RandFromRanges

RandFromRanges.jl

import Base: start, next, done, length
type RandFromRangeDown
    k::Int
    mask::Int
end
RandFromRangeDown(k) = RandFromRangeDown(k,2^16-1)
_rnd(::RandFromRangeDown) =  Base.Random.rand_ui52_raw(Base.Random.GLOBAL_RNG)

mm(n,k) = div(n,k)*k
function start(rfr::RandFromRangeDown) 
    d = div(rfr.mask+1,rfr.k)
    rfr.k, d*rfr.k, d
end
length(rfr::RandFromRangeDown) = rfr.k-1

function next(rfr::RandFromRangeDown, state)
    i, j, d = state
    mask = rfr.mask
    while j+i  <= mask + 1
        j = j + i
        d = d + 1
    end
    x = _rnd(rfr) & mask
    while x >= j
        x = _rnd(rfr) & mask
    end
    Int(1 + x % i), (i-1, j-d,d)
end
done(rfr::RandFromRangeDown, state) = state[1] == 1