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rand(Float32, n) generates two values of the same number over and over when n is < 16 #57336

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KristofferC opened this issue Feb 10, 2025 · 5 comments · Fixed by #57338
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rand(Float32, n) generates two values of the same number over and over when n is < 16 #57336

KristofferC opened this issue Feb 10, 2025 · 5 comments · Fixed by #57338
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randomness Random number generation and the Random stdlib
Milestone
1.12

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@KristofferC
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KristofferC commented Feb 10, 2025 •
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julia> rand(Float32, 8)
8-element Vector{Float32}:
 0.20123601
 0.20123601
 0.20944309
 0.20944309
 0.22612727
 0.22612727
 0.67038965
 0.67038965
@KristofferC KristofferC added the randomness Random number generation and the Random stdlib label Feb 10, 2025
@KristofferC KristofferC added this to the 1.12 milestone Feb 10, 2025
@KristofferC KristofferC changed the title rand(Float32, 2, 2) always gives two identical columns rand(Float32, 2, 2) always gives two identical rows Feb 10, 2025
@AayushSabharwal

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@KristofferC KristofferC changed the title rand(Float32, 2, 2) always gives two identical rows rand(Float32, 2, 2) always gives two identical columns in 1.12 Feb 10, 2025
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@KristofferC
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Bisected to d09abe5, #56144, cc @giordano.

This should basically be a non-functional change

Famous last workds.

@KristofferC KristofferC changed the title rand(Float32, 2, 2) always gives two identical columns in 1.12 rand(Float32, n) generates two values of the same number over and over Feb 10, 2025
@KristofferC KristofferC changed the title rand(Float32, n) generates two values of the same number over and over rand(Float32, n) generates two values of the same number over and over when n is < 16 Feb 10, 2025
@giordano
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giordano commented Feb 10, 2025 •
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julia/stdlib/Random/src/XoshiroSimd.jl

Line 49 in cba19bf

l = _uint2float(ui, Float32)
this line does look fishy. The rest of the change was good though 😁

@giordano giordano mentioned this issue Feb 10, 2025
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@giordano giordano linked a pull request Feb 10, 2025 that will close this issue
fix typo in Float32 random number generation #57338
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randomness Random number generation and the Random stdlib
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1.12
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@giordano @KristofferC @AayushSabharwal