Kernel build example (#224)

* Build example kernels.

* Add some sample custom kernel.

* Get the example kernel to compile.

* Add some cuda code.

* More cuda custom op.

* More cuda custom ops.

candle-core/src/cuda_backend.rs

@@ -771,6 +771,50 @@ pub struct CudaStorage {
     device: CudaDevice,
 }
 
+pub trait CudaDType: Sized {
+    fn as_cuda_slice(s: &CudaStorage) -> Result<&CudaSlice<Self>>;
+    fn wrap_cuda_slice(s: CudaSlice<Self>, dev: CudaDevice) -> CudaStorage;
+}
+
+macro_rules! cuda_dtype {
+    ($ty:ty, $dtype:ident) => {
+        impl CudaDType for $ty {
+            fn as_cuda_slice(s: &CudaStorage) -> Result<&CudaSlice<Self>> {
+                match &s.slice {
+                    CudaStorageSlice::$dtype(data) => Ok(&data),
+                    _ => Err(crate::Error::UnexpectedDType {
+                        expected: DType::$dtype,
+                        got: s.dtype(),
+                        msg: "unexpected dtype",
+                    }
+                    .bt()),
+                }
+            }
+
+            fn wrap_cuda_slice(slice: CudaSlice<Self>, device: CudaDevice) -> CudaStorage {
+                let slice = CudaStorageSlice::$dtype(slice);
+                CudaStorage { slice, device }
+            }
+        }
+    };
+}
+cuda_dtype!(u8, U8);
+cuda_dtype!(u32, U32);
+cuda_dtype!(f16, F16);
+cuda_dtype!(bf16, BF16);
+cuda_dtype!(f32, F32);
+cuda_dtype!(f64, F64);
+
+impl CudaStorage {
+    pub fn wrap_cuda_slice<T: CudaDType>(slice: CudaSlice<T>, device: CudaDevice) -> CudaStorage {
+        T::wrap_cuda_slice(slice, device)
+    }
+
+    pub fn as_cuda_slice<T: CudaDType>(&self) -> Result<&CudaSlice<T>> {
+        T::as_cuda_slice(self)
+    }
+}
+
 fn gemm_config<T>(
     alpha: T,
     beta: T,