Fix views of arrays that do not start at the beginning of their memory

ext/StridedViewsPtrArraysExt.jl

@@ -3,6 +3,6 @@ module StridedViewsPtrArraysExt
 using StridedViews
 using PtrArrays
 
-StridedViews._normalizeparent(A::PtrArray) = PtrArray(A.ptr, length(A))
+StridedViews._normalizeparent(A::PtrArray, offset::Int) = PtrArray(A.ptr, length(A)), offset
 
 end

src/auxiliary.jl

@@ -46,12 +46,14 @@ function _normalizestrides(size::Dims{N}, strides::Dims{N}) where {N}
 end
 
 # 'Normalize' the layout of a DenseArray, in order to reduce the number of required
-# specializations in functions.
-@inline _normalizeparent(A) = A
+# specializations in functions. The offset is adjusted to the start of `A` in the
+# normalized parent.
+@inline _normalizeparent(A, offset::Int) = A, offset
 @static if isdefined(Core, :Memory)
-    @inline _normalizeparent(A::Array) = A.ref.mem
+    @inline _normalizeparent(A::Array, offset::Int) =
+        A.ref.mem, offset + Base.memoryrefoffset(A.ref) - 1
 else
-    @inline _normalizeparent(A::Array) = reshape(A, length(A))
+    @inline _normalizeparent(A::Array, offset::Int) = reshape(A, length(A)), offset
 end
 
 # Auxiliary methods for `sview`

src/stridedview.jl

@@ -51,9 +51,9 @@ function StridedView{T}(
         offset::Int = 0,
         op::F = identity
     ) where {T, N, F}
-    parent′ = _normalizeparent(parent)
+    parent′, offset′ = _normalizeparent(parent, offset)
     strides′ = _normalizestrides(size, strides)
-    return StridedView{T, N, typeof(parent′), F}(parent′, size, strides′, offset, op)
+    return StridedView{T, N, typeof(parent′), F}(parent′, size, strides′, offset′, op)
 end
 
 """

test/runtests.jl

@@ -151,6 +151,19 @@ if !is_buildkite
         @test !isstrided(Diagonal([0.5, 1.0, 1.5]))
     end
 
+    @testset "arrays not starting at the beginning of their memory" begin
+        v = collect(1.0:6.0)
+        popfirst!(v)
+        @test StridedView(v) == v
+        @test pointer(StridedView(v)) == pointer(v)
+        M = reshape(deleteat!(collect(1.0:8.0), 1:2), 2, 3)
+        @test StridedView(M) == M
+        @test StridedView(M)[:, 2:3] == M[:, 2:3]
+        @test sview(M, 2, :) == M[2, :]
+        StridedView(M)[2, 1] = 0
+        @test M[2, 1] == 0
+    end
+
     @testset "transpose and adjoint with vector StridedView" begin
         @testset for T in (Float32, Float64, Complex{Float32}, Complex{Float64})
             A = randn(T, (60,))