rust-ndarray · bluss · Mar 12, 2021 · Jan 20, 2021 · Jan 23, 2021 · Jan 23, 2021
diff --git a/src/data_traits.rs b/src/data_traits.rs
@@ -16,9 +16,7 @@ use std::ptr::NonNull;
 use alloc::sync::Arc;
 use alloc::vec::Vec;
 
-use crate::{
-    ArrayBase, CowRepr, Dimension, OwnedArcRepr, OwnedRepr, RawViewRepr, ViewRepr,
-};
+use crate::{ArrayBase, CowRepr, Dimension, OwnedArcRepr, OwnedRepr, RawViewRepr, ViewRepr};
 
 /// Array representation trait.
 ///
@@ -414,7 +412,6 @@ pub unsafe trait DataOwned: Data {
     /// Corresponding owned data with MaybeUninit elements
     type MaybeUninit: DataOwned<Elem = MaybeUninit<Self::Elem>>
         + RawDataSubst<Self::Elem, Output=Self>;
-
     #[doc(hidden)]
     fn new(elements: Vec<Self::Elem>) -> Self;
 
@@ -440,6 +437,7 @@ unsafe impl<A> DataOwned for OwnedRepr<A> {
     fn new(elements: Vec<A>) -> Self {
         OwnedRepr::from(elements)
     }
+
     fn into_shared(self) -> OwnedArcRepr<A> {
         OwnedArcRepr(Arc::new(self))
     }
@@ -622,3 +620,4 @@ impl<'a, A: 'a, B: 'a> RawDataSubst<B> for ViewRepr<&'a mut A> {
         ViewRepr::new()
     }
 }
+
diff --git a/src/dimension/broadcast.rs b/src/dimension/broadcast.rs
@@ -0,0 +1,143 @@
+use crate::error::*;
+use crate::{Dimension, Ix0, Ix1, Ix2, Ix3, Ix4, Ix5, Ix6, IxDyn};
+
+/// Calculate the common shape for a pair of array shapes, that they can be broadcasted
+/// to. Return an error if the shapes are not compatible.
+///
+/// Uses the [NumPy broadcasting rules]
+//  (https://docs.scipy.org/doc/numpy/user/basics.broadcasting.html#general-broadcasting-rules).
+pub(crate) fn co_broadcast<D1, D2, Output>(shape1: &D1, shape2: &D2) -> Result<Output, ShapeError>
+where
+    D1: Dimension,
+    D2: Dimension,
+    Output: Dimension,
+{
+    let (k, overflow) = shape1.ndim().overflowing_sub(shape2.ndim());
+    // Swap the order if d2 is longer.
+    if overflow {
+        return co_broadcast::<D2, D1, Output>(shape2, shape1);
+    }
+    // The output should be the same length as shape1.
+    let mut out = Output::zeros(shape1.ndim());
+    for (out, s) in izip!(out.slice_mut(), shape1.slice()) {
+        *out = *s;
+    }
+    for (out, s2) in izip!(&mut out.slice_mut()[k..], shape2.slice()) {
+        if *out != *s2 {
+            if *out == 1 {
+                *out = *s2
+            } else if *s2 != 1 {
+                return Err(from_kind(ErrorKind::IncompatibleShape));
+            }
+        }
+    }
+    Ok(out)
+}
+
+pub trait DimMax<Other: Dimension> {
+    /// The resulting dimension type after broadcasting.
+    type Output: Dimension;
+}
+
+/// Dimensions of the same type remain unchanged when co_broadcast.
+/// So you can directly use D as the resulting type.
+/// (Instead of <D as DimMax<D>>::BroadcastOutput)
+impl<D: Dimension> DimMax<D> for D {
+    type Output = D;
+}
+
+macro_rules! impl_broadcast_distinct_fixed {
+    ($smaller:ty, $larger:ty) => {
+        impl DimMax<$larger> for $smaller {
+            type Output = $larger;
+        }
+
+        impl DimMax<$smaller> for $larger {
+            type Output = $larger;
+        }
+    };
+}
+
+impl_broadcast_distinct_fixed!(Ix0, Ix1);
+impl_broadcast_distinct_fixed!(Ix0, Ix2);
+impl_broadcast_distinct_fixed!(Ix0, Ix3);
+impl_broadcast_distinct_fixed!(Ix0, Ix4);
+impl_broadcast_distinct_fixed!(Ix0, Ix5);
+impl_broadcast_distinct_fixed!(Ix0, Ix6);
+impl_broadcast_distinct_fixed!(Ix1, Ix2);
+impl_broadcast_distinct_fixed!(Ix1, Ix3);
+impl_broadcast_distinct_fixed!(Ix1, Ix4);
