Split Mersenne-Twister states between rand() and rand(N>382) #6573
Description
As reported on the dev mailing list, there's some sort of DSFMT state corruption after generating odd-length arrays with more than 382 elements:
julia> srand(0); rand(); x = rand(383);
julia> find(x .== x[end])
2-element Array{Int64,1}:
2
383
julia> find(x .== rand())
1-element Array{Int64,1}:
3
julia> find(x .== rand())
1-element Array{Int64,1}:
4
It looks (to my novice eyes) like rand() (which punts to an implementation in dsfmt.h:266) and rand(n) (implemented in dsfmt.c:182) end up with independent DSFMT states. I'm not sure how or why, but it only seems to get triggered after calling rand(N) with odd N > 382... which is a very specific branch in librandom.jl:120.
Edit: It seems to be much more general than what I stated above. I think rand() and rand(N) are living completely split lives with separate states; N need not be odd to trigger the bug. All that is required is that there's a call to rand() before doing the array generation (In the initial report, it was repeating calls of rand(N) with N odd — which satisfies the call to rand()).
julia> srand(0); rand()
0.8236475079774124
julia> x = rand(384);
julia> find(x .== rand())
1-element Array{Int64,1}:
4