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[stdlib] [NFC] FloatingPointRandom.swift created (swiftlang#33463)
* Moved `random` methods out of FloatingPoint.swift * Added `random` methods to FloatingPointRandom.swift * Added FloatingPointRandom.swift to CMakeLists.txt * Added FloatingPointRandom.swift to GroupInfo.json * Moved filename within CMakeLists.txt
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‎stdlib/public/core/CMakeLists.txt

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@@ -211,6 +211,7 @@ set(SWIFTLIB_SOURCES
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CollectionOfOne.swift
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DiscontiguousSlice.swift
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Diffing.swift
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FloatingPointRandom.swift
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Mirror.swift
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PlaygroundDisplay.swift
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CommandLine.swift

‎stdlib/public/core/FloatingPoint.swift

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@@ -2013,205 +2013,4 @@ extension BinaryFloatingPoint where Self.RawSignificand: FixedWidthInteger {
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guard exact else { return nil }
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self = value_
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}
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/// Returns a random value within the specified range, using the given
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/// generator as a source for randomness.
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///
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/// Use this method to generate a floating-point value within a specific
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/// range when you are using a custom random number generator. This example
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/// creates three new values in the range `10.0 ..< 20.0`.
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///
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/// for _ in 1...3 {
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/// print(Double.random(in: 10.0 ..< 20.0, using: &myGenerator))
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/// }
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/// // Prints "18.1900709259179"
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/// // Prints "14.2286325689993"
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/// // Prints "13.1485686260762"
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///
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/// The `random(in:using:)` static method chooses a random value from a
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/// continuous uniform distribution in `range`, and then converts that value
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/// to the nearest representable value in this type. Depending on the size
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/// and span of `range`, some concrete values may be represented more
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/// frequently than others.
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///
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/// - Note: The algorithm used to create random values may change in a future
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/// version of Swift. If you're passing a generator that results in the
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/// same sequence of floating-point values each time you run your program,
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/// that sequence may change when your program is compiled using a
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/// different version of Swift.
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///
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/// - Parameters:
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/// - range: The range in which to create a random value.
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/// `range` must be finite and non-empty.
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/// - generator: The random number generator to use when creating the
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/// new random value.
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/// - Returns: A random value within the bounds of `range`.
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@inlinable
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public static func random<T: RandomNumberGenerator>(
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in range: Range<Self>,
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using generator: inout T
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) -> Self {
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_precondition(
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!range.isEmpty,
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"Can't get random value with an empty range"
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)
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let delta = range.upperBound - range.lowerBound
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// TODO: this still isn't quite right, because the computation of delta
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// can overflow (e.g. if .upperBound = .maximumFiniteMagnitude and
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// .lowerBound = -.upperBound); this should be re-written with an
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// algorithm that handles that case correctly, but this precondition
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// is an acceptable short-term fix.
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_precondition(
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delta.isFinite,
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"There is no uniform distribution on an infinite range"
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)
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let rand: Self.RawSignificand
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if Self.RawSignificand.bitWidth == Self.significandBitCount + 1 {
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rand = generator.next()
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} else {
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let significandCount = Self.significandBitCount + 1
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let maxSignificand: Self.RawSignificand = 1 << significandCount
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// Rather than use .next(upperBound:), which has to work with arbitrary
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// upper bounds, and therefore does extra work to avoid bias, we can take
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// a shortcut because we know that maxSignificand is a power of two.
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rand = generator.next() & (maxSignificand - 1)
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}
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let unitRandom = Self.init(rand) * (Self.ulpOfOne / 2)
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let randFloat = delta * unitRandom + range.lowerBound
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if randFloat == range.upperBound {
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return Self.random(in: range, using: &generator)
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}
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return randFloat
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}
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/// Returns a random value within the specified range.
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///
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/// Use this method to generate a floating-point value within a specific
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/// range. This example creates three new values in the range
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/// `10.0 ..< 20.0`.
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///
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/// for _ in 1...3 {
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/// print(Double.random(in: 10.0 ..< 20.0))
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/// }
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/// // Prints "18.1900709259179"
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/// // Prints "14.2286325689993"
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/// // Prints "13.1485686260762"
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///
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/// The `random()` static method chooses a random value from a continuous
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/// uniform distribution in `range`, and then converts that value to the
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/// nearest representable value in this type. Depending on the size and span
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/// of `range`, some concrete values may be represented more frequently than
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/// others.
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///
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/// This method is equivalent to calling `random(in:using:)`, passing in the
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/// system's default random generator.
