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-examples/examples/custom-ops/main.rs

@@ -0,0 +1,65 @@
+#![allow(dead_code)]
+#![allow(unused)]
+
+#[cfg(feature = "mkl")]
+extern crate intel_mkl_src;
+
+use clap::Parser;
+
+use candle::backend::BackendStorage;
+use candle::cpu_backend;
+use candle::{CpuStorage, CustomOp1, DType, Device, Error, Layout, Result, Shape, Tensor};
+
+#[derive(Parser, Debug)]
+#[command(author, version, about, long_about = None)]
+struct Args {
+    /// Run on CPU rather than on GPU.
+    #[arg(long)]
+    cpu: bool,
+}
+
+struct LayerNorm;
+
+impl CustomOp1 for LayerNorm {
+    fn name(&self) -> &'static str {
+        "layer-norm"
+    }
+
+    fn cpu_fwd(&self, s: &CpuStorage, l: &Layout) -> Result<(CpuStorage, Shape)> {
+        let s = s.as_slice::<f32>()?;
+        let _s = match l.contiguous_offsets() {
+            None => Err(Error::Wrapped("input has to be contiguous".into()))?,
+            Some((o1, o2)) => &s[o1..o2],
+        };
+        todo!()
+    }
+
+    #[cfg(feature = "cuda")]
+    fn cuda_fwd(
+        &self,
+        s: &candle::CudaStorage,
+        l: &Layout,
+    ) -> Result<(candle::CudaStorage, Shape)> {
+        let device = s.device().clone();
+        let s = s.as_cuda_slice::<f32>()?;
+        let s = match l.contiguous_offsets() {
+            None => Err(Error::Wrapped("input has to be contiguous".into()))?,
+            Some((o1, o2)) => s, // TODO: slice with o1 and o2
+        };
+        let s: std::result::Result<_, candle::cuda_backend::CudaError> =
+            s.try_clone().map_err(|v| v.into());
+        let s = s?;
+        let s = candle::CudaStorage::wrap_cuda_slice(s, device);
+        Ok((s, l.shape().clone()))
+    }
+}
+
+fn main() -> anyhow::Result<()> {
+    let args = Args::parse();
+    let device = candle_examples::device(args.cpu)?;
+    let t = Tensor::arange(0f32, 14f32, &device)?.reshape((2, 7))?;
+    println!("{t}");
+    let t = t.custom_op1(LayerNorm)?;
+    println!("{t}");
+    Ok(())
+}