Function cast_bases_mut 

pub fn cast_bases_mut<FSub, P>(
    packed: &mut [P],
) -> &mut [PackedSubfield<P, FSub>] 
where
    FSub: BinaryField,
    P: PackedField<Scalar: ExtensionField<FSub>> + UnderlierView,
    PackedSubfield<P, FSub>: PackedField<Scalar = FSub>,

Reads a slice of packed extension field elements in place as packed subfield elements.