Method log

dnn/include/megdnn/dtype/half.hpp:1232–1238

			/// \param arg function argument
			/// \return function value stored in single-preicision
            MEGDNN_HOST MEGDNN_DEVICE static expr log(float arg) {
#if defined(__CUDA_ARCH__)
                return expr(logf(arg));
#else
                return expr(std::log(arg));
#endif
            }

			/// Common logarithm implementation.
			/// \param arg function argument