# This file is a part of Julia. License is MIT: https://julialang.org/license

## RandomDevice


"""
    RandomDevice()

Create a `RandomDevice` RNG object.
Two such objects will always generate different streams of random numbers.
The entropy is obtained from the operating system.
"""
struct RandomDevice <: AbstractRNG; end
RandomDevice(seed::Nothing) = RandomDevice()
seed!(rng::RandomDevice) = rng

rand(rd::RandomDevice, sp::SamplerBoolBitInteger) = Libc.getrandom!(Ref{sp[]}())[]
rand(rd::RandomDevice, ::SamplerType{Bool}) = rand(rd, UInt8) % Bool
function rand!(rd::RandomDevice, A::Array{Bool}, ::SamplerType{Bool})
    Libc.getrandom!(A)
    # we need to mask the result so that only the LSB in each byte can be non-zero
    GC.@preserve A begin
        p = Ptr{UInt8}(pointer(A))
        for i = 1:length(A)
            unsafe_store!(p, unsafe_load(p) & 0x1)
            p += 1
        end
    end
    return A
end
for T in BitInteger_types
    @eval rand!(rd::RandomDevice, A::Array{$T}, ::SamplerType{$T}) = Libc.getrandom!(A)
end

# RandomDevice produces natively UInt64
rng_native_52(::RandomDevice) = UInt64


## MersenneTwister

const MT_CACHE_F = 501 << 1 # number of Float64 in the cache
const MT_CACHE_I = 501 << 4 # number of bytes in the UInt128 cache

@assert dsfmt_get_min_array_size() <= MT_CACHE_F

mutable struct MersenneTwister <: AbstractRNG
    seed::Vector{UInt32}
    state::DSFMT_state
    vals::Vector{Float64}
    ints::Vector{UInt128}
    idxF::Int
    idxI::Int

    # counters for show
    adv::Int64          # state of advance at the DSFMT_state level
    adv_jump::BigInt    # number of skipped Float64 values via randjump
    adv_vals::Int64     # state of advance when vals is filled-up
    adv_ints::Int64     # state of advance when ints is filled-up

    function MersenneTwister(seed, state, vals, ints, idxF, idxI,
                             adv, adv_jump, adv_vals, adv_ints)
        length(vals) == MT_CACHE_F && 0 <= idxF <= MT_CACHE_F ||
            throw(DomainError((length(vals), idxF),
                      "`length(vals)` and `idxF` must be consistent with $MT_CACHE_F"))
        length(ints) == MT_CACHE_I >> 4 && 0 <= idxI <= MT_CACHE_I ||
            throw(DomainError((length(ints), idxI),
                      "`length(ints)` and `idxI` must be consistent with $MT_CACHE_I"))
        new(seed, state, vals, ints, idxF, idxI,
            adv, adv_jump, adv_vals, adv_ints)
    end
end

MersenneTwister(seed::Vector{UInt32}, state::DSFMT_state) =
    MersenneTwister(seed, state,
                    Vector{Float64}(undef, MT_CACHE_F),
                    Vector{UInt128}(undef, MT_CACHE_I >> 4),
                    MT_CACHE_F, 0, 0, 0, -1, -1)

"""
    MersenneTwister(seed)
    MersenneTwister()

Create a `MersenneTwister` RNG object. Different RNG objects can have
their own seeds, which may be useful for generating different streams
of random numbers.
The `seed` may be a non-negative integer or a vector of
`UInt32` integers. If no seed is provided, a randomly generated one
is created (using entropy from the system).
See the [`seed!`](@ref) function for reseeding an already existing
`MersenneTwister` object.


