1 files changed, 140 insertions, 0 deletions
diff --git a/candle-core/src/layout.rs b/candle-core/src/layout.rs
new file mode 100644
index 00000000..3f629d50
--- /dev/null
+++ b/candle-core/src/layout.rs
@@ -0,0 +1,140 @@
+use crate::{Error, Result, Shape};
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub struct Layout {
+    shape: Shape,
+    // The strides are given in number of elements and not in bytes.
+    stride: Vec<usize>,
+    start_offset: usize,
+}
+
+impl Layout {
+    pub fn contiguous_with_offset<S: Into<Shape>>(shape: S, start_offset: usize) -> Self {
+        let shape = shape.into();
+        let stride = shape.stride_contiguous();
+        Self {
+            shape,
+            stride,
+            start_offset,
+        }
+    }
+
+    pub fn contiguous<S: Into<Shape>>(shape: S) -> Self {
+        Self::contiguous_with_offset(shape, 0)
+    }
+
+    pub fn dims(&self) -> &[usize] {
+        self.shape.dims()
+    }
+
+    pub fn shape(&self) -> &Shape {
+        &self.shape
+    }
+
+    pub fn stride(&self) -> &[usize] {
+        &self.stride
+    }
+
+    pub fn start_offset(&self) -> usize {
+        self.start_offset
+    }
+
+    /// Returns the appropriate start and stop offset if the data is stored in a C
+    /// contiguous (aka row major) way.
+    pub fn contiguous_offsets(&self) -> Option<(usize, usize)> {
+        if self.is_contiguous() {
+            let start_o = self.start_offset;
+            Some((start_o, start_o + self.shape.elem_count()))
+        } else {
+            None
+        }
+    }
+
+    /// Returns true if the data is stored in a C contiguous (aka row major) way.
+    pub fn is_contiguous(&self) -> bool {
+        self.shape.is_contiguous(&self.stride)
+    }
+
+    /// Returns true if the data is stored in a Fortran contiguous (aka column major) way.
+    pub fn is_fortran_contiguous(&self) -> bool {
+        self.shape.is_fortran_contiguous(&self.stride)
+    }
+
+    pub(crate) fn narrow(&self, dim: usize, start: usize, length: usize) -> Result<Self> {
+        let dims = self.shape().dims();
+        if dim >= dims.len() {
+            Err(Error::UnexpectedNumberOfDims {
+                expected: dim + 1,
+                got: dims.len(),
+                shape: self.shape().clone(),
+            })?
+        }
+        if start + length > dims[dim] {
+            todo!("add a proper error: out of bounds for narrow {dim} {start} {length} {dims:?}")
+        }
+        let mut dims = dims.to_vec();
+        dims[dim] = length;
+        Ok(Self {
+            shape: Shape::from(dims),
+            stride: self.stride.clone(),
+            start_offset: self.start_offset + self.stride[dim] * start,
+        })
+    }
+
+    pub(crate) fn transpose(&self, dim1: usize, dim2: usize) -> Result<Self> {
+        let rank = self.shape.rank();
+        if rank <= dim1 || rank <= dim2 {
+            return Err(Error::UnexpectedNumberOfDims {
+                expected: usize::max(dim1, dim2),
+                got: rank,
+                shape: self.shape().clone(),
+            });
+        }
+        let mut stride = self.stride().to_vec();
+        let mut dims = self.shape().dims().to_vec();
+        dims.swap(dim1, dim2);
+        stride.swap(dim1, dim2);
+        Ok(Self {
+            shape: Shape::from(dims),
+            stride,
+            start_offset: self.start_offset,
+        })
+    }
+
+    pub fn broadcast_as<S: Into<Shape>>(&self, shape: S) -> Result<Self> {
+        let shape = shape.into();
+        if shape.rank() < self.shape().rank() {
+            Err(Error::BroadcastIncompatibleShapes {
+                src_shape: self.shape().clone(),
+                dst_shape: shape.clone(),
+            })?
+        }
+        let added_dims = shape.rank() - self.shape().rank();
+        let mut stride = vec![0; added_dims];
+        for (&dst_dim, (&src_dim, &src_stride)) in shape.dims()[added_dims..]
+            .iter()
+            .zip(self.dims().iter().zip(self.stride()))
+        {
+            let s = if dst_dim == src_dim {
+                src_stride
+            } else if src_dim != 1 {
+                return Err(Error::BroadcastIncompatibleShapes {
+                    src_shape: self.shape().clone(),
+                    dst_shape: shape,
+                });
+            } else {
+                0
+            };
+            stride.push(s)
+        }
+        Ok(Self {
+            shape,
+            stride,
+            start_offset: self.start_offset,
+        })
+    }
+
+    pub(crate) fn strided_index(&self) -> crate::StridedIndex {
+        crate::StridedIndex::new(self)
+    }
+}