avoid ind2sub in view with Block{1} (#268)

Author: jishnub

src/abstractblockarray.jl

@@ -133,7 +133,10 @@ end
 
 viewblock(block_arr, block) = Base.invoke(view, Tuple{AbstractArray, Any}, block_arr, block)
 @inline Base.view(block_arr::AbstractBlockArray{<:Any,N}, block::Block{N}) where N = viewblock(block_arr, block)
-@inline Base.view(block_arr::AbstractBlockArray{<:Any,N}, block::Block{1}) where N = view(block_arr, Block(Base._ind2sub(map(Base.OneTo, blocksize(block_arr)), Int(block))...))
+@inline function Base.view(block_arr::AbstractBlockArray, block::Block{1})
+    blkind = BlockRange(blocksize(block_arr))[Int(block)]
+    view(block_arr, blkind)
+end
 @inline Base.view(block_arr::AbstractBlockVector, block::Block{1}) = viewblock(block_arr, block)
 @inline @propagate_inbounds Base.view(block_arr::AbstractBlockArray, block::Block{1}...) = view(block_arr, Block(block))
 

src/blockindices.jl

@@ -325,6 +325,10 @@ BlockRange(inds::NTuple{N,AbstractUnitRange{Int}}) where {N} =
 BlockRange(inds::Vararg{AbstractUnitRange{Int},N}) where {N} =
     BlockRange(inds)
 
+BlockRange() = BlockRange(())
+BlockRange(sizes::Tuple{Int, Vararg{Int}}) = BlockRange(map(Base.OneTo, sizes))
+BlockRange(sizes::Vararg{Int}) = BlockRange(sizes)
+
 (:)(start::Block{1}, stop::Block{1}) = BlockRange((first(start.n):first(stop.n),))
 (:)(start::Block, stop::Block) = throw(ArgumentError("Use `BlockRange` to construct a cartesian range of blocks"))
 Base.BroadcastStyle(::Type{<:BlockRange{1}}) = DefaultArrayStyle{1}()

test/test_blockviews.jl

@@ -44,7 +44,7 @@ bview(a, b) = Base.invoke(view, Tuple{AbstractArray,Any}, a, b)
         V[1,1] = -1
         @test A[2,8] == -1
         @test A[Block(4)] == A[Block(1),Block(2)]
-        @test_throws BlockBoundsError A[Block(10)]
+        @test_throws BoundsError A[Block(10)]
 
         V = view(A, Block(3, 2))
         @test size(V) == (3, 4)