# Examples
```jldoctest
julia> rng = MersenneTwister(1234);

julia> x1 = rand(rng, 2)
2-element Vector{Float64}:
 0.5908446386657102
 0.7667970365022592

julia> rng = MersenneTwister(1234);

julia> x2 = rand(rng, 2)
2-element Vector{Float64}:
 0.5908446386657102
 0.7667970365022592

julia> x1 == x2
true
```
"""
MersenneTwister(seed=nothing) =
    seed!(MersenneTwister(Vector{UInt32}(), DSFMT_state()), seed)


function copy!(dst::MersenneTwister, src::MersenneTwister)
    copyto!(resize!(dst.seed, length(src.seed)), src.seed)
    copy!(dst.state, src.state)
    copyto!(dst.vals, src.vals)
    copyto!(dst.ints, src.ints)
    dst.idxF = src.idxF
    dst.idxI = src.idxI
    dst.adv = src.adv
    dst.adv_jump = src.adv_jump
    dst.adv_vals = src.adv_vals
    dst.adv_ints = src.adv_ints
    dst
end

copy(src::MersenneTwister) =
    MersenneTwister(copy(src.seed), copy(src.state), copy(src.vals), copy(src.ints),
                    src.idxF, src.idxI, src.adv, src.adv_jump, src.adv_vals, src.adv_ints)


==(r1::MersenneTwister, r2::MersenneTwister) =
    r1.seed == r2.seed && r1.state == r2.state &&
    isequal(r1.vals, r2.vals) &&
    isequal(r1.ints, r2.ints) &&
    r1.idxF == r2.idxF && r1.idxI == r2.idxI

hash(r::MersenneTwister, h::UInt) =
    foldr(hash, (r.seed, r.state, r.vals, r.ints, r.idxF, r.idxI); init=h)

function show(io::IO, rng::MersenneTwister)
    # seed
    seed = from_seed(rng.seed)
    seed_str = seed <= typemax(Int) ? string(seed) : "0x" * string(seed, base=16) # DWIM
    if rng.adv_jump == 0 && rng.adv == 0
        return print(io, MersenneTwister, "(", seed_str, ")")
    end
    print(io, MersenneTwister, "(", seed_str, ", (")
    # state
    sep = ", "
    show(io, rng.adv_jump)
    print(io, sep)
    show(io, rng.adv)
    if rng.adv_vals != -1 || rng.adv_ints != -1
        # "(0, 0)" is nicer on the eyes than (-1, 1002)
        s = rng.adv_vals != -1
        print(io, sep)
        show(io, s ? rng.adv_vals : zero(rng.adv_vals))
        print(io, sep)
        show(io, s ? rng.idxF : zero(rng.idxF))
    end
    if rng.adv_ints != -1
        idxI = (length(rng.ints)*16 - rng.idxI) / 8 # 8 represents one Int64
        idxI = Int(idxI) # idxI should always be an integer when using public APIs
        print(io, sep)
        show(io, rng.adv_ints)
        print(io, sep)
        show(io, idxI)
    end
    print(io, "))")
end

### low level API

function reset_caches!(r::MersenneTwister)
    # zeroing the caches makes comparing two MersenneTwister RNGs easier
    fill!(r.vals, 0.0)
    fill!(r.ints, zero(UInt128))
    mt_setempty!(r)
    mt_setempty!(r, UInt128)
    r.adv_vals = -1
    r.adv_ints = -1
    r
end

#### floats

mt_avail(r::MersenneTwister) = MT_CACHE_F - r.idxF
mt_empty(r::MersenneTwister) = r.idxF == MT_CACHE_F
mt_setfull!(r::MersenneTwister) = r.idxF = 0
mt_setempty!(r::MersenneTwister) = r.idxF = MT_CACHE_F
mt_pop!(r::MersenneTwister) = @inbounds return r.vals[r.idxF+=1]

@noinline function gen_rand(r::MersenneTwister)
    r.adv_vals = r.adv
    GC.@preserve r fill_array!(r, pointer(r.vals), length(r.vals), CloseOpen12())
    mt_setfull!(r)
end

reserve_1(r::MersenneTwister) = (mt_empty(r) && gen_rand(r); nothing)
# `reserve` allows one to call `rand_inbounds` n times
# precondition: n <= MT_CACHE_F
reserve(r::MersenneTwister, n::Int) = (mt_avail(r) < n && gen_rand(r); nothing)

