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fix #17467 1st call to rand is now non-skewed; allow seed == 0 (#17468)

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* fix #17467 1st call to rand is now non-skewed; allow passing 0 as seed

* changelog + fallback

* document behavior for seed == 0

* address comments

* _

* fix tests, disable kdtree

* re-enable kdtree with -d:nimLegacyRandomInitRand
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Timothee Cour 2021-05-11 02:04:59 -07:00 • committed by GitHub
commit 45490497e3
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4 changed files with 75 additions and 67 deletions
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31
tests/stdlib/trandom.nim
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@ -1,5 +1,5 @@
discard """
joinable: false
joinable: false # to avoid messing with global rand state
targets: "c js"
"""
@ -37,11 +37,14 @@ main()
block:
when not defined(js):
doAssert almostEqual(rand(12.5), 4.012897747078944)
doAssert almostEqual(rand(2233.3322), 879.702755321298)
doAssert almostEqual(rand(12.5), 7.355175342026979)
doAssert almostEqual(rand(2233.3322), 499.342386778917)
type DiceRoll = range[0..6]
doAssert rand(DiceRoll).int == 4
when not defined(js):
doAssert rand(DiceRoll).int == 3
else:
doAssert rand(DiceRoll).int == 6
var rs: RunningStat
for j in 1..5:
@ -164,3 +167,23 @@ block: # random sample
let stdDev = sqrt(n * p * (1.0 - p))
# NOTE: like unnormalized int CDF test, P(wholeTestFails) =~ 0.01.
doAssert abs(float(histo[values[i]]) - expected) <= 3.0 * stdDev
block:
# 0 is a valid seed
var r = initRand(0)
doAssert r.rand(1.0) != r.rand(1.0)
r = initRand(10)
doAssert r.rand(1.0) != r.rand(1.0)
# changing the seed changes the sequence
var r1 = initRand(123)
var r2 = initRand(124)
doAssert r1.rand(1.0) != r2.rand(1.0)
block: # bug #17467
let n = 1000
for i in -n .. n:
var r = initRand(i)
let x = r.rand(1.0)
doAssert x > 1e-4, $(x, i)
# This used to fail for each i in 0..<26844, i.e. the 1st produced value
# was predictable and < 1e-4, skewing distributions.