Adding some doc + Extended stack to work with extra final dimensions.

candle-core/src/shape.rs

@@ -185,6 +185,7 @@ impl Shape {
 
 pub trait Dim {
     fn to_index(&self, shape: &Shape, op: &'static str) -> Result<usize>;
+    fn to_index_plus_one(&self, shape: &Shape, op: &'static str) -> Result<usize>;
 }
 
 impl Dim for usize {
@@ -200,6 +201,19 @@ impl Dim for usize {
             Ok(dim)
         }
     }
+
+    fn to_index_plus_one(&self, shape: &Shape, op: &'static str) -> Result<usize> {
+        let dim = *self;
+        if dim > shape.dims().len() {
+            Err(Error::DimOutOfRange {
+                shape: shape.clone(),
+                dim,
+                op,
+            })?
+        } else {
+            Ok(dim)
+        }
+    }
 }
 
 pub enum D {
@@ -220,6 +234,19 @@ impl Dim for D {
             }),
         }
     }
+
+    fn to_index_plus_one(&self, shape: &Shape, op: &'static str) -> Result<usize> {
+        let rank = shape.rank();
+        match self {
+            Self::Minus1 if rank >= 1 => Ok(rank),
+            Self::Minus2 if rank >= 2 => Ok(rank - 1),
+            _ => Err(Error::DimOutOfRange {
+                shape: shape.clone(),
+                dim: 42, // TODO: Have an adequate error
+                op,
+            }),
+        }
+    }
 }
 
 #[cfg(test)]