+impl_broadcast_distinct_fixed!(Ix1, Ix5);
+impl_broadcast_distinct_fixed!(Ix1, Ix6);
+impl_broadcast_distinct_fixed!(Ix2, Ix3);
+impl_broadcast_distinct_fixed!(Ix2, Ix4);
+impl_broadcast_distinct_fixed!(Ix2, Ix5);
+impl_broadcast_distinct_fixed!(Ix2, Ix6);
+impl_broadcast_distinct_fixed!(Ix3, Ix4);
+impl_broadcast_distinct_fixed!(Ix3, Ix5);
+impl_broadcast_distinct_fixed!(Ix3, Ix6);
+impl_broadcast_distinct_fixed!(Ix4, Ix5);
+impl_broadcast_distinct_fixed!(Ix4, Ix6);
+impl_broadcast_distinct_fixed!(Ix5, Ix6);
+impl_broadcast_distinct_fixed!(Ix0, IxDyn);
+impl_broadcast_distinct_fixed!(Ix1, IxDyn);
+impl_broadcast_distinct_fixed!(Ix2, IxDyn);
+impl_broadcast_distinct_fixed!(Ix3, IxDyn);
+impl_broadcast_distinct_fixed!(Ix4, IxDyn);
+impl_broadcast_distinct_fixed!(Ix5, IxDyn);
+impl_broadcast_distinct_fixed!(Ix6, IxDyn);
+
+
+#[cfg(test)]
+#[cfg(feature = "std")]
+mod tests {
+    use super::co_broadcast;
+    use crate::{Dimension, Dim, DimMax, ShapeError, Ix0, IxDynImpl, ErrorKind};
+
+    #[test]
+    fn test_broadcast_shape() {
+        fn test_co<D1, D2>(
+            d1: &D1,
+            d2: &D2,
+            r: Result<<D1 as DimMax<D2>>::Output, ShapeError>,
+        ) where
+            D1: Dimension + DimMax<D2>,
+            D2: Dimension,
+        {
+            let d = co_broadcast::<D1, D2, <D1 as DimMax<D2>>::Output>(&d1, d2);
+            assert_eq!(d, r);
+        }
+        test_co(&Dim([2, 3]), &Dim([4, 1, 3]), Ok(Dim([4, 2, 3])));
+        test_co(
+            &Dim([1, 2, 2]),
+            &Dim([1, 3, 4]),
+            Err(ShapeError::from_kind(ErrorKind::IncompatibleShape)),
+        );
+        test_co(&Dim([3, 4, 5]), &Ix0(), Ok(Dim([3, 4, 5])));
+        let v = vec![1, 2, 3, 4, 5, 6, 7];
+        test_co(
+            &Dim(vec![1, 1, 3, 1, 5, 1, 7]),
+            &Dim([2, 1, 4, 1, 6, 1]),
+            Ok(Dim(IxDynImpl::from(v.as_slice()))),
+        );
+        let d = Dim([1, 2, 1, 3]);
+        test_co(&d, &d, Ok(d));
+        test_co(
+            &Dim([2, 1, 2]).into_dyn(),
+            &Dim(0),
+            Err(ShapeError::from_kind(ErrorKind::IncompatibleShape)),
+        );
+        test_co(
+            &Dim([2, 1, 1]),
+            &Dim([0, 0, 1, 3, 4]),
+            Ok(Dim([0, 0, 2, 3, 4])),
+        );
+        test_co(&Dim([0]), &Dim([0, 0, 0]), Ok(Dim([0, 0, 0])));
+        test_co(&Dim(1), &Dim([1, 0, 0]), Ok(Dim([1, 0, 0])));
+        test_co(
+            &Dim([1, 3, 0, 1, 1]),
+            &Dim([1, 2, 3, 1]),
+            Err(ShapeError::from_kind(ErrorKind::IncompatibleShape)),
+        );
+    }
+}
diff --git a/src/dimension/dimension_trait.rs b/src/dimension/dimension_trait.rs
@@ -15,7 +15,7 @@ use super::axes_of;
 use super::conversion::Convert;
 use super::{stride_offset, stride_offset_checked};
 use crate::itertools::{enumerate, zip};
-use crate::Axis;
+use crate::{Axis, DimMax};
 use crate::IntoDimension;
 use crate::RemoveAxis;
 use crate::{ArrayView1, ArrayViewMut1};
@@ -46,6 +46,11 @@ pub trait Dimension:
     + MulAssign
     + for<'x> MulAssign<&'x Self>
     + MulAssign<usize>
+    + DimMax<Ix0, Output=Self>
+    + DimMax<Self, Output=Self>
+    + DimMax<IxDyn, Output=IxDyn>
+    + DimMax<<Self as Dimension>::Smaller, Output=Self>
+    + DimMax<<Self as Dimension>::Larger, Output=<Self as Dimension>::Larger>
 {
     /// For fixed-size dimension representations (e.g. `Ix2`), this should be
     /// `Some(ndim)`, and for variable-size dimension representations (e.g.

