Disable C code for all Elemwise that interact with float16

theano/scalar/basic.py

@@ -1982,8 +1982,6 @@ class Cast(UnaryScalarOp):
     def c_code(self, node, name, inputs, outputs, sub):
         (x,) = inputs
         (z,) = outputs
-        if node.inputs[0].dtype == 'float16' or node.outputs[0] == 'float16':
-            raise NotImplementedError("C code doesn't work for float16")
         return "%s = (%s)%s;" % (z, node.outputs[0].type.dtype_specs()[1], x)
 
     def grad(self, inputs, gout):
@@ -3302,14 +3300,19 @@ class Composite(ScalarOp):
                 + zip(self.fgraph.outputs,
                     ["%%(o%i)s" % i for i in xrange(len(self.fgraph.outputs))]))
 
-        for orphan in self.fgraph.variables:  # fgraph.orphans:
-            if orphan.owner is None and orphan not in self.fgraph.inputs:
-                if isinstance(orphan, Constant):
-                    subd[orphan] = orphan.type.c_literal(orphan.data)
+        for var in self.fgraph.variables:
+            if var.owner is None and var not in self.fgraph.inputs:
+                # This is an orphan
+                if isinstance(var, Constant):
+                    subd[var] = var.type.c_literal(var.data)
                 else:
                     raise ValueError(
                         "All orphans in the fgraph to Composite must"
                         " be Constant instances.")
+            elif any(i.dtype == 'float16' for i in var.owner.inputs or
+                     o.dtype == 'float16' for o in var.owner.outputs):
+                # flag for elemwise ops to check.
+                self.inner_float16 = True
 
         _c_code = "{\n"
         self.nodenames = ["%(nodename)s_" + ('subnode%i' % j)

theano/tensor/elemwise.py

@@ -1171,6 +1171,12 @@ class Elemwise(OpenMPOp):
         return decl, checks, alloc, loop
 
     def c_code(self, node, nodename, inames, onames, sub):
+        if any(i.dtype == 'float16' for i in node.inputs or
+               o.dtype == 'float16' for o in node.inputs or
+               # This is for Composite
+               getattr(self.scalar_op, 'inner_float16', False)):
+            # Disable C code for float16 vars
+            super(Elemwise, self).c_code(node, nodename, inames, onames, sub)
         code = "\n".join(self._c_all(node, nodename, inames, onames, sub))
         return code