Add support for 'log' mode in GpuDnnSoftmax

theano/sandbox/cuda/dnn.py

@@ -1313,8 +1313,9 @@ class GpuDnnSoftmaxBase(DnnBase):
     Op for the cuDNN Softmax.
 
     :param tensor_format: Whether the data format is 'bc01' or 'b01c'.
-    :param algo: 'fast' or 'accurate' indicating whether computations should be
-        optimized for speed or accuracy respectively.
+    :param algo: 'fast', 'accurate' or 'log' indicating whether, respectively,
+        computations should be optimized for speed, for accuracy, or if CuDNN
+        should rather compute the log-softmax instead.
     :param mode: 'instance' or 'channel' indicating whether the softmax should
         be computed per image across 'c01' or per spatial location '01' per
         image across 'c'.
@@ -1327,7 +1328,7 @@ class GpuDnnSoftmaxBase(DnnBase):
         DnnBase.__init__(self)
         self.tensor_format = tensor_format
 
-        assert(algo in ('fast', 'accurate'))
+        assert(algo in ('fast', 'accurate', 'log'))
         self.algo = algo
 
         assert(mode in ('instance', 'channel'))
@@ -1401,6 +1402,8 @@ cudnnStatus_t err%(name)s;
 
         if self.algo == 'fast':
             algo = 1
+        elif self.algo == "log":
+            algo = 2
         else:
             algo = 0
 
@@ -1414,6 +1417,8 @@ if (%(tensor_format)d == 1)
 cudnnSoftmaxAlgorithm_t algo%(name)s = CUDNN_SOFTMAX_ACCURATE;
 if (%(algo)d == 1)
   algo%(name)s = CUDNN_SOFTMAX_FAST;
+if (%(algo)d == 2)
+  algo%(name)s = CUDNN_SOFTMAX_LOG;
 
 cudnnSoftmaxMode_t mode%(name)s = CUDNN_SOFTMAX_MODE_CHANNEL;
 if (%(mode)d == 1)