added THEANO_FLAGS=nvcc.fastmath (THEANO_FLAGS=fastmath as shortcut). Will add…

theano/config.py

@@ -9,6 +9,7 @@ default_={
 'tensor_opt.local_elemwise_fusion':False,
 'lib.amdlibm':False,
 'op.set_flops':False,#currently used only in ConvOp. The profile mode will print the flops/s for the op.
+'nvcc.fastmath':False,
 }
 
 #default value taked from env variable

theano/sandbox/cuda/type.py

@@ -261,11 +261,17 @@ class CudaNdarrayType(Type):
 
     def c_code_cache_version(self):
         #return ()
+        #no need to put nvcc.fastmath in the tuple as the c_compile_args is put in the key.
         return (2,) # with assertion about refcounts
 
     def c_compiler(self):
         return nvcc_module_compile_str
 
+    def c_compile_args(self):
+        ret = []
+        if config.config.getboolean('nvcc.fastmath'):
+            ret.append('-use_fast_math')
+        return ret
 
 # THIS WORKS
 # But CudaNdarray instances don't compare equal to one another, and what about __hash__ ?