#### ints

logsizeof(::Type{<:Union{Bool,Int8,UInt8}}) = 0
logsizeof(::Type{<:Union{Int16,UInt16}}) = 1
logsizeof(::Type{<:Union{Int32,UInt32}}) = 2
logsizeof(::Type{<:Union{Int64,UInt64}}) = 3
logsizeof(::Type{<:Union{Int128,UInt128}}) = 4

idxmask(::Type{<:Union{Bool,Int8,UInt8}}) = 15
idxmask(::Type{<:Union{Int16,UInt16}}) = 7
idxmask(::Type{<:Union{Int32,UInt32}}) = 3
idxmask(::Type{<:Union{Int64,UInt64}}) = 1
idxmask(::Type{<:Union{Int128,UInt128}}) = 0


mt_avail(r::MersenneTwister, ::Type{T}) where {T<:BitInteger} =
    r.idxI >> logsizeof(T)

function mt_setfull!(r::MersenneTwister, ::Type{<:BitInteger})
    r.adv_ints = r.adv
    ints = r.ints

    @assert length(ints) == 501
    # dSFMT natively randomizes 52 out of 64 bits of each UInt64 words,
    # i.e. 12 bits are missing;
    # by generating 5 words == 5*52 == 260 bits, we can fully
    # randomize 4 UInt64 = 256 bits; IOW, at the array level, we must
    # randomize ceil(501*1.25) = 627 UInt128 words (with 2*52 bits each),
    # which we then condense into fully randomized 501 UInt128 words

    len = 501 + 126 # 126 == ceil(501 / 4)
    resize!(ints, len)
    p = pointer(ints) # must be *after* resize!
    GC.@preserve r fill_array!(r, Ptr{Float64}(p), len*2, CloseOpen12_64())

    k = 501
    n = 0
    @inbounds while n != 500
        u = ints[k+=1]
        ints[n+=1] ⊻= u << 48
        ints[n+=1] ⊻= u << 36
        ints[n+=1] ⊻= u << 24
        ints[n+=1] ⊻= u << 12
    end
    @assert k == len - 1
    @inbounds ints[501] ⊻= ints[len] << 48
    resize!(ints, 501)
    r.idxI = MT_CACHE_I
end

mt_setempty!(r::MersenneTwister, ::Type{<:BitInteger}) = r.idxI = 0

function reserve1(r::MersenneTwister, ::Type{T}) where T<:BitInteger
    r.idxI < sizeof(T) && mt_setfull!(r, T)
    nothing
end

function mt_pop!(r::MersenneTwister, ::Type{T}) where T<:BitInteger
    reserve1(r, T)
    r.idxI -= sizeof(T)
    i = r.idxI
    @inbounds x128 = r.ints[1 + i >> 4]
    i128 = (i >> logsizeof(T)) & idxmask(T) # 0-based "indice" in x128
    (x128 >> (i128 * (sizeof(T) << 3))) % T
end

function mt_pop!(r::MersenneTwister, ::Type{T}) where {T<:Union{Int128,UInt128}}
    reserve1(r, T)
    idx = r.idxI >> 4
    r.idxI = idx << 4 - 16
    @inbounds r.ints[idx] % T
end


### seeding

#### make_seed()

# make_seed produces values of type Vector{UInt32}, suitable for MersenneTwister seeding
function make_seed()
    try
        return rand(RandomDevice(), UInt32, 4)
    catch ex
        ex isa IOError || rethrow()
        @warn "Entropy pool not available to seed RNG; using ad-hoc entropy sources."
        return make_seed(Libc.rand())
    end
end

function make_seed(n::Integer)
    n < 0 && throw(DomainError(n, "`n` must be non-negative."))
    seed = UInt32[]
    while true
        push!(seed, n & 0xffffffff)
        n >>= 32
        if n == 0
            return seed
        end
    end
end

# inverse of make_seed(::Integer)
from_seed(a::Vector{UInt32})::BigInt = sum(a[i] * big(2)^(32*(i-1)) for i in 1:length(a))


