There was some discussion about this issue here. Essentially, when using linear indexing of an array @turbo appears to start indexing the array incorrectly when a offset term is used. An example of this (code and commentary copied directly from the discourse discussion) is below.
julia> H = collect(reshape(1.0:6.0, 3, 2))
3×2 Matrix{Float64}:
1.0 4.0
2.0 5.0
3.0 6.0
julia> su = zeros(3);
julia> for k = 1:1
ind = 0 # LinearIndices((3, 2))[1, 1] - 1
for ij in 1:3
su[ij] += H[ij + ind]
end
end
julia> su
3-element Vector{Float64}:
1.0
2.0
3.0
julia> su = zeros(3);
julia> for k = 1:1
ind = 0
@turbo for ij in 1:3
su[ij] += H[ij + ind]
end
end
julia> su
3-element Vector{Float64}:
6.94274366677856e-310
1.0
2.0
so H is being indexed at 0, 1, 2 instead of 1, 2, 3. The effect doesn’t seem to happen on the left hand expression e.g. su[ij + ind] and doesn’t seem to shift more with more additions e.g. H[ij + ind + ind]. It does it correctly if the index was added to a literal 0 instead of ind or if not added:
julia> su = zeros(3);
julia> for k = 1:1
@turbo for ij in 1:3
su[ij] += H[ij + 0]
end
end
julia> su
3-element Vector{Float64}:
1.0
2.0
3.0
julia> su = zeros(3);
julia> for k = 1:1
@turbo for ij in 1:3
su[ij] += H[ij]
end
end
julia> su
3-element Vector{Float64}:
1.0
2.0
3.0
There was some discussion about this issue here. Essentially, when using linear indexing of an array
@turbo
appears to start indexing the array incorrectly when a offset term is used. An example of this (code and commentary copied directly from the discourse discussion) is below.so
H
is being indexed at 0, 1, 2 instead of 1, 2, 3. The effect doesn’t seem to happen on the left hand expression e.g.su[ij + ind]
and doesn’t seem to shift more with more additions e.g.H[ij + ind + ind]
. It does it correctly if the index was added to a literal 0 instead ofind
or if not added: