lilithhafner/aliastables.jl

An efficient sampler for discrete random variables

aliastables.jl's Issues

Downstream errors on 32bit

Downstream tests in Turing on 32bit recently started to fail due to AliasTables (or its integration in Distributions): https://github.com/TuringLang/Turing.jl/actions/runs/8868873134/job/24348938461#step:6:588

  ArgumentError: Lookup table longer than length(probablity_alias)
  Stacktrace:
    [1] _lookup_alias_table!(probability_alias::Vector{Tuple{UInt64, Int32}}, weights::AliasTables.MallocArrays.MallocArray{UInt64, 1}, mtz::Int32)
      @ AliasTables ~/.julia/packages/AliasTables/wd9Qk/src/AliasTables.jl:182
    [2] _alias_table!(probability_alias::Vector{Tuple{UInt64, Int32}}, weights::AliasTables.MallocArrays.MallocArray{UInt64, 1})
      @ AliasTables ~/.julia/packages/AliasTables/wd9Qk/src/AliasTables.jl:248
    [3] set_weights!(at::AliasTables.AliasTable{UInt64, Int32}, weights::Vector{Float64}; _normalize::Bool)
      @ AliasTables ~/.julia/packages/AliasTables/wd9Qk/src/AliasTables.jl:159
    [4] _
      @ ~/.julia/packages/AliasTables/wd9Qk/src/AliasTables.jl:115 [inlined]
    [5] #AliasTable#3
      @ ~/.julia/packages/AliasTables/wd9Qk/src/AliasTables.jl:119 [inlined]
    [6] AliasTable
      @ ~/.julia/packages/AliasTables/wd9Qk/src/AliasTables.jl:119 [inlined]
    [7] AliasTable
      @ ~/.julia/packages/Distributions/fgrZq/src/samplers/aliastable.jl:3 [inlined]
    [8] sampler
      @ ~/.julia/packages/Distributions/fgrZq/src/univariate/discrete/categorical.jl:118 [inlined]
    [9] rand(rng::StableRNGs.LehmerRNG, s::Categorical{Float64, Vector{Float64}}, dims::Tuple{Int32})
      @ Distributions ~/.julia/packages/Distributions/fgrZq/src/genericrand.jl:35
   [10] rand(::StableRNGs.LehmerRNG, ::Categorical{Float64, Vector{Float64}}, ::Int32)
      @ Distributions ~/.julia/packages/Distributions/fgrZq/src/genericrand.jl:24
...

My initial guess is that some part of AliasTables implicitly assumes that Int = Int64.

Bad & inconsistent error message when length of weights is greater than typemax(T)

julia> AliasTable{UInt8}(vcat(fill(0x00, 2^8), 0x80, 0x80))
ERROR: ArgumentError: sum(weights) is too high
Stacktrace:
 [1] _alias_table(::Type{UInt8}, ::Type{Int64}, weights0::Vector{UInt8})
   @ AliasTables ~/.julia/dev/AliasTables/src/AliasTables.jl:231
 [2] AliasTable{UInt8, Int64}(weights::Vector{UInt8}; _normalize::Bool)
   @ AliasTables ~/.julia/dev/AliasTables/src/AliasTables.jl:85
 [3] AliasTable
   @ ~/.julia/dev/AliasTables/src/AliasTables.jl:78 [inlined]
 [4] (AliasTable{UInt8})(weights::Vector{UInt8})
   @ AliasTables ~/.julia/dev/AliasTables/src/AliasTables.jl:77
 [5] top-level scope
   @ REPL[16]:1

julia> AliasTable{UInt8}(vcat(0x80, 0x80, fill(0x00, 2^8)))
AliasTable{UInt8}([0x80, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  …  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00])

AliasTables 1.0.0 (cb7b2d6)
Juila Version 1.11.0-beta1 (though this error should manifest on all Julia versions)

This is because points_per_cell rounds down to zero. We can special case long (necessarily sparse) weights by setting all accept probabilities to one pip (100%) and then we have what is effectively a lookup table sample(x::T) = table[x]::I, but with a but of overhead because the types don't tell us that we're in this case.

It's somewhat unreasonable to expect an alias table to preform adequately in this extreme case, but we can without extra costs (aside from some additional complexity isolated in a separate runtime branch), so we should.

AliasTable(UInt32[0x60000000, 0x40000000, 0x60000000]) fails on 32-bit

Broken on v1.0.0, v1.1.0, and main. Found while working on #52.

julia> AliasTable(UInt32[0x60000000, 0x40000000, 0x60000000])
ERROR: DivideError: integer division error
Stacktrace:
  [1] divrem(x::UInt128, y::UInt128)
    @ Base ./int.jl:828
  [2] div
    @ ./int.jl:867 [inlined]
  [3] div
    @ ./div.jl:252 [inlined]
  [4] div
    @ ./div.jl:37 [inlined]
  [5] normalize_to_uint!(res::AliasTables.MallocArrays.MallocArray{UInt64, 1}, v::Vector{UInt32}, sm::UInt32)
    @ AliasTables ~/.julia/dev/AliasTables/src/AliasTables.jl:631
  [6] set_weights!(at::AliasTable{UInt64, Int32}, weights::Vector{UInt32}; _normalize::Bool)
    @ AliasTables ~/.julia/dev/AliasTables/src/AliasTables.jl:158
  [7] _
    @ ~/.julia/dev/AliasTables/src/AliasTables.jl:115 [inlined]
  [8] #AliasTable#1
    @ ~/.julia/dev/AliasTables/src/AliasTables.jl:76 [inlined]
  [9] AliasTable(weights::Vector{UInt32})
    @ AliasTables ~/.julia/dev/AliasTables/src/AliasTables.jl:119
 [10] top-level scope
    @ REPL[21]:1