#### seed!()

function seed!(r::MersenneTwister, seed::Vector{UInt32})
    copyto!(resize!(r.seed, length(seed)), seed)
    dsfmt_init_by_array(r.state, r.seed)
    reset_caches!(r)
    r.adv = 0
    r.adv_jump = 0
    return r
end

seed!(r::MersenneTwister) = seed!(r, make_seed())
seed!(r::MersenneTwister, n::Integer) = seed!(r, make_seed(n))


### Global RNG

struct _GLOBAL_RNG <: AbstractRNG
    global const GLOBAL_RNG = _GLOBAL_RNG.instance
end

# GLOBAL_RNG currently uses TaskLocalRNG
typeof_rng(::_GLOBAL_RNG) = TaskLocalRNG

"""
    default_rng() -> rng

Return the default global random number generator (RNG).

!!! note
    What the default RNG is is an implementation detail.  Across different versions of
    Julia, you should not expect the default RNG to be always the same, nor that it will
    return the same stream of random numbers for a given seed.

!!! compat "Julia 1.3"
    This function was introduced in Julia 1.3.
"""
@inline default_rng() = TaskLocalRNG()
@inline default_rng(tid::Int) = TaskLocalRNG()

copy!(dst::Xoshiro, ::_GLOBAL_RNG) = copy!(dst, default_rng())
copy!(::_GLOBAL_RNG, src::Xoshiro) = copy!(default_rng(), src)
copy(::_GLOBAL_RNG) = copy(default_rng())

GLOBAL_SEED = 0
set_global_seed!(seed) = global GLOBAL_SEED = seed

function seed!(::_GLOBAL_RNG, seed=rand(RandomDevice(), UInt64, 4))
    global GLOBAL_SEED = seed
    seed!(default_rng(), seed)
end

seed!(rng::_GLOBAL_RNG, ::Nothing) = seed!(rng)  # to resolve ambiguity

seed!(seed::Union{Nothing,Integer,Vector{UInt32},Vector{UInt64}}=nothing) =
    seed!(GLOBAL_RNG, seed)

rng_native_52(::_GLOBAL_RNG) = rng_native_52(default_rng())
rand(::_GLOBAL_RNG, sp::SamplerBoolBitInteger) = rand(default_rng(), sp)
for T in (:(SamplerTrivial{UInt52Raw{UInt64}}),
          :(SamplerTrivial{UInt2x52Raw{UInt128}}),
          :(SamplerTrivial{UInt104Raw{UInt128}}),
          :(SamplerTrivial{CloseOpen01_64}),
          :(SamplerTrivial{CloseOpen12_64}),
          :(SamplerUnion(Int64, UInt64, Int128, UInt128)),
          :(SamplerUnion(Bool, Int8, UInt8, Int16, UInt16, Int32, UInt32)),
         )
    @eval rand(::_GLOBAL_RNG, x::$T) = rand(default_rng(), x)
end

rand!(::_GLOBAL_RNG, A::AbstractArray{Float64}, I::SamplerTrivial{<:FloatInterval_64}) = rand!(default_rng(), A, I)
rand!(::_GLOBAL_RNG, A::Array{Float64}, I::SamplerTrivial{<:FloatInterval_64}) = rand!(default_rng(), A, I)
for T in (Float16, Float32)
    @eval rand!(::_GLOBAL_RNG, A::Array{$T}, I::SamplerTrivial{CloseOpen12{$T}}) = rand!(default_rng(), A, I)
    @eval rand!(::_GLOBAL_RNG, A::Array{$T}, I::SamplerTrivial{CloseOpen01{$T}}) = rand!(default_rng(), A, I)
end
for T in BitInteger_types
    @eval rand!(::_GLOBAL_RNG, A::Array{$T}, I::SamplerType{$T}) = rand!(default_rng(), A, I)
end

function __init__()
    seed!(GLOBAL_RNG)
    ccall(:jl_gc_init_finalizer_rng_state, Cvoid, ())
end


