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Try implementing N-dimensional indexing for fast linear SubArrays #30266

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Dec 17, 2018
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Try implementing N-dimensional indexing for fast linear SubArrays #30266

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32 changes: 30 additions & 2 deletions base/subarray.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -222,13 +222,14 @@ end

# In general, we simply re-index the parent indices by the provided ones
SlowSubArray{T,N,P,I} = SubArray{T,N,P,I,false}
function getindex(V::SlowSubArray{T,N}, I::Vararg{Int,N}) where {T,N}
function getindex(V::SubArray{T,N}, I::Vararg{Int,N}) where {T,N}
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Brilliant optimization --- just remove the word "slow"! 😄

@_inline_meta
@boundscheck checkbounds(V, I...)
@inbounds r = V.parent[reindex(V, V.indices, I)...]
r
end

# But SubArrays with fast linear indexing pre-compute a stride and offset
FastSubArray{T,N,P,I} = SubArray{T,N,P,I,true}
function getindex(V::FastSubArray, i::Int)
@_inline_meta
Expand All @@ -246,8 +247,23 @@ function getindex(V::FastContiguousSubArray, i::Int)
@inbounds r = V.parent[V.offset1 + i]
r
end
# For vector views with linear indexing, we disambiguate to favor the stride/offset
# computation as that'll generally be faster than (or just as fast as) re-indexing into a range.
function getindex(V::FastSubArray{<:Any, 1}, i::Int)
@_inline_meta
@boundscheck checkbounds(V, i)
@inbounds r = V.parent[V.offset1 + V.stride1*i]
r
end
function getindex(V::FastContiguousSubArray{<:Any, 1}, i::Int)
@_inline_meta
@boundscheck checkbounds(V, i)
@inbounds r = V.parent[V.offset1 + i]
r
end

function setindex!(V::SlowSubArray{T,N}, x, I::Vararg{Int,N}) where {T,N}
# Indexed assignment follows the same pattern as `getindex` above
function setindex!(V::SubArray{T,N}, x, I::Vararg{Int,N}) where {T,N}
@_inline_meta
@boundscheck checkbounds(V, I...)
@inbounds V.parent[reindex(V, V.indices, I)...] = x
Expand All @@ -265,6 +281,18 @@ function setindex!(V::FastContiguousSubArray, x, i::Int)
@inbounds V.parent[V.offset1 + i] = x
V
end
function setindex!(V::FastSubArray{<:Any, 1}, x, i::Int)
@_inline_meta
@boundscheck checkbounds(V, i)
@inbounds V.parent[V.offset1 + V.stride1*i] = x
V
end
function setindex!(V::FastContiguousSubArray{<:Any, 1}, x, i::Int)
@_inline_meta
@boundscheck checkbounds(V, i)
@inbounds V.parent[V.offset1 + i] = x
V
end

IndexStyle(::Type{<:FastSubArray}) = IndexLinear()
IndexStyle(::Type{<:SubArray}) = IndexCartesian()
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