`AliasTable{UInt8}(fill(1.0, 1000))` throws

julia> AliasTable{UInt8}(fill(1, 1000))
AliasTable{UInt8}([0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01  …  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00])

julia> AliasTable{UInt8}(fill(1.0, 1000))
ERROR: ArgumentError: all weights are zero
Stacktrace:
 [1] get_only_nonzero
   @ ~/.julia/packages/AliasTables/yt2Qj/src/AliasTables.jl:124 [inlined]
 [2] normalize_to_uint(::Type{UInt8}, v::Vector{Float64}, sm::Float64)
   @ AliasTables ~/.julia/packages/AliasTables/yt2Qj/src/AliasTables.jl:465
 [3] AliasTable{UInt8, Int64}(weights::Vector{Float64}; _normalize::Bool)
   @ AliasTables ~/.julia/packages/AliasTables/yt2Qj/src/AliasTables.jl:87
 [4] AliasTable
   @ ~/.julia/packages/AliasTables/yt2Qj/src/AliasTables.jl:78 [inlined]
 [5] (AliasTable{UInt8})(weights::Vector{Float64})
   @ AliasTables ~/.julia/packages/AliasTables/yt2Qj/src/AliasTables.jl:77
 [6] top-level scope
   @ REPL[5]:1

Need CI tests for 32 bits.

See also #48

Need CI tests for 32 bits.

See also #48

`AliasTable([0x0ffffffffffffffff000000000000000, 0x0ffffffffffffffff000000000000000])` throws

julia> AliasTable{UInt8}([0x0ffffffffffffffff000000000000000, 0x0ffffffffffffffff000000000000000])
ERROR: BoundsError: attempt to access 2-element Vector{UInt8} at index [242]
Stacktrace:
 [1] throw_boundserror(A::Vector{UInt8}, I::Tuple{Int64})
   @ Base ./essentials.jl:14
 [2] getindex
   @ ./essentials.jl:891 [inlined]
 [3] normalize_to_uint(::Type{UInt8}, v::Vector{UInt128}, sm::UInt128)
   @ AliasTables ~/.julia/packages/AliasTables/yt2Qj/src/AliasTables.jl:488
 [4] AliasTable{UInt8, Int64}(weights::Vector{UInt128}; _normalize::Bool)
   @ AliasTables ~/.julia/packages/AliasTables/yt2Qj/src/AliasTables.jl:87
 [5] AliasTable
   @ ~/.julia/packages/AliasTables/yt2Qj/src/AliasTables.jl:78 [inlined]
 [6] (AliasTable{UInt8})(weights::Vector{UInt128})
   @ AliasTables ~/.julia/packages/AliasTables/yt2Qj/src/AliasTables.jl:77
 [7] top-level scope
   @ REPL[6]:1

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`rand(ot, n)::Vector{Any}`

Unsigned output type fails

julia> AliasTable{UInt, UInt}([1,2,3])
ERROR: InexactError: convert(UInt64, -2)
Stacktrace:
  [1] throw_inexacterror(::Symbol, ::Vararg{Any})
    @ Core ./boot.jl:748
  [2] check_sign_bit
    @ ./boot.jl:754 [inlined]
  [3] toUInt64
    @ ./boot.jl:865 [inlined]
  [4] UInt64
    @ ./boot.jl:895 [inlined]
  [5] convert
    @ ./number.jl:7 [inlined]
  [6] cvt1
    @ ./essentials.jl:587 [inlined]
  [7] ntuple
    @ ./ntuple.jl:49 [inlined]
  [8] convert
    @ ./essentials.jl:589 [inlined]
  [9] setindex!
    @ ./genericmemory.jl:211 [inlined]
 [10] _alias_table!(probability_alias::Memory{Tuple{UInt64, UInt64}}, weights::AliasTables.MallocArrays.MallocArray{UInt64, 1})
    @ AliasTables ~/.julia/dev/AliasTables/src/AliasTables.jl:312
 [11] set_weights!(at::AliasTable{UInt64, UInt64}, weights::Vector{Int64}; _normalize::Bool)
    @ AliasTables ~/.julia/dev/AliasTables/src/AliasTables.jl:159
 [12] set_weights!
    @ ~/.julia/dev/AliasTables/src/AliasTables.jl:145 [inlined]
 [13] _
    @ ~/.julia/dev/AliasTables/src/AliasTables.jl:115 [inlined]
 [14] AliasTable{UInt64, UInt64}(weights::Vector{Int64})
    @ AliasTables ~/.julia/dev/AliasTables/src/AliasTables.jl:110
 [15] top-level scope
    @ REPL[18]:1