### generation

# MersenneTwister produces natively Float64
rng_native_52(::MersenneTwister) = Float64

#### helper functions

# precondition: !mt_empty(r)
rand_inbounds(r::MersenneTwister, ::CloseOpen12_64) = mt_pop!(r)
rand_inbounds(r::MersenneTwister, ::CloseOpen01_64=CloseOpen01()) =
    rand_inbounds(r, CloseOpen12()) - 1.0

rand_inbounds(r::MersenneTwister, ::UInt52Raw{T}) where {T<:BitInteger} =
    reinterpret(UInt64, rand_inbounds(r, CloseOpen12())) % T

function rand(r::MersenneTwister, x::SamplerTrivial{UInt52Raw{UInt64}})
    reserve_1(r)
    rand_inbounds(r, x[])
end

function rand(r::MersenneTwister, ::SamplerTrivial{UInt2x52Raw{UInt128}})
    reserve(r, 2)
    rand_inbounds(r, UInt52Raw(UInt128)) << 64 | rand_inbounds(r, UInt52Raw(UInt128))
end

function rand(r::MersenneTwister, ::SamplerTrivial{UInt104Raw{UInt128}})
    reserve(r, 2)
    rand_inbounds(r, UInt52Raw(UInt128)) << 52 ⊻ rand_inbounds(r, UInt52Raw(UInt128))
end

#### floats

rand(r::MersenneTwister, sp::SamplerTrivial{CloseOpen12_64}) =
    (reserve_1(r); rand_inbounds(r, sp[]))

#### integers

rand(r::MersenneTwister, T::SamplerUnion(Int64, UInt64, Int128, UInt128)) =
    mt_pop!(r, T[])

rand(r::MersenneTwister, T::SamplerUnion(Bool, Int8, UInt8, Int16, UInt16, Int32, UInt32)) =
    rand(r, UInt52Raw()) % T[]

#### arrays of floats

##### AbstractArray

function rand!(r::MersenneTwister, A::AbstractArray{Float64},
               I::SamplerTrivial{<:FloatInterval_64})
    region = LinearIndices(A)
    # what follows is equivalent to this simple loop but more efficient:
    # for i=region
    #     @inbounds A[i] = rand(r, I[])
    # end
    m = Base.checked_sub(first(region), 1)
    n = last(region)
    while m < n
        s = mt_avail(r)
        if s == 0
            gen_rand(r)
            s = mt_avail(r)
        end
        m2 = min(n, m+s)
        for i=m+1:m2
            @inbounds A[i] = rand_inbounds(r, I[])
        end
        m = m2
    end
    A
end


##### Array : internal functions

# internal array-like type to circumvent the lack of flexibility with reinterpret
struct UnsafeView{T} <: DenseArray{T,1}
    ptr::Ptr{T}
    len::Int
end

Base.length(a::UnsafeView) = a.len
Base.getindex(a::UnsafeView, i::Int) = unsafe_load(a.ptr, i)
Base.setindex!(a::UnsafeView, x, i::Int) = unsafe_store!(a.ptr, x, i)
Base.pointer(a::UnsafeView) = a.ptr
Base.size(a::UnsafeView) = (a.len,)
Base.elsize(::Type{UnsafeView{T}}) where {T} = sizeof(T)

# this is essentially equivalent to rand!(r, ::AbstractArray{Float64}, I) above, but due to
# optimizations which can't be done currently when working with pointers, we have to re-order
# manually the computation flow to get the performance
# (see https://discourse.julialang.org/t/unsafe-store-sometimes-slower-than-arrays-setindex)
function _rand_max383!(r::MersenneTwister, A::UnsafeView{Float64}, I::FloatInterval_64)
    n = length(A)
    @assert n <= dsfmt_get_min_array_size()+1 # == 383
    mt_avail(r) == 0 && gen_rand(r)
    # from now on, at most one call to gen_rand(r) will be necessary
    m = min(n, mt_avail(r))
    GC.@preserve r unsafe_copyto!(A.ptr, pointer(r.vals, r.idxF+1), m)
    if m == n
        r.idxF += m
    else # m < n
        gen_rand(r)
        GC.@preserve r unsafe_copyto!(A.ptr+m*sizeof(Float64), pointer(r.vals), n-m)
        r.idxF = n-m
    end
    if I isa CloseOpen01
        for i=1:n
            A[i] -= 1.0
        end
    end
    A
end

