensize, hiddensize);
diff --git a/test/README.md b/test/README.md
index b104498..49d8142 100644
--- a/test/README.md
+++ b/test/README.md
@@ -36,4 +36,48 @@ fast LSTM memory: 98.27904510498:2.2750110626221 MB
 step LSTM memory: 17.168065071106:2.1289348602295 MB
 rec LSTM memory: 13.374607086182:2.0407600402832 MB
 seq LSTM memory: 8.8895826339722:3.0098876953125 MB
+```
+
+More optimizations
+
+```
+th -lrnn -e 'rnn.bigtest({"LSTM","GRU"})'
+Running 3 tests
+1/3 LSTM_char_rnn ....................................................... [PASS]
+2/3 GRU ................................................................. [WAIT]CPU test
+old GRU time: 0.039725697040558 seconds
+step GRU time: 0.014464259147644 seconds
+luarec GRU time: 0.017707204818726 seconds
+rec GRU time: 0.013900947570801 seconds
+luaseq GRU time: 0.016570293903351 seconds
+seq GRU time: 0.012663447856903 seconds
+RecGRU-C 1.2738127907136 faster than RecGRU-Lua
+RecGRU 2.8577690001509 faster than old GRU
+SeqGRU 1.0977221786579 faster than RecGRU
+SeqGRU-C 1.3085136126113 faster than SeqGRU-Lua
+Memory test
+old GRU memory: 82.804834365845:1.833381652832 MB
+step GRU memory: 10.018351554871:1.5651426315308 MB
+rec GRU memory: 10.018255233765:1.5337238311768 MB
+seq GRU memory: 6.3827362060547:1.5385322570801 MB
+2/3 GRU ................................................................. [PASS]
+3/3 LSTM ................................................................ [WAIT]CPU test
+fast LSTM time: 0.044381546974182 seconds
+step LSTM time: 0.021313452720642 seconds
+luarec LSTM time: 0.021889448165894 seconds
+rec LSTM time: 0.017923295497894 seconds
+luaseq LSTM time: 0.018705642223358 seconds
+seq LSTM time: 0.016467046737671 seconds
+RecLSTM-C 1.2212847893104 faster than RecLSTM-Lua
+RecLSTM 2.476193453341 faster than FastLSTM
+SeqLSTM 1.0884341183591 faster than RecLSTM
+SeqLSTM-C 1.1359439565181 faster than SeqLSTM-Lua
+Memory test
+fast LSTM memory: 98.2790184021:2.2749843597412 MB
+step LSTM memory: 17.168484687805:2.1293544769287 MB
+rec LSTM memory: 13.375099182129:2.0412521362305 MB
+seq LSTM memory: 8.8264684677124:2.0093183517456 MB
+3/3 LSTM ................................................................ [PASS]
+Completed 0 asserts in 3 tests with 0 failures and 0 errors and 1 warning
+--------------------------------------------------------------------------------
 ```
\ No newline at end of file