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Use Swift Numerics for elementary functions #28

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merged 1 commit into from Oct 19, 2020
Merged

Use Swift Numerics for elementary functions #28

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5 changes: 4 additions & 1 deletion Package.swift
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Expand Up @@ -20,11 +20,14 @@ let package = Package(
targets: ["Algorithms"]),
],
dependencies: [
.package(url: "https://github.com/apple/swift-numerics", from: "0.0.1"),
],
targets: [
.target(
name: "Algorithms",
dependencies: []),
dependencies: [
.product(name: "RealModule", package: "swift-numerics"),
]),
.testTarget(
name: "SwiftAlgorithmsTests",
dependencies: ["Algorithms"]),
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26 changes: 8 additions & 18 deletions Sources/Algorithms/RandomSample.swift
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Expand Up @@ -9,17 +9,9 @@
//
//===----------------------------------------------------------------------===//

// For log(_:) and exp(_:)
#if canImport(Glibc)
// For log(_:) and root(_:_:)
@_implementationOnly
import Glibc
#elseif canImport(ucrt)
@_implementationOnly
import ucrt
#elseif canImport(Darwin)
@_implementationOnly
import Darwin
#endif
import RealModule

//===----------------------------------------------------------------------===//
// randomStableSample(count:)
Expand Down Expand Up @@ -90,15 +82,15 @@ extension Collection {
// https://dl.acm.org/doi/pdf/10.1145/198429.198435

fileprivate func nextW<G: RandomNumberGenerator>(
k: Double, using rng: inout G
k: Int, using rng: inout G
) -> Double {
exp(log(Double.random(in: 0..<1, using: &rng)) / k)
Double.root(.random(in: 0..<1, using: &rng), k)
}

fileprivate func nextOffset<G: RandomNumberGenerator>(
w: Double, using rng: inout G
) -> Int {
Int(log(Double.random(in: 0..<1, using: &rng)) / log(1 - w))
Int(Double.log(.random(in: 0..<1, using: &rng)) / .log(1 - w))
}

extension Collection {
Expand Down Expand Up @@ -129,11 +121,10 @@ extension Collection {
result.append(self[i])
formIndex(after: &i)
}

let dk = Double(k)

while i < endIndex {
// Calculate the next value of w.
w *= nextW(k: dk, using: &rng)
w *= nextW(k: k, using: &rng)

// Find index of the next element to swap into the reservoir.
let offset = nextOffset(w: w, using: &rng)
Expand Down Expand Up @@ -198,10 +189,9 @@ extension Sequence {
result.append(el)
}

let dk = Double(k)
while true {
// Calculate the next value of w.
w *= nextW(k: dk, using: &rng)
w *= nextW(k: k, using: &rng)

// Find the offset of the next element to swap into the reservoir.
var offset = nextOffset(w: w, using: &rng) + 1
Expand Down