function fill_array!(rng::MersenneTwister, A::Ptr{Float64}, n::Int, I)
    rng.adv += n
    fill_array!(rng.state, A, n, I)
end

fill_array!(s::DSFMT_state, A::Ptr{Float64}, n::Int, ::CloseOpen01_64) =
    dsfmt_fill_array_close_open!(s, A, n)

fill_array!(s::DSFMT_state, A::Ptr{Float64}, n::Int, ::CloseOpen12_64) =
    dsfmt_fill_array_close1_open2!(s, A, n)


function rand!(r::MersenneTwister, A::UnsafeView{Float64},
               I::SamplerTrivial{<:FloatInterval_64})
    # depending on the alignment of A, the data written by fill_array! may have
    # to be left-shifted by up to 15 bytes (cf. unsafe_copyto! below) for
    # reproducibility purposes;
    # so, even for well aligned arrays, fill_array! is used to generate only
    # the n-2 first values (or n-3 if n is odd), and the remaining values are
    # generated by the scalar version of rand
    n = length(A)
    n2 = (n-2) ÷ 2 * 2
    n2 < dsfmt_get_min_array_size() && return _rand_max383!(r, A, I[])

    pA = A.ptr
    align = Csize_t(pA) % 16
    if align > 0
        pA2 = pA + 16 - align
        fill_array!(r, pA2, n2, I[]) # generate the data in-place, but shifted
        unsafe_copyto!(pA, pA2, n2) # move the data to the beginning of the array
    else
        fill_array!(r, pA, n2, I[])
    end
    for i=n2+1:n
        A[i] = rand(r, I[])
    end
    A
end

# fills up A reinterpreted as an array of Float64 with n64 values
function _rand!(r::MersenneTwister, A::Array{T}, n64::Int, I::FloatInterval_64) where T
    # n64 is the length in terms of `Float64` of the target
    @assert sizeof(Float64)*n64 <= sizeof(T)*length(A) && isbitstype(T)
    GC.@preserve A rand!(r, UnsafeView{Float64}(pointer(A), n64), SamplerTrivial(I))
    A
end

##### Array: Float64, Float16, Float32

rand!(r::MersenneTwister, A::Array{Float64}, I::SamplerTrivial{<:FloatInterval_64}) =
    _rand!(r, A, length(A), I[])

mask128(u::UInt128, ::Type{Float16}) =
    (u & 0x03ff03ff03ff03ff03ff03ff03ff03ff) | 0x3c003c003c003c003c003c003c003c00

mask128(u::UInt128, ::Type{Float32}) =
    (u & 0x007fffff007fffff007fffff007fffff) | 0x3f8000003f8000003f8000003f800000

for T in (Float16, Float32)
    @eval function rand!(r::MersenneTwister, A::Array{$T}, ::SamplerTrivial{CloseOpen12{$T}})
        n = length(A)
        n128 = n * sizeof($T) ÷ 16
        _rand!(r, A, 2*n128, CloseOpen12())
        GC.@preserve A begin
            A128 = UnsafeView{UInt128}(pointer(A), n128)
            for i in 1:n128
                u = A128[i]
                u ⊻= u << 26
                # at this point, the 64 low bits of u, "k" being the k-th bit of A128[i] and "+"
                # the bit xor, are:
                # [..., 58+32,..., 53+27, 52+26, ..., 33+7, 32+6, ..., 27+1, 26, ..., 1]
                # the bits needing to be random are
                # [1:10, 17:26, 33:42, 49:58] (for Float16)
                # [1:23, 33:55] (for Float32)
                # this is obviously satisfied on the 32 low bits side, and on the high side,
                # the entropy comes from bits 33:52 of A128[i] and then from bits 27:32
                # (which are discarded on the low side)
                # this is similar for the 64 high bits of u
                A128[i] = mask128(u, $T)
            end
        end
        for i in 16*n128÷sizeof($T)+1:n
            @inbounds A[i] = rand(r, $T) + one($T)
        end
        A
    end

