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MersenneTwister: clean up constructors #60185

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6429a0d
MersenneTwister: clean up constructors
rfourquet Nov 20, 2025
2629b76
use `_MersenneTwister(undef)` instead of `MersenneTwister(undef)`
rfourquet Nov 22, 2025
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42 changes: 14 additions & 28 deletions stdlib/Random/src/MersenneTwister.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -9,9 +9,9 @@ const MT_CACHE_I = 501 << 4 # number of bytes in the UInt128 cache

mutable struct MersenneTwister <: AbstractRNG
seed::Any
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@oscardssmith oscardssmith Nov 20, 2025

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does a MersenneTwister really need to store it's seed?

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@JeffBezanson JeffBezanson Nov 20, 2025

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Yes looks like this can be deleted.

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@rfourquet rfourquet Nov 20, 2025

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It's there to recreate the state of an instance from few values, so that what show outputs corresponds to a real constructor. E.g

julia> MersenneTwister("a seed")
MersenneTwister("a seed")

But I was thinking to perhaps normalize seeds into an UInt128 value and store that instead of the original seed. The example above would then look like

julia> MersenneTwister("a seed")
MersenneTwister(0xb4802685c420b29be64de36a1f90815f)

julia> MersenneTwister(0xb4802685c420b29be64de36a1f90815f)
MersenneTwister(0xb4802685c420b29be64de36a1f90815f)

This would involve an additional round with SeedHasher, but I'm precisely preparing another PR to make that much faster.

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@oscardssmith oscardssmith Nov 20, 2025

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what about just having a HashedSeed type?

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@rfourquet rfourquet Nov 22, 2025

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The user seed is removed in #60204, without an additional round with SeedHasher, by just storing two UInt128 values instead of one. Printing is uglier, but who cares.

state::DSFMT_state
vals::Vector{Float64}
ints::Vector{UInt128}
const state::DSFMT_state
const vals::Memory{Float64}
const ints::Vector{UInt128} # it's temporarily resized internally
idxF::Int
idxI::Int

Expand All @@ -21,25 +21,13 @@ mutable struct MersenneTwister <: AbstractRNG
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
global _MersenneTwister(::UndefInitializer) =
new(nothing, DSFMT_state(),
Memory{Float64}(undef, MT_CACHE_F),
Vector{UInt128}(undef, MT_CACHE_I >> 4),
MT_CACHE_F, 0, 0, Base.GMP.ZERO, -1, -1)
end

MersenneTwister(seed, 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()
Expand Down Expand Up @@ -72,8 +60,7 @@ julia> x1 == x2
true
```
"""
MersenneTwister(seed=nothing) =
seed!(MersenneTwister(Vector{UInt32}(), DSFMT_state()), seed)
MersenneTwister(seed=nothing) = seed!(_MersenneTwister(undef), seed)


function copy!(dst::MersenneTwister, src::MersenneTwister)
Expand All @@ -90,10 +77,7 @@ function copy!(dst::MersenneTwister, src::MersenneTwister)
dst
end

copy(src::MersenneTwister) =
MersenneTwister(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)

copy(src::MersenneTwister) = copy!(_MersenneTwister(undef), src)

==(r1::MersenneTwister, r2::MersenneTwister) =
r1.seed == r2.seed && r1.state == r2.state &&
Expand Down Expand Up @@ -250,7 +234,7 @@ function initstate!(r::MersenneTwister, data::StridedVector, seed)
dsfmt_init_by_array(r.state, reinterpret(UInt32, data))
reset_caches!(r)
r.adv = 0
r.adv_jump = 0
r.adv_jump = Base.GMP.ZERO
return r
end

Expand Down Expand Up @@ -561,7 +545,9 @@ end
function _randjump(r::MersenneTwister, jumppoly::DSFMT.GF2X)
adv = r.adv
adv_jump = r.adv_jump
s = MersenneTwister(r.seed, DSFMT.dsfmt_jump(r.state, jumppoly))
s = _MersenneTwister(undef)
s.seed = r.seed
copy!(s.state, DSFMT.dsfmt_jump(r.state, jumppoly))
reset_caches!(s)
s.adv = adv
s.adv_jump = adv_jump
Expand Down
12 changes: 0 additions & 12 deletions stdlib/Random/test/runtests.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -646,18 +646,6 @@ end
# MersenneTwister initialization with invalid values
@test_throws DomainError DSFMT.DSFMT_state(zeros(Int32, rand(0:DSFMT.JN32-1)))

@test_throws DomainError MersenneTwister(zeros(UInt32, 1), DSFMT.DSFMT_state(),
zeros(Float64, 10), zeros(UInt128, MT_CACHE_I>>4), 0, 0, 0, 0, -1, -1)

@test_throws DomainError MersenneTwister(zeros(UInt32, 1), DSFMT.DSFMT_state(),
zeros(Float64, MT_CACHE_F), zeros(UInt128, MT_CACHE_I>>4), -1, 0, 0, 0, -1, -1)

@test_throws DomainError MersenneTwister(zeros(UInt32, 1), DSFMT.DSFMT_state(),
zeros(Float64, MT_CACHE_F), zeros(UInt128, MT_CACHE_I>>3), 0, 0, 0, 0, -1, -1)

@test_throws DomainError MersenneTwister(zeros(UInt32, 1), DSFMT.DSFMT_state(),
zeros(Float64, MT_CACHE_F), zeros(UInt128, MT_CACHE_I>>4), 0, -1, 0, 0, -1, -1)

# seed is private to MersenneTwister
let seed = rand(UInt32, 10)
r = MersenneTwister(seed)
Expand Down