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[SR-8178] BinaryFloatingPoint.random(in range: Range<Self>) can return range.upperBound #50710

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t-ae opened this issue Jul 5, 2018 · 7 comments
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[SR-8178] BinaryFloatingPoint.random(in range: Range<Self>) can return range.upperBound #50710

t-ae opened this issue Jul 5, 2018 · 7 comments
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@Azoy
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. standard library Area: Standard library umbrella

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@t-ae
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t-ae commented Jul 5, 2018

Previous ID SR-8178
Radar rdar://problem/41851227
Original Reporter @t-ae
Type Bug
Status Resolved
Resolution Done
Environment

Xcode 10 beta 3

Additional Detail from JIRA
Votes 0
Component/s Standard Library
Labels Bug
Assignee @Azoy
Priority Medium

md5: 83a421c73c3382bd6a76eed3617b3d1c

Issue Description:

BinaryFloatingPoint.random(in range: Range<Self>) can return range.upperBound (obviously out of range) for specific range.

test code:

struct AlwaysMaxRNG: RandomNumberGenerator {
    mutating func next() -> UInt64 {
        return UInt64.max
    }
}

var rng = AlwaysMaxRNG()

print("Float:")
let floatRanges: [Range<Float>] = [0..<1, 1..<2, 2..<4]
for range in floatRanges {
    print("\(range): maximum < upperBound: \(.random(in: range, using: &rng) < range.upperBound)")
}

print("\nDouble:")
let doubleRanges: [Range<Double>] = [0..<1, 1..<2, 2..<4]
for range in doubleRanges {
    print("\(range): maximum < upperBound: \(.random(in: range, using: &rng) < range.upperBound)")
}

output:

Float:
0.0..<1.0: maximum < upperBound: true
1.0..<2.0: maximum < upperBound: false
2.0..<4.0: maximum < upperBound: false

Double:
0.0..<1.0: maximum < upperBound: true
1.0..<2.0: maximum < upperBound: false
2.0..<4.0: maximum < upperBound: false
@belkadan
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belkadan commented Jul 5, 2018

cc @stephentyrone, @moiseev

@stephentyrone
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Yup, there are a bunch of related issues with this requiring some rework that I'm going to take a look at. This is as good a bug as any for the purpose.

@stephentyrone
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@swift-ci create.

@stephentyrone
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[note that this "RNG" is a great test case to add to the test suite while we're at it.]

@Azoy
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Azoy commented Jul 5, 2018

Oh sorry @stephentyrone, I thought this could have two assignees! I'll try and take a look at this one.

@stephentyrone
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No worries; if you get to it before me just tag me as a reviewer.

@Azoy
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Azoy commented Jul 6, 2018

This is resolved in: apple/swift#17794

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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@Azoy Azoy

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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. standard library Area: Standard library umbrella
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@stephentyrone @belkadan @Azoy @t-ae