    @eval function rand!(r::MersenneTwister, A::Array{$T}, ::SamplerTrivial{CloseOpen01{$T}})
        rand!(r, A, CloseOpen12($T))
        I32 = one(Float32)
        for i in eachindex(A)
            @inbounds A[i] = Float32(A[i])-I32 # faster than "A[i] -= one(T)" for T==Float16
        end
        A
    end
end

#### arrays of integers

function rand!(r::MersenneTwister, A::UnsafeView{UInt128}, ::SamplerType{UInt128})
    n::Int=length(A)
    i = n
    while true
        rand!(r, UnsafeView{Float64}(A.ptr, 2i), CloseOpen12())
        n < 5 && break
        i = 0
        while n-i >= 5
            u = A[i+=1]
            A[n]    ⊻= u << 48
            A[n-=1] ⊻= u << 36
            A[n-=1] ⊻= u << 24
            A[n-=1] ⊻= u << 12
            n-=1
        end
    end
    if n > 0
        u = rand(r, UInt2x52Raw())
        for i = 1:n
            A[i] ⊻= u << (12*i)
        end
    end
    A
end

for T in BitInteger_types
    @eval function rand!(r::MersenneTwister, A::Array{$T}, sp::SamplerType{$T})
        GC.@preserve A rand!(r, UnsafeView(pointer(A), length(A)), sp)
        A
    end

    T == UInt128 && continue

    @eval function rand!(r::MersenneTwister, A::UnsafeView{$T}, ::SamplerType{$T})
        n = length(A)
        n128 = n * sizeof($T) ÷ 16
        rand!(r, UnsafeView{UInt128}(pointer(A), n128))
        for i = 16*n128÷sizeof($T)+1:n
            @inbounds A[i] = rand(r, $T)
        end
        A
    end
end


#### arrays of Bool

# similar to Array{UInt8}, but we need to mask the result so that only the LSB
# in each byte can be non-zero

function rand!(r::MersenneTwister, A1::Array{Bool}, sp::SamplerType{Bool})
    n1 = length(A1)
    n128 = n1 ÷ 16

    if n128 == 0
        bits = rand(r, UInt52Raw())
    else
        GC.@preserve A1 begin
            A = UnsafeView{UInt128}(pointer(A1), n128)
            rand!(r, UnsafeView{Float64}(A.ptr, 2*n128), CloseOpen12())
            # without masking, non-zero bits could be observed in other
            # positions than the LSB of each byte
            mask = 0x01010101010101010101010101010101
            # we need up to 15 bits of entropy in `bits` for the final loop,
            # which we will extract from x = A[1] % UInt64;
            # let y = x % UInt32; y contains 32 bits of entropy, but 4
            # of them will be used for A[1] itself (the first of
            # each byte). To compensate, we xor with (y >> 17),
            # which gets the entropy from the second bit of each byte
            # of the upper-half of y, and sets it in the first bit
            # of each byte of the lower half; the first two bytes
            # now contain 16 usable random bits
            x = A[1] % UInt64
            bits = x ⊻ x >> 17
            for i = 1:n128
                # << 5 to randomize the first bit of the 8th & 16th byte
                # (i.e. we move bit 52 (resp. 52 + 64), which is unused,
                # to position 57 (resp. 57 + 64))
                A[i] = (A[i] ⊻ A[i] << 5) & mask
            end
        end
    end
    for i = 16*n128+1:n1
        @inbounds A1[i] = bits % Bool
        bits >>= 1
    end
    A1
end


### randjump

# Old randjump methods are deprecated, the scalar version is in the Future module.

function _randjump(r::MersenneTwister, jumppoly::DSFMT.GF2X)
    adv = r.adv
    adv_jump = r.adv_jump
    s = MersenneTwister(copy(r.seed), DSFMT.dsfmt_jump(r.state, jumppoly))
    reset_caches!(s)
    s.adv = adv
    s.adv_jump = adv_jump
    s
end