diff --git a/src/dimension/mod.rs b/src/dimension/mod.rs
@@ -12,6 +12,7 @@ use num_integer::div_floor;
 
 pub use self::axes::{axes_of, Axes, AxisDescription};
 pub use self::axis::Axis;
+pub use self::broadcast::DimMax;
 pub use self::conversion::IntoDimension;
 pub use self::dim::*;
 pub use self::dimension_trait::Dimension;
@@ -28,6 +29,7 @@ use std::mem;
 mod macros;
 mod axes;
 mod axis;
+pub(crate) mod broadcast;
 mod conversion;
 pub mod dim;
 mod dimension_trait;

diff --git a/src/impl_methods.rs b/src/impl_methods.rs
@@ -14,14 +14,15 @@ use rawpointer::PointerExt;
 
 use crate::imp_prelude::*;
 
-use crate::arraytraits;
+use crate::{arraytraits, DimMax};
 use crate::dimension;
 use crate::dimension::IntoDimension;
 use crate::dimension::{
     abs_index, axes_of, do_slice, merge_axes, move_min_stride_axis_to_last,
     offset_from_ptr_to_memory, size_of_shape_checked, stride_offset, Axes,
 };
-use crate::error::{self, ErrorKind, ShapeError};
+use crate::dimension::broadcast::co_broadcast;
+use crate::error::{self, ErrorKind, ShapeError, from_kind};
 use crate::math_cell::MathCell;
 use crate::itertools::zip;
 use crate::zip::Zip;
@@ -1766,6 +1767,28 @@ where
         unsafe { Some(ArrayView::new(self.ptr, dim, broadcast_strides)) }
     }
 
+    /// For two arrays or views, find their common shape if possible and
+    /// broadcast them as array views into that shape.
+    ///
+    /// Return `ShapeError` if their shapes can not be broadcast together.
+    #[allow(clippy::type_complexity)]
+    pub(crate) fn broadcast_with<'a, 'b, B, S2, E>(&'a self, other: &'b ArrayBase<S2, E>) ->
+        Result<(ArrayView<'a, A, DimMaxOf<D, E>>, ArrayView<'b, B, DimMaxOf<D, E>>), ShapeError>
+    where
+        S: Data<Elem=A>,
+        S2: Data<Elem=B>,
+        D: Dimension + DimMax<E>,
+        E: Dimension,
+    {
+        let shape = co_broadcast::<D, E, <D as DimMax<E>>::Output>(&self.dim, &other.dim)?;
+        if let Some(view1) = self.broadcast(shape.clone()) {
+            if let Some(view2) = other.broadcast(shape) {
+                return Ok((view1, view2));
+            }
+        }
+        Err(from_kind(ErrorKind::IncompatibleShape))
+    }
+
     /// Swap axes `ax` and `bx`.
     ///
     /// This does not move any data, it just adjusts the array’s dimensions
@@ -2013,7 +2036,7 @@ where
         self.map_inplace(move |elt| *elt = x.clone());
     }
 
-    fn zip_mut_with_same_shape<B, S2, E, F>(&mut self, rhs: &ArrayBase<S2, E>, mut f: F)
+    pub(crate) fn zip_mut_with_same_shape<B, S2, E, F>(&mut self, rhs: &ArrayBase<S2, E>, mut f: F)
     where
         S: DataMut,
         S2: Data<Elem = B>,
@@ -2443,3 +2466,5 @@ unsafe fn unlimited_transmute<A, B>(data: A) -> B {
     let old_data = ManuallyDrop::new(data);
     (&*old_data as *const A as *const B).read()
 }
+
+type DimMaxOf<A, B> = <A as DimMax<B>>::Output;