Start adding some ops.

src/tensor.rs

@@ -1,4 +1,4 @@
-use crate::{op::Op, storage::Storage, DType, Device, Result, Shape};
+use crate::{op::Op, storage::Storage, DType, Device, Error, Result, Shape};
 use std::sync::Arc;
 
 #[allow(dead_code)]
@@ -45,11 +45,46 @@ impl Tensor {
         Ok(Self(Arc::new(tensor_)))
     }
 
-    pub fn to_scalar<S: crate::WithDType>(&self) -> Result<S> {
-        // TODO: properly use the strides here.
+    pub(crate) fn same_shape_binary_op(&self, rhs: &Self, op: &'static str) -> Result<()> {
+        let lhs = self.shape();
+        let rhs = rhs.shape();
+        if lhs != rhs {
+            Err(Error::ShapeMismatchBinaryOp {
+                lhs: lhs.clone(),
+                rhs: rhs.clone(),
+                op,
+            })
+        } else {
+            Ok(())
+        }
+    }
+
+    pub fn add(&self, rhs: &Self) -> Result<Self> {
+        self.same_shape_binary_op(rhs, "add")?;
         todo!()
     }
 
+    pub fn mul(&self, rhs: &Self) -> Result<Self> {
+        self.same_shape_binary_op(rhs, "mul")?;
+        todo!()
+    }
+
+    pub fn to_scalar<S: crate::WithDType>(&self) -> Result<S> {
+        if self.rank() != 0 {
+            return Err(Error::UnexpectedNumberOfDims {
+                expected: 0,
+                got: self.rank(),
+                shape: self.shape().clone(),
+            });
+        }
+        match &self.0.storage {
+            Storage::Cpu(cpu_storage) => {
+                let data = S::cpu_storage_as_slice(cpu_storage)?;
+                Ok(data[0])
+            }
+        }
+    }
+
     pub fn to_vec1<S: crate::WithDType>(&self) -> Result<Vec<S>> {
         // TODO: properly use the strides here.
         todo!()