# NON-PUBLIC
function jump(r::MersenneTwister, steps::Integer)
    iseven(steps) || throw(DomainError(steps, "steps must be even"))
    # steps >= 0 checked in calc_jump (`steps >> 1 < 0` if `steps < 0`)
    j = _randjump(r, Random.DSFMT.calc_jump(steps >> 1))
    j.adv_jump += steps
    j
end

# NON-PUBLIC
jump!(r::MersenneTwister, steps::Integer) = copy!(r, jump(r, steps))


### constructors matching show (EXPERIMENTAL)

# parameters in the tuples are:
# 1: .adv_jump (jump steps)
# 2: .adv (number of generated floats at the DSFMT_state level since seeding, besides jumps)
# 3, 4: .adv_vals, .idxF (counters to reconstruct the float cache, optional if 5-6 not shown))
# 5, 6: .adv_ints, .idxI (counters to reconstruct the integer cache, optional)

Random.MersenneTwister(seed::Union{Integer,Vector{UInt32}}, advance::NTuple{6,Integer}) =
    advance!(MersenneTwister(seed), advance...)

Random.MersenneTwister(seed::Union{Integer,Vector{UInt32}}, advance::NTuple{4,Integer}) =
    MersenneTwister(seed, (advance..., 0, 0))

Random.MersenneTwister(seed::Union{Integer,Vector{UInt32}}, advance::NTuple{2,Integer}) =
    MersenneTwister(seed, (advance..., 0, 0, 0, 0))

# advances raw state (per fill_array!) of r by n steps (Float64 values)
function _advance_n!(r::MersenneTwister, n::Int64, work::Vector{Float64})
    n == 0 && return
    n < 0 && throw(DomainError(n, "can't advance $r to the specified state"))
    ms = dsfmt_get_min_array_size() % Int64
    @assert n >= ms
    lw = ms + n % ms
    resize!(work, lw)
    GC.@preserve work fill_array!(r, pointer(work), lw, CloseOpen12())
    c::Int64 = lw
    GC.@preserve work while n > c
        fill_array!(r, pointer(work), ms, CloseOpen12())
        c += ms
    end
    @assert n == c
end

function _advance_to!(r::MersenneTwister, adv::Int64, work)
    _advance_n!(r, adv - r.adv, work)
    @assert r.adv == adv
end

function _advance_F!(r::MersenneTwister, adv_vals, idxF, work)
    _advance_to!(r, adv_vals, work)
    gen_rand(r)
    @assert r.adv_vals == adv_vals
    r.idxF = idxF
end

function _advance_I!(r::MersenneTwister, adv_ints, idxI, work)
    _advance_to!(r, adv_ints, work)
    mt_setfull!(r, Int) # sets r.adv_ints
    @assert r.adv_ints == adv_ints
    r.idxI = 16*length(r.ints) - 8*idxI
end

function advance!(r::MersenneTwister, adv_jump, adv, adv_vals, idxF, adv_ints, idxI)
    adv_jump = BigInt(adv_jump)
    adv, adv_vals, adv_ints = Int64.((adv, adv_vals, adv_ints))
    idxF, idxI = Int.((idxF, idxI))

    ms = dsfmt_get_min_array_size() % Int
    work = sizehint!(Vector{Float64}(), 2ms)

    adv_jump != 0 && jump!(r, adv_jump)
    advF = (adv_vals, idxF) != (0, 0)
    advI = (adv_ints, idxI) != (0, 0)

    if advI && advF
        @assert adv_vals != adv_ints
        if adv_vals < adv_ints
            _advance_F!(r, adv_vals, idxF, work)
            _advance_I!(r, adv_ints, idxI, work)
        else
            _advance_I!(r, adv_ints, idxI, work)
            _advance_F!(r, adv_vals, idxF, work)
        end
    elseif advF
        _advance_F!(r, adv_vals, idxF, work)
    elseif advI
        _advance_I!(r, adv_ints, idxI, work)
    else
        @assert adv == 0
    end
    _advance_to!(r, adv, work)
    r
end