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///
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/// - Parameter range: The range in which to create a random value.
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/// `range` must be finite and non-empty.
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/// - Returns: A random value within the bounds of `range`.
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@inlinable
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public static func random(in range: Range<Self>) -> Self {
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var g = SystemRandomNumberGenerator()
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return Self.random(in: range, using: &g)
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}
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/// Returns a random value within the specified range, using the given
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/// generator as a source for randomness.
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///
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/// Use this method to generate a floating-point value within a specific
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/// range when you are using a custom random number generator. This example
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/// creates three new values in the range `10.0 ... 20.0`.
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///
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/// for _ in 1...3 {
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/// print(Double.random(in: 10.0 ... 20.0, using: &myGenerator))
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/// }
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/// // Prints "18.1900709259179"
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/// // Prints "14.2286325689993"
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/// // Prints "13.1485686260762"
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///
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/// The `random(in:using:)` static method chooses a random value from a
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/// continuous uniform distribution in `range`, and then converts that value
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/// to the nearest representable value in this type. Depending on the size
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/// and span of `range`, some concrete values may be represented more
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/// frequently than others.
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///
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/// - Note: The algorithm used to create random values may change in a future
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/// version of Swift. If you're passing a generator that results in the
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/// same sequence of floating-point values each time you run your program,
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/// that sequence may change when your program is compiled using a
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/// different version of Swift.
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///
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/// - Parameters:
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/// - range: The range in which to create a random value. Must be finite.
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/// - generator: The random number generator to use when creating the
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/// new random value.
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/// - Returns: A random value within the bounds of `range`.
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@inlinable
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public static func random<T: RandomNumberGenerator>(
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in range: ClosedRange<Self>,
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using generator: inout T
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) -> Self {
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_precondition(
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!range.isEmpty,
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"Can't get random value with an empty range"
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)
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let delta = range.upperBound - range.lowerBound
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// TODO: this still isn't quite right, because the computation of delta
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// can overflow (e.g. if .upperBound = .maximumFiniteMagnitude and
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// .lowerBound = -.upperBound); this should be re-written with an
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// algorithm that handles that case correctly, but this precondition
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// is an acceptable short-term fix.
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_precondition(
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delta.isFinite,
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"There is no uniform distribution on an infinite range"
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)
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let rand: Self.RawSignificand
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if Self.RawSignificand.bitWidth == Self.significandBitCount + 1 {
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rand = generator.next()
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let tmp: UInt8 = generator.next() & 1
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if rand == Self.RawSignificand.max && tmp == 1 {
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return range.upperBound
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}
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} else {
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let significandCount = Self.significandBitCount + 1
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let maxSignificand: Self.RawSignificand = 1 << significandCount
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rand = generator.next(upperBound: maxSignificand + 1)
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if rand == maxSignificand {
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return range.upperBound
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}
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}
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let unitRandom = Self.init(rand) * (Self.ulpOfOne / 2)
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let randFloat = delta * unitRandom + range.lowerBound
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return randFloat
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}
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/// Returns a random value within the specified range.
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///
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/// Use this method to generate a floating-point value within a specific
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/// range. This example creates three new values in the range
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/// `10.0 ... 20.0`.
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///
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/// for _ in 1...3 {
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/// print(Double.random(in: 10.0 ... 20.0))
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/// }
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/// // Prints "18.1900709259179"
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/// // Prints "14.2286325689993"
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/// // Prints "13.1485686260762"
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///
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/// The `random()` static method chooses a random value from a continuous
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/// uniform distribution in `range`, and then converts that value to the
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/// nearest representable value in this type. Depending on the size and span
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/// of `range`, some concrete values may be represented more frequently than
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/// others.
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///
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/// This method is equivalent to calling `random(in:using:)`, passing in the
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/// system's default random generator.
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///
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/// - Parameter range: The range in which to create a random value. Must be finite.
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/// - Returns: A random value within the bounds of `range`.
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@inlinable
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public static func random(in range: ClosedRange<Self>) -> Self {
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var g = SystemRandomNumberGenerator()
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return Self.random(in: range, using: &g)
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}
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}

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